R&D for the Energy Transition

Annual Report 2023 / 24

The cover illustration shows a detail of an InCellPlate® electro-plating facility to metallize siliconwafers. In this process, local metal contacts of electrically conductive copper are deposited onto
the raw wafers in an electrolyte bath.
The use of electro-plated copper instead of the commercially widespread, printed silver contacts
on silicon solar cells was developed at Fraunhofer ISE and will now be industrialized by PV2+, a
new spin-off company originating from the Institute. The technology offers essential benefits –for instance, cost advantages can be expected for solar cells with copper contacts. In addition,copper is readily available in Germany and easily recycled. This allows solar cell production to
become more sustainable.

Results and Figures

Annual Report 2023 / 24

Foreword

Recent years have revealed the vulnerability of the European
energy supply. Alongside the goal of climate neutrality, thedemand for increased resilience will thus be stronger in future.
More than 40 years ago, Fraunhofer ISE had already begun toaddress the increasingly urgent questions relating to a sustain­
able energy supply. One person, who recognized many of thesequestions well in advance and who laid the basis for successful
work at the Institute with his own contributions, passed awaylast year – Prof. Adolf Goetzberger, the founding Director of
Fraunhofer ISE, died on 24th February, 2023 at the age of 94.
We remember the visionary work of Adolf Goetzberger withgreat respect and gratitude und humbly honor his lifelong
scientific achievements and untiring efforts for research on
solar energy systems.
His activity is simultaneously an example and a stimulus todevelop the research fields at the Institute further, continuallyand consistently, so that important contributions toward
successful implementation of the energy transition can also
be delivered in future. So that we can react better to thegrowing demand for systemic solutions, we have redesigned
the internal structure of Fraunhofer ISE and grouped relevant
competences more closely together. Since July 2023, theInsti­tute is organized in four Divisions, Photovoltaics, Power
Solutions, Heat and Buildings, and Hydrogen Technologies.
In addition, we have established the program line “Overarching
System Integration” to react to the increasing demand forcomprehensive, complete solutions for resilient and ultimately
climate-neutral energy supply to industrial real estate andneighborhoods.

Foreword

At the end of September, we were very pleased to have theopportunity to greet the new President of the FraunhoferGesellschaft, Prof. Holger Hanselka, in Freiburg. Prof. Hanselka
assumed office with the goal of advancing the mission of the
Fraunhofer-Gesellschaft to reinforce the economy and further
strengthen its position as an essential supplier of innovation tosmall, medium-sized and large enterprises. Cooperation withindustry is also our focus at Fraunhofer ISE: Our activities will
be directed toward eight new, market-oriented Business Areas
from 2024 onward.
In the field of photovoltaics, we are promoting the reestablishment of a PV industry in Europe. We are supporting
the industry here with feasibility and economic viability
analyses, but also by developing the next generation ofphotovoltaics on the basis of multi-junction solar cells. The
establishment of a European solar economy is also being
pursued with high priority in Germany, and research andindustry need rapid governmental support in this process. At
the invitation of Fraunhofer ISE, around one hundred actors in
the photovoltaic branch gathered at Fraunhofer ENIQ in Berlinin July to discuss possible cooperation for new PV production
facilities in Germany. The focus of our research work for thesolar industry continues to be the development of new cells,
components and modules, and quality assurance in applica­
tions. To test and measure PV modules, we officially opened
our outdoor test field in Merdingen near Freiburg in May,
allowing us to combine laboratory measurements with out­door analyses.
In 2023, the building sector was very much at the center ofpublic attention and heat pumps were widely discussed. We
continue to conduct intensive research on improving heatpumps, particularly concerning the application of naturalrefrigerants such as propane. In close cooperation with
manufacturers and the housing sector, we are developing
heat pump systems for existing apartment buildings andscientifically accompany demonstration projects and field tests.
The revised version of the German building energy law (GEG),
which was adopted in 2023 after vehement public discussion,
ushers in the changeover to heating with renewable energy
sources. We see this as an incentive to proceed with develop­
ing practicable solutions for a successful heating transition andto make heat pump technology more cost-effective and yet
more widely applicable.

and one of the Institute Directors, Prof. Andreas Bett. We
heartily congratulate Dr. Ralf Preu for his successful postdoctoral treatise on the topic of PERC technology for solar
cells, Prof. Sonia Dsoke on her appointment to the Chair for“Electrochemical Energy Carrier and Storage Systems” andProf. Holger Neuhaus on his appointment to the Chair for“Material Systems for Solar Energy Use”. Both professorships
are at the Department of Sustainable Systems Engineering(INATECH) in the Faculty of Engineering of the University ofFreiburg and are associated with work at Fraunhofer ISE. Simi­
larly, we congratulate Dr. Peter Schossig on his appointment to
the Chair for “Technologies for Climate-Appropriate Buildings
and Neighborhoods” at the Karlsruhe Institute of Technology(KIT). This professorship, which will start on 1st April, 2024, isalso combined with work at Fraunhofer ISE.
The conversion of our global energy system to include large
shares of energy from renewable sources will be successful
only if all requirements on sustainability are met. We havethus incorporated the topic of sustainability as a core element
into our Institute strategy. We intend to include sustainability
questions consistently both from the beginning of our researchand development work and also by successively transforming
our Institute’s operation to become climate-neutral. An
important step in this direction was the certification forenergy management according to the DIN EN ISO 50001:2018
standard, which was achieved in September. As one of thefirst Fraunhofer Institutes to be certified according to thisstandard, we simultaneously prepared a template whichshould significantly accelerate the certification process forfurther Fraunhofer Institutes.
We extend our sincere gratitude to our Board of Trustees,industrial partners, scholarship donors, and funding agentsin the Ministries at the Federal and State levels, as well as
our project partners, for their trust in our work as well as
their support and funding of Fraunhofer ISE. We are very muchlooking forward to further cooperation.

Prof. Hans-Martin Henning		
We were particularly pleased about the prizes and awards
which members of the Institute staff received this year for
their scientific work. We would like to highlight the HerthaSponer Prize, with which the Deutsche Physikalische Gesell­schaft recognized Dr. Juliane Borchert for her work on newsolar cell materials and the Research Prize of the Werner Sie­mens Foundation (WSS) accompanied by prize money of
one million euros, which was awarded to Dr. Frank DimrothProf. Andreas Bett

Contents

Facts and Figures����������������������������������������������������������������������������������������������������� 6
Strategy and Business Areas ������������������������������������������������������������������������������� 22
Highlights of our Research ��������������������������������������������������������������������������������� 52
Events in 2024 ������������������������������������������������������������������������������������������������������� 87
Editorial Notes������������������������������������������������������������������������������������������������������ 88
Photo Credits�������������������������������������������������������������������������������������������������������� 88

Our newsletters offer
regular updates on our
research highlights.

4Facts and Figures		

6

Facts and Figures

Contents
Organizational Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
In Memoriam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Board of Trustees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
The Institute in Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Networking within the Fraunhofer-Gesellschaft . . . . . . . . . . . . . . . . . . . . . . . 14
Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Working at Fraunhofer ISE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Doctoral Theses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Professorships and Lectureship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Prizes and Awards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7Facts and Figures

Organizational StructureFraunhofer ISE is structured, apart fromadministrative and staff units, into fourlarge scientific Divisions: Photovoltaics,
Power Solutions, Heat and Buildings, andHydro­gen Technologies. In addition, theInstitute has establish­ed the program line
“Overarching System Integration”.

Institute Directors

We operate in eight market-oriented businessareas for external representation:

Administrative Director

Photovoltaics: Materials, Cells and Modules
Photovoltaics: Production Technology
and Transfer
Solar Power Plants and Integrated
Photovoltaics
Power Electronics and Grids
Electrical Energy Storage
Climate-Neutral Heat and Buildings
Hydrogen Technologies
System Integration
Fraunhofer ISE is supported by long-standing
mentors and experienced experts in the solar
energy sector:

Prof. Andreas BettPhone +49 761 4588-5257

Saskia Vormfelde
Phone +49 761 4588-5917

Heads of Photovoltaics Division
Prof. Stefan Glunz
Phone +49 761 4588-5191
Dr. Ralf Preu
Phone +49 761 4588-5260

Head of Power Solutions Division
Dr. Harry Wirth
Phone +49 761 4588-5858

Head of Heat andBuildings Division

Prof. Joachim Luther(Institute Director 1993 – 2006)

Dr. Peter Schossig
Phone +49 761 4588-5130

Prof. Volker Wittwer(Deputy Institute Director 1997 – 2009)

Heads of Hydrogen
Technologies Division (interim)Prof. Eicke R. Weber
(Institute Director 2006 – 2016)
From left to right:

Prof. Hans-Martin HenningPhone +49 761 4588-5134

Ulf GroosDr. Achim Schaadt
Dr. Tom Smolinka
Robert Szolak
Phone +49 761 4588-0

Prof. Hans-Martin Henning,
Prof. Andreas Bett,
Saskia Vormfelde,Prof. Stefan Glunz,
Dr. Ralf Preu,
Dr. Harry Wirth,
Dr. Peter Schossig,
Prof. Christof Wittwer

8Program Line:
Overarching System Integration
Prof. Christof Wittwer
Phone +49 761 4588-5115

Facts and Figures

In Memoriam

The solar pioneer and founder of the Fraunhofer Institutefor Solar Energy Systems ISE, Prof. Adolf Goetzberger, diedon 24th February 2023, at the age of 94. With his death,Fraunhofer ISE has lost a greatly valued scientist and visionary
prophet of solar energy, who supported the Institute with his
advice to the end of his life.
It was against appreciable resistance that Adolf Goetzberger,
then the Director of the Fraunhofer Institute for Applied Solid
State Physics IAF, succeeded first in creating a dedicatedworking group on solar energy systems and then in establish­
ing an independent Fraunhofer Institute Adolf Goetzberger led
Fraunhofer ISE from its foundation until he reached retirement
age in 1993. The Institute, in which the congruence of techno­
logy for solar energy and for energy systems was recognizedand put into practice, grew rapidly to become one of theleading institutes for solar research and is the largest solar
research institute in Europe today.
After studying experimental physics, Adolf Goetzberger com­pleted his doctoral dissertation at the University of Munich on
the crystallization of evaporated antimony layers in 1955. He
subsequently worked together with the Nobel Prize winnerand co-inventor of the transistor, William Shockley, in Californian Palo Alto and the famous Bell Laboratories in Murray
Hill, New Jersey. In 1968 he returned to Germany and became
the Director of the Fraunhofer Institute for Applied Solid State
Physics IAF. In 1971, he was appointed as an honorary profes­
sor to the Faculty of Physics at the University of Freiburg andsupervised many undergraduate and doctoral theses in thiscapacity.

The solar pioneer and founder of Fraunhofer ISE,
Prof. Adolf Goetzberger, died on 24th February,
2023, aged 94.

working groups. Just one example: Adolf Goetzberger was the
President of the Deutsche Gesellschaft für Sonnenenergie DGS(German Society for Solar Energy) from 1993 to 1997.

“I was often asked how I came to focus specifically on solar
energy, which was not taken seriously at all as an energy
source at that time”, wrote Adolf Goetzberger in 2018 in his
memoirs. In particular, the study published by the Club ofRome in 1972 on “The Limits to Growth” had fascinated him.
It seemed logical to him that we humans must use the sun as
an inexhaustible source of energy, as the fossil fuel reserves
were finite.

The meritorious contributions of Adolf Goetzberger to the utili­zation of solar energy were recognized in many different ways:
In 1983, Adolf Goetzberger was the first German to receive
the J. J. Ebers Award of the American IEEE Electron Devices
Society, for the development of the silicon field-effect transis­
tor. He was honored with the Order of Merit of the State of
Baden-Württemberg in 1989 and with the Order of Merit, FirstClass, of the Federal Republic of Germany in 1992. The Inter­national Solar Energy Society (ISES) presented him the Achieve­
ment through Action Award in 1993. In 1995, he received anhonorary doctorate from the University of Uppsala and theFarrington Daniels Award of ISES. These were followed in 1997
by the Karl Boer Medal, the Becquerel Prize and the William R.
Cherry Award. In 2006, the Solar World AG honored him with
the Einstein Award and EUROSOLAR bestowed him with theEuropean Solar Award. For his work throughout his lifetime,the European Patents Office recognized him with the European
Inventor Prize in 2009.

Adolf Goetzberger held more than 30 patents; the idea ofagri-photovoltaics, which he already developed together with
Dr. Armin Zastrow in 1981, is now experiencing its break­through. His participation and opinion were greatly appreciat­
ed in many evaluation committees, boards, commissions and

The Directorate and all staff members of Fraunhofer ISE pay
tribute to the lifelong achievements of Adolf Goetzberger.
They are grateful for his successful efforts to develop solar
energy systems and for his great resulting contribution toward
a global energy transition.

9

Facts and Figures

ProfileObjective

Services

The Fraunhofer Institute for Solar Energy Systems ISE is thelargest solar energy research institute in Europe. Our staff ofmore than 1400 is committed to an energy supply system
which is based on renewable energy sources and is sustain­
able, economic, secure and socially just. We contribute to thisin our research focusing on energy supply, energy distribu­
tion, energy storage and energy utilization. We support thesustainable transformation of the energy system by excellent
research results, successful industry projects, spin­off establish­
ment and global cooperation. Fraunhofer ISE is financed by a
combination of institutional funding and special programs of
the Fraunhofer­Gesellschaft and other sources (17 percent).
Around 62 percent of the total income is public funding(sources: German Federal Government, German States andEU), 21 percent originates from commissions from industry.
The total budget of the Institute amounted to 135.3 million
euros in 2023 (preliminary). Fraunhofer ISE is certified
according to the quality management standard
DIN EN ISO 9001:2015.

Fraunhofer ISE is equipped with excellent technical infrastruc­ture. A laboratory floor area of 22 300 m2 – including a clean­room area of 900 m2 – and extremely modern equipment andfacilities form the basis for our competence in research anddevelopment.

Research Approach
Our aspiration is to develop concretely implementable, tech­nical solutions which we provide to our industrial partners or
prepare jointly with them. This is in accordance with the Fraun­
hofer principle of applied research and simultaneously makes
an important contribution to securing the economic future
and competitiveness of Germany and Europe. The success ofapplied research also demands the interaction with politics andsociety, which is all part of our work.
Fraunhofer ISE addresses eight market­oriented business areas(page 30 ff.). Our research approach ranges from materials
research through component development up to systems
integration. As systemic questions have become increasingly
relevant in the context of the energy transition, Fraunhofer ISE
established a new organizational structure in July 2023 topromote yet greater interdisciplinarity and interaction within its
research (p. 26).

10

Our infrastructure of the highest technical standard encom­
passes eight R&D Centers and four production­relevantTechnology Evaluation Centers (pages 46 ff.). Furthermore,
the Institute offers testing and certification services in its test
and calibration laboratories that are accredited according
to DIN EN ISO 17025. On this basis, we operate as a reliable
partner and implement R&D projects at the different levels ofa technological lifecycle – exactly as required by the individual
contracts, demands and levels of maturity.
Our activities encompass:
New material / process
Prototype / pilot series
Patent / license
Software / application
Measurement­based analysis / quality control
Consultancy / planning / studies

Main building of Fraunhofer ISE.

Daten und Zahlen

Board of Trustees

The Board of Trustees assesses the research projects andadvises the Institute Directorate and the Executive of the
Fraunhofer­Gesellschaft with regard to the work programof Fraunhofer ISE.

Members of the Board of Trustees as well as external
participants of the Board meeting in July 2023.
From left to right: Jürgen Heizmann, Pia von Ardenne,

Chairman

Dr. Stefan Reber, Burkhard Holder, Prof. Michael Bauer,
Dr. Ingrid Vogler, Dr. Joachim Kloock, Peter Schneidewind,

Burkhard Holder
VDE Renewables GmbH, Alzenau

Dr. Norbert Schiedeck, Ullrich Bruchmann, Prof. Anke Weidlich,
Sibylle Hepting-Hug, Thomas Speidel.

Members
Prof. Michael Bauer
Drees & Sommer SE, Stuttgart

Prof. Armin Schnettler
Profas Energy Consult, Grünwald

Ullrich Bruchmann
German Federal Ministry for Economic
Affairs and Climate Action (BMWK), Berlin

Dr. Lioudmila Simon
E.ON Group Innovation, Essen

Dr. Gunter Erfurt
Meyer Burger AG
Jürgen Heizmann
JENOPTIK Optical Systems GmbH, Jena
Sibylle Hepting-Hug
Ministry of the Environment, Climate Protection andthe Energy Sector Baden­Württemberg, Stuttgart
Prof. Wolfram Münch
EnBW Energie Baden­Württemberg AG, KarlsruheThomas Speidelads­tec GmbH, Nürtingen
Prof. Frithjof StaißCenter for Solar Energy and Hydrogen
Research Baden­Württemberg (ZSW),
Stuttgart
Dr. Ingrid Vogler
GdW Bundesverband deutscher Wohnungs­
und Immobilienunternehmen e.V., Berlin

Dr. Norbert Schiedeck
Vaillant Group, RemscheidProf. Anke Weidenkaff
Fraunhofer Research Institution for Materials
Recycling and Resource Strategies IWKS,
Alzenau

Peter Schneidewind
RENA Technologies GmbH, Gütenbach

Prof. Anke Weidlich
University of Freiburg(Status: 31.12.2023)

11

Facts and Figures

Income in Million Euros

Expenditure in Million Euros

12

Patents

Facts and Figures

Personnel

Personnel in 2023

Lecture Courses and Seminars

13Facts and Figures

Networking within the
Fraunhofer­Gesellschaft
Fraunhofer ISE contributes a wide spectrum ofcompetence to various associations and alliances by
its networking within the Fraunhofer-Gesellschaft.
This approach particularly benefits work on systemic
questions.

Groups and Strategic Research Fields
The Fraunhofer Institutes work together within competence­oriented Groups. Fraunhofer ISE is a member, together withthree other Institutes, of the Fraunhofer Group for Energy Tech­
nologies and Climate Protection, which was founded in January
2021. Prof. Hans­Martin Henning is the Chairman of this Group.
In addition, Fraunhofer ISE is a guest member of the Fraunhofer
MATERIALS Group addressing Materials and Components.
The Fraunhofer-Gesellschaft defines Strategic Research Fields
so that it can react more specifically to research topics of the
future and establish unique scientific-technological emphases.
Fraunhofer ISE is represented in a leading role in two of theseven research fields: The Institute Director, Prof. Hans-Martin
Henning, and Prof. Welf­Guntram Drossel, Director of the
Fraunhofer Institute for Machine Tools and Forming Technology
IWU, are the Speakers for the Research Field of “Resource Efficiency and Climate Technologies”. Prof. Christopher Hebling,
Director of International Affairs at Fraunhofer ISE, and Prof.
Mario Ragwitz from the Fraunhofer Research Institution for
Energy Infrastructures and Geothermal Systems IEG are the
Speakers responsible for the Research Field of “Hydrogen
Technologies”.

The Fraunhofer Energy Alliancepresented itself with a joint
booth at the trade fair E-worldenergy & water in Düsseldorf
from 23rd to 25th May, 2023.

14

Fraunhofer Alliances for Lead Markets
Parallel to scientific excellence, transfer of results tothe economic sector and society at large is also a
focus of applications­oriented research. In this context,
the Fraunhofer­Gesellschaft has defined nine leadmarkets which are addressed with high priority by
the sector­oriented Fraunhofer Alliances.
Fraunhofer ISE is not only one of currently 19 members of
the Fraunhofer Energy Alliance but has also been responsi­
ble for its management since its establishment in 2003. The
Institute Director, Prof. Hans­Martin Henning, represents
the goals of the Alliance to the outside world as its Speaker.
Together with the Fraunhofer Battery and Water Systems(SysWasser) Alliances, in which Fraunhofer ISE is also an
active member, the Fraunhofer Energy Alliance organizes
joint market access for its member Institutes and responds
to the needs of the leading energy­economic markets.
As one of the largest energy research associations in
Europe, the Alliance offers R&D services in the fields ofEnergy Renewable, Energy Storage, Energy Efficient, Energy
Digital, Energy System, Energy Urban, Energy Grids, andEnergy | Climate | Environment. Further networking within
the Fraunhofer­Gesellschaft includes memberships in the
Building Innovation and Aviation & Space Alliances, as wellas in the Fraunhofer Cluster of Excellence on Integrated
Energy Systems (CINES) and the Fraunhofer Networks for
Sustainability and Hydrogen.

Facts and Figures

Cooperation

Scientific excellence depends on discourse between
experts. Fraunhofer ISE is integrated into an excellent
network at both the national and the international
levels.

Cooperation with Universities
Fraunhofer ISE places great value on educating future scien­tists. Currently, 46 employees teach at universities; about
230 B.Sc., M.Sc. and Ph.D students work at the Institute. In
addition, Fraunhofer ISE cooperates directly with numerous
universities in Germany and around the world.
Cooperation with the University of Freiburg is particularly
intensive. There is close collaboration with the Departmentof Sustainable Systems Engineering – INATECH within the
Faculty of Engineering, which focuses on sustainable mate­rials, energy systems and resilience. INATECH is based on aclose partnership between the University of Freiburg and thefive Fraunhofer Institutes located in Freiburg. This basis makes
INATECH unique in the research landscape and allows it tocover the complete spectrum from fundamental researchthrough to industrial application. This cooperation is comple­
mented by the Sustainability Center Freiburg, which promotes
networking with enterprises, associations and other actors
from Freiburg and the surrounding region on the topic ofsustainability.

Fraunhofer ISE also participates actively in many other central
institutions and activities of the University of Freiburg. For
example, we are contributing our expertise on photovoltaics
to the livMatS Cluster of Excellence. For more than two
decades, there has been close cooperation with the Freiburg
Materials Research Center (FMF), where our activities on orga­
nic photovoltaics and battery research are located, for exam­ple. Similarly, we have a tradition of close cooperation with theFaculties of Physics, the Environment and Natural Resources,
and Chemistry.
Among the courses which Fraunhofer ISE has initiated incooperation with the University of Freiburg are the B.Sc. and
M.Sc. courses on “Sustainable Systems Engineering” andthe M.Sc. courses on “Renewable Energy Engineering andManagement” and “Solar Energy Engineering”.

Memoranda of Understanding
In addition, the Institute signed 16 Memoranda of Understand­ing with enterprises, organizations and research institutes
around the world in 2023. The Institute is well connected at
the national and the international levels within research andprofessional associations.

Students in Freiburg:
Fraunhofer ISE has committed
itself to educate future scientists
by diverse forms of cooperation.

15

Facts and Figures

Working at Fraunhofer ISE

Since its foundation, Fraunhofer ISE has grown continuallyand is now one of the largest Institutes within the Fraunhofer­
Gesellschaft. The relevance of our stated goal – a sustainable
and socially just energy supply without fossil fuels – has also
increased enormously in the public arena. This success isinconceivable without our excellent laboratory infrastructure
but depends even more on the know­how, the commitment
and creativity of our staff of more than 1400 – because scienceand its transfer into politics, industry and society depend on
the people who are responsible for implementation. Selecting
staff members for the Institute and encouraging them to staythere thus have high priority for us. It is with good reason
that the Fraunhofer­Gesellschaft is among the most popular
employers in Germany.

Multi-Facetted Tasks with a Perspective

Shaping the Energy Transition Together

A good work­life balance is increasingly important in themodern working world. We thus offer our staff members:“Working at Fraunhofer ISE means more than just having
a job”, underlines Thomas Arnsberg, who heads Human
Resources at the Institute. “It means doing something mean­
ingful for the future every day. That applies equally well to thescientific employees as to those in administration. We are allacting in concert.” The intention to work together toward a
common goal is tangible: the positive and constructive wayof cooperating at the Institute is endearingly called the “ISEspirit” by many insiders. Beyond this, the working culture andco­existence at Fraunhofer ISE is guided by values such as
tolerance and equal opportunity – regardless of origin,religion, gender or age.

We open doors toknowledge growth.
Change starts with us.

16

Our staff members work on all facets of the energy transition.
In our research Divisions for Photovoltaics, Power Solutions,
Heat and Buildings, and Hydrogen Technologies, we offer
attractive perspectives for young employees and doctoral can­didates as well as for experts and managers with professional
experience. At Fraunhofer ISE, we welcome not only scientists
but also technicians, engineers and administrative experts.
We also offer apprenticeships in IT, technical and commercial
fields.

From Personal Development Programs toan Outdoor Terrace

Collegial and constructive cooperation
Individual and flexible working hours withthe option of home office
Very modern workspace and laboratory
infrastructure
Rebates for childcare, holiday activities forschoolchildren, pme family service
Hansefit, subsidy for a public transport ticket,
retirement provision (VBL)
Specific talent development via diverse personal
development programs for different target groups
Varied and healthy lunch from our canteen witha large outdoor terrace

Facts and Figures

Strengthening the Position of Women in Science
It is our stated goal to strengthen the position of women inscience. At present, about 22 percent of the scientific staff
at Fraunhofer ISE consists of women. We aim to increase thisshare to 25 percent in 2025 and 30 percent in 2030. In addi­tion, we are aiming to have 25 percent of managerial positions
occupied by women in 2025 and 30 percent in 2030.
Among other initiatives, our professional development
programs are contributing to this process. They are directed
toward different target groups at different career levels. We
already start with the undergraduate employees with the “ISE
Young Talents” Program, which allows 40 students each year
to discover the diverse research areas of Fraunhofer ISE withlaboratory tours, networking events and expert lectures. The
students are able to experience work beyond the sphere of
their own working group and link up with other employees
at the Institute. Beyond that, we accompany them in training
courses and workshops in professional and personal develop­
ment. At least 50 percent of the available places are allocatedto women.

Further Professional Development Programs
DokInCareer for female doctoral candidates
Femovation for female scientists with their own
project ideas
TALENTA start, TALENTA speed up and TALENTA excellence
for female scientists at three different stages of their careers
With the help of these programs, we make it feasible for the
candidates to take time to write their doctoral theses or ad­vance their career goals. Attendance at seminars and work­
shops on specific topics, as well as mentoring, promotepersonal and professional further development. At thesame time, we support networking with other beneficiaries
of programs like external scholarships at Fraunhofer ISE.

Shared knowledge: The library at Fraunhofer ISE
offers comprehensive services to researchers andall members of staff.

17

Facts and Figures

Doctoral Theses

Sven Auerswald“Dezentrale Fassaden­integrierte Wohnungslüftungsgeräte:
kombinierte Bewertung des erzielten Luftaustausches und derEnergieeffizienz” (Distributed façade-integrated apartment
ventilators: Combined assessment of the achieved air exchange
and energy efficiency), University of Freiburg, 2023
Varun Arya
“Laser Ablation of Dielectric Layers of Solar Cells”, University
of Freiburg, 2023
Oliver Fitz
“Entwicklung einer Zink­Ionen­Batteriezelltechnologie mit
wässrigen Elektrolyten für stationäre Anwendungen”(Development of zinc­ion battery cell technology with aqueous
electrolytes for stationary applications), University of Stuttgart,
2023
Sebastian Gamisch“Untersuchung eines Thermomanagementsystems für statio­
näre Batteriespeicher basierend auf Phasenwechselmaterialien”(Investigation of a thermal management system for stationary
battery storage based on phase­change materials), University
of Freiburg, 2023

ISE Research School

Gregor Gorbach“Internal Carbon Pricing and its Use for the Decarbonisationin Organisations Considering Price Uncertainties”, University ofFreiburg, 2023
Arne Groß“Stochastic Model Predictive Control for Smart Grid
Applications”, University of Freiburg, 2023
Katharina Gensowski“Low­temperature Front­side Metallization for Solar Cell
Applications Using a Parallel Dispensing Technology”,
University of Freiburg, 2023
Benjamin Hammann“The Influence of Hydrogen on Silicon Solar Cells: Investigating
the Link to Degradation Mechanisms”, University of Freiburg,
2023
Lotta Koch
“Energy Performance and Ecological Potential of Solar Thermal
Façade Collectors Made of Ultra-High-Performance Concrete(UHPC) for a CO2 Neutral Heat Supply”, Technical University of
Munich, 2023

In April 2023, Fraunhofer ISE founded the ISE Research School. The graduate
college has been created by the Institute to provide the best possible support
to its doctoral candidates during their education and to encourage inter­
departmental networking.
The program is open to all doctoral candidates at Fraunhofer ISE and encom­
passes the topics of research, teaching and interdisciplinary further education.
The ISE Research School offers a space for networking and interdisciplinary
exchange: It provides the framework for the ISE DOK Colloquium, which takes
place twice a year and is a platform for the doctoral candidates to present theirwork in the form of talks or posters. The program also includes lectures fromrenowned scientists: For example, the sustainability researcher, Prof. Arnim Wiek,
held an invited lecture on 24th October, 2023, as part of the Colloquium.

The 2nd ISE DOK Colloquium took placeon 24th October, 2023, in the Solar Info
Center in Freiburg.

18

As a longer­term perspective, Fraunhofer ISE expects that this structured pro­gram will further enhance the comprehensive education of doctoral candidates
and increase the attractivity of the Institute for future doctoral research projects.

Facts and Figures

Franz Mantei“Large­scale Production of Oxymethylene Dimethyl Ethers”,
Technical University of Berlin, 2023
Marius Meßmer“Development and Characterization of Resource­Saving
Doping Processes for Industrial Silicon Solar Cells”, University
of Freiburg, 2023
Jakob Metz
“Entwicklung und experimentelle Analyse eines Mehrquellen­
Wärmepumpensystems aus Erdreich und Außenluft” (Develop­
ment and experimental analysis of a heat pump system basedon both ground and external air heat sources), University ofFreiburg, 2023
Sebastian Roder“Laserbasierte Wärmebehandlung zur Wirkungsgradstabilisie­rung und ­steigerung von Solarzellen” (Laser­based thermal
treatment to stabilize and improve the efficiency of solar cells),
University of Freiburg, 2023
Stephan Schindele“Nachhaltige Landnutzung dank Doppelernte. Eine mehr­
dimensionale Politikanalyse der Agri­Photovoltaik­Diffusion in
Deutschland” (Sustainable land use thanks to a double harvest.
A multi­dimensional political analysis of the dissemination ofagri­photovoltaics in Germany), University of Tübingen, 2023
Patrick Schygulla“III­V­Semiconductor Subcell Absorbers in Silicon­Based Triple­
Junction Solar Cells”, University of Freiburg, 2023
Charlotte Senkpiel“Kopplung sozialwissenschaftlicher und individueller Aspek­
te mit Energiesystemmodellen: Theoretische Betrachtungen,Diffusion von Elektromobilität und Effekte regionaler Selbstver­
sorgungsziele auf das Stromsystem” (Coupling of sociologicaland individual aspects with energy system models: Theoreticalreflections, dissemination of electromobility and effect ofregional supply autonomy goals on the electricity system),
University of Freiburg, 2023
Maximilian Trommsdorff“Techno­Economic Analyses of Agrivoltaics: Approaches in
Arable Farming, Technology Choice, and Economic Perfor­
mance in Horticulture”, University of Freiburg, 2023

Jakob Ungerland“Äquivalente dynamische Modellierung aktiver Verteilnetze
mit netzfolgenden und netzbildenden Umrichtern” (Equivalent
dynamic modeling of active distribution grids with grid­reactive
and grid­forming inverters), University of Stuttgart, 2023
Natapon Wanapinit“Characterization of Operational Flexibility Resources and
Evaluation of Potential Utilization in Distributed Energy Sys­tems”, University of Freiburg, 2023
Zalma Zouhair“Perovskite Photovoltaic Devices: Charge
Selectivity of Carbon­Based Electrodes”, Abdelmalek Essaadi
University, Morocco, 2023

Professorships andLectureshipProf. Sonia Dsoke
W3 Chair for Electrochemical Energy Carriers and Storage
Systems at the Institute for Sustainable Systems Engineering(INATECH), University of Freiburg, 2023
Prof. Holger Neuhaus
W3 Chair for Materials Systems for Solar Energy Use at theFaculty of Engineering, University of Freiburg, 2023
Dr. Ralf Preu
Post­doctoral treatise, Lecturer for Sustainable Technical
Systems at the Faculty of Engineering, University of Freiburg,
2023
Dr. Peter Schossig
Appointment to the W3 Chair for Technologies for Climate­
Appropriate Buildings and Neighborhoods at the Faculty for
Architecture, Karlsruhe Institute of Technology, 2023

19

Facts and Figures

Prizes and Awards

Dr. Oliver Höhn
Consolidator Grant, research on highest-efficiency solar cells,
European Research Council (ERC)
Dr. Florian NestlerPeter and Luise Hager Prize 2023, Doctoral Thesis on “Dynamic
Operation of Power­to­X Processes Demonstrated by Methanol
Synthesis”, Karlsruhe Institute for Technology

Luis Eduardo AlanisIEEE PVSC, Best Poster Award, “Analysis of Thermal Behavior
and Reliability of Bare Die Diodes Embedded within PV
Modules as Bypass Devices”, IEEE PVSC Committee
Dr. Andreas Beinert
3rd Poster Prize, 38th PV­Symposium, “Bewertung von PV­An­
lagen für Wind­ und Schneelasten mit FEM­Simulationen”(Evaluation of PV systems for wind and snow loads with FEM
simulations)
Prof. Andreas Bett, Dr. Frank Dimroth
Research Prize of the Werner Siemens Foundation (WSS),
Finalists in the competition for the “Project of the Century”
Dr. Dmitry Bogachuk
Young Scientists’ Prize, Doctoral thesis on “Understanding and
Improving Perovskite Photovoltaic Devices with Carbon­based
Back­Electrodes”, Eva Mayr Stihl Stiftung
Dr. Juliane Borchert
Hertha Sponer Prize for research on new solar cell materials,
German Physical Society (DPG)
Dr. Katharina Braig, Dr. Thibaud Hatt,
Dr. Leonard Tutsch, Dr. Markus Glatthaar
Start­up BW Elevator Pitch 2023, Business Plan “PV2+”,
Start­up BW

Paul Schlegel
2nd Prize of the Stiftung Energieinformatik in the category “Best
M.Sc. Thesis”, “Charakterisierung und techno­ökonomische
Analyse von Verwertungspfaden für Sauerstoff als Nebenpro­
dukt der Wasserelektrolyse”, (Characterization and techno­eco­
nomic analysis of utilization routes for oxygen as a by­product of
aqueous electrolysis)
Paul Schlegel
Innovation Prize of the German Hydrogen and Fuel Cell Associa­
tion (DWV) e.V. in the M.Sc. category for the thesis, “Charakte­risierung und techno­ökonomische Analyse von Verwertungs­
pfaden für Sauerstoff als Nebenprodukt der Wasserelektrolyse”(Characterization and techno­economic analysis of utilizationroutes for oxygen as a by­product of aqueous electrolysis)
Dr. Yam Siwakoti
Prizewinner of the Fraunhofer­Bessel Research Award of
the Alexander von Humboldt Foundation

M.Sc. Prizes of the Verein zur Förderung derSolaren Energiesysteme e.V.
Johanna Aulich
M.Sc. thesis “Advanced IV Characterization Methods for Tri­
ple­Junction Solar Cells under Different Spectral Conditions“

Dr. Katharina Braig, Dr. Thibaud Hatt,
Dr. Leonard Tutsch, Dr. Markus Glatthaar
Freiburg Innovation Prize 2023, Business Plan “PV2+”, “Gal­vanikverfahren zum Ersatz von Silber durch Kupfer für Solar­zellenkontakte” (Electro­plating process to replace silver bycopper for solar cell contacts), Technologiestiftung BioMed
Freiburg

Mohamed Mahmoud
M.Sc. thesis “Tuning Crystallization for Highly Efficient Mono­lithic Perovskite Silicon Tandem Solar Cells“

Oliver Fischer
Student Award, “Spatially Resolved and Subcell­Selective
Implied Open­Circuit Voltage Measurements on Perovskite
Silicon Tandem Solar Cells”, EU PVSEC 2023

Ella Susann Supik
M.Sc. thesis “Electrical and Optical Defect Characterization of
Epitaxially Grown Silicon“

Benjamin Hammann
SiliconPV Award 2023, Best Paper “Understanding the Firing
Cooling Ramp’s Influence on Light and Elevated-TemperatureInduced Degradation in Silicon”

20

Anna Rothenhäusler
M.Sc. thesis “Control of Battery Systems in Industrial
Companies with Reinforcement Learning“

Nicolas Vollmar
M.Sc. thesis “Auslegung, Aufbau und Inbetriebnahme eines
100 kVA­Antriebsinverters für hybrid­elektrische Antriebs­
systeme in der Luftfahrt“ (Design, construction and commis­
sioning of a 100 kVA drive inverter for hybrid electric drive
systems in aviation)

Daten und Zahlen

Sustainability

As pioneers of the transformation to a renewableand efficient energy supply, we at Fraunhofer ISE havea strong sense of obligation with regard to sustainability. Our Institute strategy is thus guided by theprinciple of comprehensive sustainability. For us, thismeans integrating sustainability, step by step, into
our operation and the content of our work: into our
research and development projects, into our management of human resources and building projects, aswell as into operation and organization. To support
this process, we continually set ourselves new
goals and assess whether the measures taken weresuccessful.

Research and Development
Major societal challenges such as the energy transition demand
an interdisciplinary and often a transdisciplinary approach.
We at Fraunhofer ISE are thus working in numerous researchand development projects together with external partners oncomplete solutions for climate­neutral neighborhoods, munici­
palities and industrial real estate. To accompany these projects
scientifically still better, we will strengthen our sustainability
competences, create better links between internal and externalinterfaces and identify “blind spots” in R&D operation.
We position our work on solutions and decision bases forthe energy transition in the context of the United Nations‘
Sustainable Development Goals. In the following chapters, ourR&D projects with a specific focus on sustainability are identi­
fied by a symbol(from page 54).

Fraunhofer ISE uses the electricity from Germany’s first solar
cycleway canopy. The system is located near the Institute andthe Messe Freiburg (Freiburg Trade Exhibition site).

As an energy­intensive research institute, Fraunhofer ISE iscurrently developing a climate strategy, which includes a
reduction of the externally supplied electricity by 25 percent
until 2025 in comparison to the base year of 2019, among
other aspects. We aim to reach this goal by a combinationof reduced electricity consumption and on­site electricity
generation. For example, we will expand the capacity ofour photovoltaic systems by 2300 kWp and invest around
3.6 million euros to do so. We have introduced an energy
management system to monitor all measures: in 2023,
Fraunhofer ISE successfully absolved the relevant certification
process according to DIN EN ISO 50001:2018.
Our commitment is in line with the strategy of the Fraunhofer­
Gesellschaft. It is planning to make its research operation
climate­neutral by 2045 and has created the “Fraunhofer klima­
neutral” initiative to organize and implement the process. Alongthe path toward climate neutrality, the Fraunhofer­Gesellschaft
aims to reduce its CO2 emissions by 55 percent and compensate
unavoidable emissions by 2030, as a first step. To this purpose,its own operational emissions will be determined, and savings
potentials and areas for action identified.

Monitoring and Reporting
Operation and Organization
Sustainability for the operation of our Institute particularlytranslates into saving energy and successively transforming theoperation of our equipment and buildings to be more climate­friendly, with the ultimate goal of climate neutrality. During thepast two years, we have implemented processes to reduce ourconsumption of gas and electricity, for example, by introducing
energy­optimized processing sequences in our laboratories.

Fraunhofer ISE reports regularly on its sustainability activities
and also publishes data and process information in its sustain­
ability report, transparently and systematically according to
the standards of the Global Reporting Initiative. Our successful
participation in the Future Ranking of Sustainability Reports in
2021 that was organized by the German Institute for Ecological
Economy Research (IÖW), as well as our nomination for theGerman Sustainability Prize in July 2023 in the “Education andResearch” category, are incentives for us to continue the efforts
we have started in the direction of comprehensive sustainability.

21

Strategy and Business Areas 		

22

Strategy and Business Areas

Our newsletters offer
regular updates on our
research highlights.

Contents
Strengthening German and European Industry Increases Resilience . . . . . . . 24
New Organizational Structure and External Representation . . . . . . . . . . . . . 26
Toward Resilient, European Photovoltaic Production . . . . . . . . . . . . . . . . . . . 28
Business Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Photovoltaics: Materials, Cells and Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Photovoltaics: Production Technology and Transfer . . . . . . . . . . . . . . . . . . . . . .
Solar Power Plants and Integrated Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . .
Power Electronics and Grids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Climate­Neutral Heat and Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hydrogen Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

30
30
32
34
36
38
40
42
44

R&D Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Accredited Laboratories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

23

Strategy and Business Areas

Strengthening German and European
Industry Increases Resilience
A conversation with the Institute Directors,
Prof. Hans-Martin Henning and Prof. Andreas Bett

The corona pandemic, the ”gas crisis” and theimplementation of the energy transition all expose
how strongly Germany depends on international
suppliers. How critical is that?

Politics, the economy, media and society at large
have all grappled intensively with the implementation of the energy transition during the pastmonths. What effect did this have on the workof Fraunhofer ISE?
Bett: ”Our Institute has been working for many years on tech­
nological solutions for the successful implementation of theenergy transition. In that respect, it is positive for us when the
topic is increasingly present in politics and public debate. The
required technologies are fundamentally available but there
are still challenges to industrial implementation. Politics andregulatory bodies are now confronted with the demanding
task of setting the right boundary conditions.”
Henning: ”To be concrete, I would like to mention the topic
of heat pumps, which we have been researching for many
years, because we are convinced that this is a key technology
for the decarbonization of the heating sector. The revision of
the German building energy law meant that they were a major
focus of attention last year. However, it became evident that it is
not simple to introduce this type of technology, which basicallyfunctions well, to a broad market. Fraunhofer ISE can support
the process by developing appropriate solutions that can beeasily integrated into different applications such as in apartmentbuildings.”
24

Bett: ”We have a certain degree of global dependence in almost
all technologies, but a critical aspect is that this is increasingly
focused on China. This is why the aspect of resilience in the tech­
nological sector is now so important as a basis for realizing theenergy transition. We need to analyze exactly where components
and products originate for each individual case. Can they bepurchased in three or four countries on the global market or onlyone? The most prominent example is photovoltaics. 99 percentof the silicon wafers required for PV modules are manufactured
in China. This means that a very critical dependence exists
throughout the world, but it also offers a chance for establishing
PV production in Europe. By contrast, when we look at heatpumps, there is indeed also a strong dependence on Asia forrefrigerant compressors, but distributed over several countries
in this case. For battery cells, where there is currently a strong
dependence on China, important technological know­how still
existed in Germany, and even more importantly, the political will
to re­establish production again here in Germany. In building
up production capacity, it is not always absolutely necessary tomaintain distance from China; it is also possible to move forward
together in cooperation.”

Are there other technologies which should also be
observed critically?
Henning: ”At present, we must be particularly watchful concern­
ing hydrogen. Here, we are still in an earlier phase of market
development. The course must be set correctly now and know­
how must be established in Germany and Europe to gain tech­
nological competence or even leadership, and avoid creating
critical dependence. Great opportunities open up if the expan­
sion is secured by flanking political measures. Technologicaldevelopment functions particularly well if it is used directly
by local markets, such that application and upscaling can be
implemented within the country. As a general principle, I findit important not to aim for autonomy. That cannot succeed,
because even if the manufacturing technology is located here,Strategy and Business Areas

we are still dependent on delivery of raw materials. Thus, thetopic of resilience should be viewed more broadly: Diversi­
fication of delivery sources and supply chains as well as
technological sovereignty for key technologies. This means
having access to important competences in Europe – not onlyin science but also in the economy – so that we can continue
to act independently.”

How can Fraunhofer ISE concretely support
local industry in these efforts?
Bett: ”Technologically, Fraunhofer ISE has driven developments
forward in many areas and is at the global forefront. We draw
on extensive experience. Now it is important to cooperatewith industry to organize the transfer. That means that we
can certainly support industry very well in answering current
technological questions, but also to some extent in developing
business models, and we can organize networking, which isvery important if the goal is to build up major enterprises.”

Are there further aspects which offer
advantages for local industries?
Henning: ”Advantages exist, for example, in integrated
photovoltaics. Modules for these applications are producedin smaller series, which are optimized for the specific demands
in buildings or in agriculture. Here, value will naturally becreated primarily in the local region. It is also obvious thatcomplete solutions for a specific location are usually bestdeveloped locally. One example is the development of climate
neutrality for production sites. This is a direction which we aim
to support specifically with our newly created cross­sectional
topic of ”System Integration” at the Institute. This can draw
on all the competences that are distributed over the entire
Institute, to develop customized solutions for commercial
customers – for example, the housing sector or managers ofindustrial real estate.”

Henning: ”We have also re­organized ourselves at theInstitute, with the goal of implementing complete solutions
yet more effectively and successfully. For example, the topics
of PV power plants, power electronics and battery storage
are now all gathered together into the newly created Power
Solutions Division so that the key competences for the elec­
tricity transition can be combined at the technological level.”

How can European manufacturers compete
successfully on the international market, alsowith regard to the often lower prices in Asia?
Bett: ”'Cheap production' often means that there is no pricetag on factors such as CO2 emissions and their effect on the
climate or on social aspects such as humane working condi­
tions, such that the true costs are not reflected. Awarenessof these aspects must certainly still be more widely anchoredin our society. At Fraunhofer ISE, we have decided to address
the topic of sustainability holistically and strategically. Thus,
we have intensified our efforts to study lifecycle analyses andall related dependences, which are indeed very complex. We
are basing our research on this principle. In addition, we aim
to develop technologies such that they are fit for a circular
economy.”Henning: ”Another aspect is that automation has not exhaust­
ed its potential. Our aspiration is to apply modern digitalization
processes, including artificial intelligence methods, to theentire value chain, in order to access cost reduction potentials.
A further important aspect is reducing the consumption of
resources. We want to cooperate with industry in developing
processes which require the smallest possible amounts ofenergy and materials and aim to re­use all components andmaterials completely – and this without increasing costs, if
possible.”

The Institute Directors, Prof. Andreas Bett (left)
and Prof. Hans-Martin Henning (right).

Which concrete initiatives has Fraunhofer ISE
planned for next year?
Bett: ”It is still important for us to develop individualcomponents further and to be at the forefront of tech­
nological development. But we want to offer more com­prehensive, customer­oriented system solutions. We are
well prepared for this as an Institute because we have sucha broad base of competences. Beyond that, we can draw
on our network within the Fraunhofer­Gesellschaft and withother research organizations. That is an aspect which ourclients value highly. The sustainability goal will also be central
for our R&D work. We thus see Fraunhofer ISE well prepared
for the future.”25

Strategy and Business Areas

New Organizational Structureand External Representation

The energy transition demands comprehensive restructuringof the energy supply, from its sources through distribution andstorage up to utilization. For many decades, Fraunhofer ISE
has participated in the technological development of key
components for this conversion of the energy system, rang­
ing from solutions for photovoltaics through grid technology
and power electronics, electric and thermal energy storage,
technology to generate and use hydrogen up to heat pumps.
Technological further developments to improve performanceand lower costs will continue to play an important role infuture, whereby questions concerning sustainable productionand efficient use of resources will become more significant.
Sustainability is thus a core element of our Institute strategy.
On the one hand, that means that sustainability aspects will
be taken into account from the beginning of research anddevelopment work, and on the other hand, that the operationof our Institute itself will be continually developed further toreduce its effect on the climate and the environment.
As the level of technological development maturity increases,
practical implementation is gaining enormously in importancefor the success of the energy transition. For instance, politicaldecisions have recently created the framework for restructur­
ing the supply of heating in the building sector, which willlead to an accelerated implementation of new solutions. The
further incorporation of renewable energy sources for electri­
city generation also has appreciable effects on electricity grids.
Systemic solutions, including power electronics and storage at
different grid levels are thus needed to guarantee a stable and26

reliable electricity supply in future. To meet these challenges
optimally, we have adapted our organizational structure andcreated four large scientific Divisions:Photovoltaics(Leadership: Prof. Stefan Glunz, Dr. Ralf Preu)
Power Solutions(Leadership: Dr. Harry Wirth)
Heat and Buildings(Leadership: Dr. Peter Schossig)
Hydrogen Technologies(Interim leadership: Ulf Groos, Dr. Achim Schaadt,
Dr. Tom Smolinka, Robert Szolak)
In the Photovoltaics Division, cell and module development
are now located under one roof. The grouping of photovoltaic
power plants with power electronics, grid technology andbattery storage technology in the Power Solutions Division
strengthens our offer for systemic solutions for future supplyof electricity. In the Heat and Buildings Division, we offer com­prehensive solutions for the heating transition. The Hydrogen
Technologies Division addresses the complete range of ques­
tions from the dynamically developing industry in this sector.
This structure harmonizes excellently with the missions of”Electricity Transition”, ”Heating Transition” and ”Hydrogen”
propagated in the recently published, eighth energy research
program of the German Federal Ministry for Economic Affairs
and Climate Action (BMWK).

Strategie und Geschäftsbereiche

Fraunhofer ISE develops complete solutions for climate-neutral buildings, neighborhoods and municipalities. The photo shows
the Gutleutmatten quarter in Freiburg, where distributed solar thermal systems were integrated into the local heating network.

In addition, we have developed a new structural element withthe program line “Overarching System Integration”, which
will be led by Prof. Christof Wittwer. In this cross-sectional
unit, comprehensive solutions for robust future energy supply
systems will be researched, drawing on the know-how of thefour more technologically oriented Divisions, and developed incooperation with clients.
With this unit, we are reacting to the increasing demand fromthe economy and the public sector for complete solutions forclimate-neutral buildings, neighborhoods, municipalities andindustrial real estate, and will accompany implementationfrom concept development up to operation optimization,
holistically and scientifically, in living laboratories anddemonstration projects.
We have also reorganized our Business Area structure toachieve better customer orientation. This Annual Report
is structured according to the eight new Business Areas,
which form the basis of our external representation from
1st January, 2024:
Photovoltaics – Materials, Cells and Modules
Photovoltaics – Production Technology and Transfer
Solar Power Plants and Integrated Photovoltaics
Power Electronics and Grids
Electrical Energy Storage
Climate-Neutral Heat and Buildings
Hydrogen Technologies
System Integration

From 2024, Fraunhofer ISE is structuring its external
representation according to eight new, marketoriented Business Areas.

27

Strategy and Business Areas

Toward Resilient, European
Photovoltaic Production

The European Commission stated the goal clearly in
its "Net Zero Industry Act" (NZIA): In the photovoltaic
sector, 40 percent of the capacity required in 2030
should be produced in Europe. Expansion of photovoltaic production is being promoted accordingly andthe European solar industry is attempting to regain its
former strength. At Fraunhofer ISE, we are accompanying this process with our expertise and are working
closely with our industrial partners to strengthen
existing production capacities and to establish new
ones. For more than 20 years, we have supported
European manufacturers of solar cells and modules
with our know-how. In 2018, Fraunhofer ISE demanded retention of technological sovereignty in a White
Paper. "In our view, it is necessary, also for reasons ofself-reliance and political independence, to establish
photovoltaic production and operate the complete
value chain in European", summarizes one of theInstitute Directors, Prof. Andreas Bett.

Creating Favorable Political Boundary Conditions
However, the boundary conditions are difficult, as China
dominates both the PV market and the value chain for silicon
photovoltaics, which accounts for more than 95 percent of
the photovoltaic market. If this dependence is to be reduced,
it is necessary to create political boundary conditions whichallow fair competition. Thus, the European associations, theEuropean Solar Manufacturing Council (ESMC) and Solar
Power Europe (SPE) are jointly active within the ESIA Initiative(European Solar Photovoltaic Industry Alliance) in demanding
European PV production along the value chain. Also, theGerman industrial association, Bundesverband Solarwirtschaft,
has prepared a proposal: It proposes resilience bonuses aspart of the German Renewable Energy Act (EEG) payments,
which could be higher, depending on the share of European
production.
Numerous measures will be needed to locate important
technologies and production lines in Europe and thus build
up greater resilience for the conversion of the energy system.

The Center for High Efficiency Solar Cells
at Fraunhofer ISE in Freiburg.

28

Companies along the PV value chain in Europe.

Fraunhofer ISE – Partner for Industry
Fraunhofer ISE is already supporting manufacturers intensively
now with R&D services and cooperates with businesses which
are building up production capacity. For example, we will
support the HoloSolis company with technology selection andfactory planning during the conceptional design and building
phase, on the basis of a strategic cooperation agreementthat was signed in summer 2023. The company is planningto build a production line for PV solar cells and modules near
the French­German border. Production is planned to start in
2025 and to produce five GW per year when operating at full
capacity.
Furthermore, we are conducting research on a new generationof solar cells and developing module designs that will make
Europe competitive. We support manufacturers of modules
and production equipment in our well­equipped, modern
production laboratory, Module­TEC, in which we can fabricate
a wide variety of module sizes and designs and design each
module individually. Together with the company, Heckert Solar
GmbH, we have developed a PV module based on M12 half­cells with an efficiency of 20.5 percent. Fraunhofer ISE wasresponsible for the conception, preliminary development andthe production of the first module prototypes.
The sustainability of production is particularly important to
us at Fraunhofer ISE, i.e. we aim to reduce the energy con­sumption and make efficient use of raw materials. Success inre­establishing European photovoltaic production depends
decisively on the availability of critical raw materials. Thus, wehave anchored circular value creation as a goal in our Insti­
tute strategy. This encompasses the re­use of materials andcomponents as well as feeding back into material cycles. Our
goals are illustrated well by three spin­offs from the Institute:
The NexWafe company addresses the market for high­quality
wafers and has set itself the goal of upscaling the EpiWafer
technology. The HighLine Technology GmbH enables resource­
conserving application of pastes for cell metallization with its
proprietary dispensing technology. The PV2+ start­up has com­menced operation successfully with an electro­plating process
to replace silver for solar cell contacts by copper.
Outlook
There are high expectations on the European Commission
and the national German government to support the produc­tion of photovoltaics along the value chain. Fraunhofer ISE is
accompanying this initiative and is thus expanding its capa­
city for module development in Module­TEC. At the end of
February 2024, we will open our new production laboratory
in the former Solarfabrik in Freiburg. Four million euros were
invested in the site to establish existing and new production
facilities for connection technology and lamination in a factoryhall. This will allow us to support industrially relevant researchon series production of solar modules still more efficiently andthus contribute to the establishment of resilient photovoltaic
production in Europe.

29

Strategy and Business Areas

Photovoltaics: Materials, Cells
and Modules
Market Position

LeadershipHigh conversion efficiencies and the resulting low levelized costs Prof. Dr. Stefan Glunz, Phone +49 761 4588­5191
of photovoltaic electricity can only be achieved with optimal andcost-efficient materials. For silicon, organic, III-V and perovskite
Topics in this Business Area
semiconductors, we achieve very good electronic properties
by in­depth analyses and optimized processes. Based on theseresults, we apply simulation tools to optimize solar cell archi­
Silicon Material and Semiconductor Substrates
tectures and implement these in our laboratories. This leads topathbreaking cell architectures such as the TOPCon silicon solar Dr. Charlotte Weiss, Phone +49 761 4588­5591
cell, which we developed and which has become established as
Silicon Solar Cells and Modules
an industrial standard throughout the world.
Dr. Ralf Preu, Phone +49 761 4588­5260
As the silicon solar cell is approaching its theoretical efficiency
Silicon-Based Tandem Solar Cells and Modules
limit, we are developing the next solar cell generation on thebasis of multiple­junction solar cells. In doing so, we apply ourDr. Martin Hermle, Phone +49 761 4588­5265
many years of experience with III­V semiconductors to produce
promising tandem solar cells with new and potentially more
Perovskite Thin-Film Photovoltaics
cost­effective semiconductors such as perovskites. For module
Dr. Markus Kohlstädt, Phone +49 761 203­96796
manufacturing, we are promoting new topologies such as
matrix shingling which produces particularly aesthetically attrac­ Organic Photovoltaics
tive results in combination with our MorphoColor® technology. Dr. Uli Würfel, Phone +49 761 203­4796
In addition, we are conducting research on tandem modules,
which enable the highest module efficiencies in fixed installaIII-V Solar Cells, Modules and Concentrator Photovoltaics
tions or in tracking systems with concentration.
Dr. Frank Dimroth, Phone +49 761 4588­5258
Photonic and Electronic Power Devices
Dr. Henning Helmers, Phone +49 761 4588­5094

Facts and Figures
Total staff

165

Journal articles and contributions to books

84

Lectures and conference papers

90First patent applications

30

3

Photovoltaics: Materials, Cells and Modules”

We are opening the door to the next generationof photovoltaics with the development of
perovskite-silicon multiple-junction solar cells.”

Maryam Heydarianand Mina Heydarian
Ph.D. candidates working on
perovskite­silicon multiple­
junction solar cells.

More Information
Business Area

Publications

Projects

31Strategy and Business Areas

Photovoltaics: Production Technology
and Transfer
Market Position

Leadership

Sustainable production of photovoltaic components requires
comprehensive knowledge of their operating principles andmanufacturing – this is where our expertise on production
technology plays its role. The numerous production techno­
logies currently in use include wet­chemical processes, epitaxial
procedures to produce materials or laser and printing processes
for solar cell manufacture. Coating processes are also applied
for module production as well as connection and lamination
technologies. The application of processing and characterizationequipment must guarantee high performance, reproducibility
and yield for the production of high-efficiency solar cells andmodules.

Dr. Ralf Preu, Phone +49 761 4588­5260

In our large­scale laboratories, we develop innovative approach­es from the proof of concept up to feasibility demonstrations insmall series with well­established and novel production equip­
ment. Our techno­economic and ecological approaches provide
the basis for well­founded investment decisions for industrial
manufacturers concerning e.g. the selection of photovoltaic
components and the resulting necessary materials and equip­
ment. These analyses also form the basis for our technology
transfer to current and future manufacturers of photovoltaic
components. Our experienced scientists and engineers support
our partners hereby with services ranging from feasibility studies
to production.

32

Material Technologies
Dr. Charlotte Weiss, Phone +49 761 4588­5591
Metrology and Simulation
Dr. Martin Schubert, Phone +49 761 4588­5660
Coating Technologies andHigh-Temperature Processes
Dr. Marc Hofmann, Phone +49 761 4588­5051
Wet and Dry Chemical Processes
Dr. Martin Zimmer, Phone +49 761 4588­5479
Laser and Printing Technologies
Dr. Jan Nekarda, Phone +49 761 4588­5563
Interconnection and Encapsulation Technologies
Prof. Holger Neuhaus, Phone +49 761 4588­5825
Artificial Intelligence and Data Management
Dr. Stefan Rein, Phone +49 761 4588­5271

Facts and Figures
Total staff

313

Journal articles and contributions to books

84

Lectures and conference papers

90First patent applications

Topics in this Business Area

2

Technology Assessment and Transfer
Dr. Jochen Rentsch, Phone +49 761 4588­5199

„Photovoltaics: Production Technology and Transfer

Our extremely productive and mild laser processes
enable the efficient application of widely available
and cost-efficient materials in PV production.”

Jan Paschen and Anna Münzer
Ph.D. candidates working on
laser­processing technology.

More Information
Business Area

Publications

Projects

33

Strategy and Business Areas

Solar Power Plants andIntegrated Photovoltaics
Market Position

Leadership

We conduct research so that innovative, high­quality and
Dr. Anna Heimsath, Phone +49 761 4588­5944
cost­effective solar systems become established on all suitablesurfaces. To this purpose, we develop methods and technologies
Topics in this Business Area
for all aspects of PV modules and solar power plants and theirapplications. The integration of solar technology into the urban
space, into transport infrastructure and on agricultural andModule Analysis and Reliability
water­covered areas exploits an enormous additional potential
area. Due to the large share of energy from renewable sources, Daniel Philipp, Phone +49 761 4588­5414
solar performance prediction is becoming increasingly impor­
Photovoltaic Solar Power Plants
tant. We are thus developing prediction models for reliable
Dr. Anna Heimsath, Phone +49 761 4588­5944
forecasts, depending on the PV usage duration and the area
occupied by PV.
Integrated Photovoltaics
Dr. Harry Wirth, Phone +49 761 4588­5858
We guarantee comprehensive quality assurance, following
the phases of Fraunhofer ISE’s quality cycle – Development,
Solar Thermal Power Plants
Engineering, Procurement, Commissioning und Operation.
Dr. Gregor Bern, Phone +49 761 4588­5906
With our simulation tools, we investigate the potential andfeasibility of new technologies, taking site-specific and climatic
Solar Energy Meteorology
factors into account. Our team characterizes the performance
Dr. Elke Lorenz, Phone +49 761 4588­5015
of new module technologies and tests their reliability in thelaboratory and in the field. Our services also cover solar-thermal
power stations and their combination with photovoltaics andpower­to­X technologies.

Facts and Figures

34

Total staff

145

Journal articles and contributions to books

22

Lectures and conference papers

64Solar Power Plants and Integrated Photovoltaics”

Double usage of land areas offers manifold options
to agriculture, industry and municipalities for local
electricity generation.”

Dr. Anna Heimsath, Business Area Leader for Solar
Power Plants and Integrated Photovoltaics, andOliver Hörnle, project leader for agri­photovoltaics.

More Information
Business Area

Publications

Projects

35

Strategy and Business Areas

Power Electronics and Grids

Market Position

Leadership

The integration of renewable energy into our energy system
is increasing – and thereby the electrification of energy supply
in the electricity, heat and mobility sectors. Along the pathway
from generation to final use, electricity passes through numerous power-electronic conversion steps. As a result, the expan­
sion of renewable energy is accompanied by the dissemina­tion of electricity inverters and digital systems in all market
segments.

Christian Schöner, Phone +49 761 4588­2078

With the help of the most modern components and tech­
nologies – e.g. on the basis of SiC and GaN semiconduc­tors – essential advantages can be realized at the systemlevel. These are urgently needed to reach the goals set for
the energy transition with the available and exploitable raw
material resources. Interoperability, digitalization and modelingof energy systems is also becoming increasingly important. In
a decentrally organized electricity grid without conventional
power plants, inverters will be responsible for system stability
in future. However, also the extension of loads with grid­sup­portive functions and energy management will play a greaterrole. We support our industrial partners on these topics bothwith our expertise and also with our infrastructure in the“Center for Power Electronics and Sustainable Grids”.

Facts and Figures
Total staff

36

102

Journal articles and contributions to books

5

Lectures and conference papers

24

Topics in this Business Area
Power Converters
Stefan Reichert, Phone +49 761 4588­5476
High-Power Electronics and System Engineering
Andreas Hensel, Phone +49 761 4588­5842
Smart Metering and Grid Control
Marco Mittelsdorf, Phone +49 761 4588­5446
Grid Planning and Operation
Dr. Bernd Wille­Haußmann, Phone +49 761 4588­5443
Converter-Based Power Grids and System Stability
Roland Singer, Phone +49 761 4588­5948

Power Electronics and Grids”

We conduct research on important key
technologies for successful sector coupling.”

Philipp Ernst, manager of the
Verbundnetz Stabil project, andFranziska Hans, scientist.

More Information
Business Area

Publications

Projects

37

Strategy and Business Areas

Electrical Energy Storage

Market Position

Leadership

The energy transition and a sustainable transformation of themobility sector can succeed only with the help of safe, reliable
and high­performance battery storage units. The demand forcorresponding battery technologies will thus increase expo­
nentially. To achieve the stated goals, a sustainable circular
economy will also be needed, as is addressed in the European
Battery Regulation. Digitalization plays a central role within
this context in the production, utilization phase and end­of­life(EOL) areas.

Dr. Daniel Biro, Phone +49 761 4588­5600

The specifications on battery management systems that are
defined as part of the battery passport – e.g. concerningtransparency about the state and remaining lifetime – are also
drivers of this development.
In our “Center for Electrical Energy Storage”, we are research­ing the next generation of lithium­ion batteries and promisingalternatives such as zinc­ion or sodium­ion technologies. Weview the entire value chain – from materials and cells throughbattery systems technology up to diverse storage applications.
The laboratory infrastructure in the Haidhaus in Freiburg allows
us to offer extensive scientific tests at the cell and systemlevels, as well as modern characterization procedures.

Facts and Figures
Total staff

38

88

Journal articles and contributions to books

4

Lectures and conference papers

26First patent applications

2

Topics in this Business Area
Battery Management and Cells
Dr. Lea Eisele, Phone +49 761 4588­2585
Battery Engineering
Dr. Nina Kevlishvili, Phone +49 761 4588­2042
Production Technology for Batteries
Marc Kissling, Phone +49 761 4588­5046
Battery Integration and Operational Management
Nils Reiners, Phone +49 761 4588­5281
Technology Evaluation for Batteries
Manuel Bergmann, Phone +49 761 4588­2818

Electrical Energy Storage”

Batteries are a central key to a sustainable
and reliable electricity supply.”Dr. Moritz Kroll, deputy leaderof the “Battery Testing Lab”, andDr. Lea Eisele, leader of the Battery
Cell Technology group.

More Information
Business Area

Publications

Projects

39

Strategy and Business Areas

Climate­Neutral Heat and Buildings

Market Position

Leadership

The changeover to renewable energy carriers is becoming
increasingly urgent, not only to protect the climate but also
to ensure supply and price stability. In the building sector,
the specific challenge is to provide technical and systemic
solutions which address a wide bandwidth of actors. Possible
solutions include technology for non­fossil heat generation,transformation concepts for the housing sector, industry andcommerce, and heat supply, as well optimization of the pro­
cesses by digitalization. In the construction sector, productivity
can be raised only by standardization and digitalization of thebuilding processes, such as the standardized PV modules that
we are developing for façade integration.

Sebastian Herkel, Phone +49 761 4588­5117

In order that an accelerated uptake of heat pumps with naturalrefrigerants can succeed in the building sector, we are techno­
logically supporting the development of optimized refrigerant
circuits and ensure quality by laboratory and field tests. We also
develop cooling circuits and exploit new heat sources to enable
increased utilization of large and high­temperature heat pumps
for heating networks and industrial applications. Furthermore,
we work on integration of the equipment into each specificapplication.

Topics in this Business Area
Building System Technology
Dr. Peter Engelmann, Phone +49 761 4588­5129
Operational Management for Buildings,
Properties and Industry
Nicolas Réhault, Phone +49 761 4588­5352
Building Envelopes
Dr. Bruno Bueno, Phone +49 761 4588­5377
Heat Pumps
Dr. Marek Miara, Phone +49 761 4588­5529
Hot and Cold Storage
Dr. Sebastian Gamisch, Phone +49 761 4588­5468
Ventilation, Air-Conditioning, Refrigeration
Dr. Lena Schnabel, Phone +49 761 4588­5412
Water Treatment and Materials Separation
Dr. Joachim Koschikowski, Phone +49 761 4588­5294

Facts and Figures
Total staff

221

Journal articles and contributions to books

29

Lectures and conference papers

37First patent applications

40

1

Solar Thermal: Systems and Components
Dr. Korbinian Kramer, Phone +49 761 4588­5139

Climate-Neutral Heat and Buildings”

Hannes Seifarth,technician, andPhilipp Bauer,scientist.

We ensure the quality and efficiency of heatpumps with natural refrigerants by prototype
development and testing.”

More Information
Business Area

Publications

Projects

41

Strategy and Business Areas

Hydrogen Technologies

Market Position

Leadership

The global community intends to cease its emission of CO2 by
2050 – this goal pushes hydrogen as a fuel into the limelight,
as sustainably produced hydrogen and its derivates can replacefossil fuels. The enormous bandwidth of application possibili­ties for hydrogen as an energy carrier and storage medium,
as well as a fundamental chemical, is now developing its
huge potential.

Ulf Groos, Phone +49 761 4588­5202

Appreciable innovations are still necessary to achieve therequired upscaling of the hydrogen economy, as the tech­
nological and commercial development of central elementsof the value chain are currently in an early industrial phase.
Thus, contributions from research and development – fromfundamental materials questions up to innovative, scalable
production processes – are needed to retain opportunities
for German industry at all stages of the value chain.
With our expertise, we accompany industrial partners andclients in the development of efficient technology along theentire value chain. In addition, we carry out lifecycle andtechno­economic analyses, in which we can develop andevaluate solutions for the production of hydrogen, its
efficient storage and customized distribution.

Facts and Figures

42

Total staff

174

Journal articles and contributions to books

13

Lectures and conference papers

21First patent applications

4

Topics in this Business Area
Fuel Cell
Ulf Groos, Phone +49 761 4588­5202
Electrolysis and Hydrogen Infrastructure
Dr. Tom Smolinka, Phone +49 761 4588­5212
Sustainable Synthesis Products
Dr. Achim Schaadt, Phone +49 761 4588­5428

Hydrogen Technologies”

Our goal is large-scale production of PEM electrolysers. We are cooperating with national and international partners to reach this goal.”

Richard Lohmann, engineer
in the HyFab project, and
Dr. Zohreh Kiaee, project
leader for fuel cell production.

More Information
Business Area

Publications

Projects

43

Strategy and Business Areas

System Integration

Market Position

Leadership

System integration plays a central role in the targeted transi­tion of our energy supply to a net­zero energy system. Many
components to provide emission­free energy are indeed
competitive today – but their integration into a complete,trans­sectoral energy system is still a great challenge. The heat,electricity and mobility sectors will need to interact increasing­
ly in future. This applies equally well to the energy supply ofbuildings and neighborhoods as to the establishment of inter­regional infrastructure to provide primary energy.

Prof. Christof Wittwer, Phone +49 761 4588­5115

Intelligent systems integration takes the current situation into
account: The large number of small PV systems places highdemands on supply reliability; in addition, grid infrastructure
should remain affordable. Here, flexibly controllable loads
and the application of storage units, for instance in electricvehicles that can feed charge back into the grid, can interact
in a digitalized operation management system. In the storageof renewably generated energy via intelligent control concepts,
there is a high utilization potential for the coupling of the elec­
tricity and heat sectors. Further important concepts include theapplication of hydrogen by electrolysis for longer­term storageof energy and its reconversion into electricity. We researchand develop corresponding solutions for the concrete energy
transition in the local area and test them together withpartners in living laboratories.

Topics in this Business Area
Energy System Analysis
Dr. Christoph Kost, Phone +49 761 4588­5750
Integrated Energy Infrastructures: Electricity,
District Heat, Gas
Prof. Christof Wittwer, Phone +49 761 4588­5115
Energy Data Analysis
Nicolas Réhault, Phone +49 761 4588­5352
Flexibility Management of Energy Systems
Dr. Matthias Kühnbach, Phone +49 761 4588­2373
Climate-Neutral Industry
Dr. Thomas Fluri, Phone +49 761 4588­5994
Climate-Neutral Cities, Urban Districts and
On-Site Systems
Dr. Annette Steingrube, Phone +49 761 4588­5062
Electric Mobility
Dr. Robert Kohrs, Phone +49 761 4588­5708

Facts and Figures
Total staff

83

Journal articles and contributions to books

15

Lectures and conference papers

53

First patent applications

44

Living Labs
Gerhard Stryi­Hipp, Phone +49 761 4588­5686

1

System Integration”

We are conducting research on systems integration
which brings all system components together in adigitalized grid infrastructure.”

Fabian Ernsting, B.Sc. candidate, andPhillip Pütz, scientific student assistant.

More Information
Business Area

Publications

Projects

45

Strategy and Business Areas

R&D InfrastructureFraunhofer ISE is equipped with excellent technical infrastruc­ture. Laboratories with a floor area of 22,300 m2 – including
900 m2 of clean­room area – and extremely modern equip­
ment and facilities are the basis for our competence in researchand development. Our goal is to access promising technologi­
cal solutions and transfer these into the economy and society.
Our industrial partners profit from the know-how of our staff
as well as the continuous expansion of our technical infrastruc­ture. Particularly small and medium­sized enterprises without
their own R&D departments gain access to high­performancelaboratory infrastructure and excellent research achievementsby cooperating with Fraunhofer ISE.
In its seven accredited laboratories, the Institute offers diverse
testing and certification procedures to commercial enterprises
and scientific institutions. At present, the Institute has two
calibration and five test laboratories with extremely modern
technical equipment, which are accredited by the Deutsche
Akkreditierungsstelle DAkkS (German Accreditation Body)(see p. 48 ff.).
In our eight laboratory centers and four production­relevant
technological evaluation centers, we develop new products,
processes and services and optimize existing ones.

Technological Evaluation Centers
SiM­TEC – Silicon Materials Technology Evaluation Center

PV­TEC® – Photovoltaic Technology Evaluation Center

Module­TEC – Module Technology Evaluation Center

Con­TEC – Concentrator Technology Evaluation Center46

R&D Infrastructure

Laboratory Centers
Center for High Efficiency Solar Cells

Center for Organic and Perovskite Photovoltaics

Center for Functional Surfaces

Center for Outdoor Performance

Center for Power Electronics and Sustainable Grids

Center for Electrical Energy Storage

Center for Heating and Cooling Technologies

Center for Electrolysis, Fuel Cells and Synthetic Fuels

Quality control of ashingling process.

47

Strategy and Business Areas

AccreditedLaboratories

Calibration of Solar Cells
In CalLab PV Cells, we offer calibration services for a diverse
range of PV cell technologies. The laboratory is accredited forsolar cell calibration by the Deutsche Akkreditierungsstelle
DAkkS (German Accreditation Body) and is as one of theinternationally leading photovoltaic calibration laboratories. In
cooperation with PV manufacturers, and with the support of
the German Federal Ministry for Economic Affairs and Climate
Action (BMWK), we work continuously on improving measure­ment tolerances and developing methods to measure newsolar cell technologies accurately.
In recent years, we have further expanded our measurement
facilities and can thus calibrate modern silicon solar cells up
to an edge length of G12 very accurately. For several years,
we have been working on measurement methods to deter­mine realistic performance parameters for perovskite­basedsolar cells. We can thus carry out measurements for perov­
skite­Si tandem solar cells up to an edge length of M10. Thisis based on our many years of experience specifically in thearea of III­V tandem solar cells. Primarily space, concentrator,and laser power conversion cells are at the focus of thesemeasurements.
In addition, we are supporting the development of standards
on concentrating and non­concentrating photovoltaics in theworking groups WG 2 and WG 7 of technical committee
TC 82 of the IEC.
Silicon, Thin-Film, Perovskite, Organic Solar Cells
Dr. Jochen Hohl­Ebinger
Phone +49 761 4588­5359
Wendy Schneider
Phone +49 761 4588­5146
Multi-Junction and Concentrator Cells
Dr. Gerald Siefer
Phone +49 761 4588­5433

cells@callab.deCharacterizationof a laser power
conversion cell.

48

Accredited Laboratories

Calibration of PV Modules

Quality Assurance of PV Modules

CalLab PV Modules is the only accredited calibration laboratory
for photovoltaic modules in Germany. Here, we calibrate PV
modules for production lines accurately, quickly and reliably.
In contrast to a classic measurement service, a calibration is
distinguished by highest demands on measurement uncer­
tainty and traceability. With an international record measure­ment uncertainty of only 1.1 %, confirmed by the Deutschen
Akkreditierungsstelle DAkkS (German Accreditation Body), we
calibrate reference objects for module manufacturers and thus
provide the references for production quantities on the GW
scale. Our calibration certificates and calibration marks on themodules stand for the highest accuracy and quality.

TestLab PV Modules tests the quality and reliability of PV
modules. Our accredited laboratory is equipped with modern
and innovative testing facilities that can be used for applica­
tions that extend well beyond standard testing procedures.

The expansion of our accreditation scope to include bifacial
and large­format modules complements the previous productportfolio and provides an important pillar for quality assuranceof future module technologies. High-efficiency cell techno­
logies such as PERC, TOPCon and HJT are currently in theportfolio of almost all module manufacturers, as are bifacial
technologies. Continuous development of new measurement
methods and adapted measurement equipment in our calibra­tion laboratory ensure that we can offer accurate power mea­
surements for these PV modules. A central element in verifying
and validating the measurement results is the stable calibrationlevel over many years, which ensures reliability and certainty
for our clients and project partners.

We advise our clients on cost-effective and time-efficienttesting programs and individual quality criteria. In cooperation
with our partner, VDE, we offer product certification according
to international standards.
The field of new cell and module concepts is very dynamic
at present. Modules are becoming larger and generate more
power, and the diversity of cell and connection concepts isincreasing. Divided cells, shingle technology with and without
connectors, multi­wire and tandem technologies play a promi­
nent role here. The application areas are also constantly being
developed further: Building or vehicle integration demands
new boundary conditions for module testing. Often, the speci­
fications in existing standards are not yet clear concerning thetesting of such modules. We thus investigate the applicabilityof testing and measurement procedures for these technologies
at an early phase and develop adapted methods. In doing so,
we follow the goal of greatest accuracy and practical rele­vance. We contribute our experience and results within inter­national standardization bodies.
Daniel Philipp

Phone +49 761 4588­5414

In addition, we are preparing methods to characterize modules
that are based on next-generation, high-efficiency cell technologies such as perovskite­silicon tandem solar cells. We mea­
sure the power output from concentrator PV modules understandard conditions using several outdoor test rigs equippedwith trackers or in our laboratory with a solar simulator.
Martin Kaiser

Phone +49 761 4588­5786

tlpv@ise.fraunhofer.de

modules@callab.deInitial inspection

Testing a vehicle-of a PV module.

integrated
PV module.

49

Strategy and Business Areas

Optical and Thermal Characterizationof Building Façades

Testing of Collectors, Storage Tanks and Systems

In TestLab Solar Façades, we characterize transparent, trans­
lucent and opaque materials. We also test and evaluate theenergy-relevant, thermal and optical properties of façade
components and systems. The Lab encompasses both indoor
laboratories with controlled boundary conditions, as well as an
outdoor facility “CONTINENT” to test the thermal and day­lighting performance of complete façade systems under real
boundary conditions.
TestLab Solar Façades is accredited for determining transmit­
tance, reflectance, g value and U value by measurement andcalculation. Our speciality is testing objects which often cannot
be characterized adequately by conventional testing methods,
such as building components with angle­dependent andpolarization­dependent properties, light­scattering materials or
structured and light­redirecting elements.

The portfolio of the accredited TestLab Solar Thermal Systems
covers testing as the basis for market authorization and certi­
fication of solar thermal collectors and thermal storage units,
as well as complete systems and their components for heating,ventilation and air conditioning. For solar air­heating collectors,
we are the only test laboratory in the world that is accredited
to conduct complete testing according to ISO 9806:2017.
Cooperation with the accredited TestLab PV Modules allows us
also to offer measurements for complete certification of PVT
collectors. To test hybrid heating systems, we work together
with the accredited TestLab Heat Pumps and Chillers.

Our indoor solar simulator achieves high reproducibility, whichis especially important in the context of product develop­
ment. Our outdoor test stands are designed for testing bothlarge­area collectors and concentrating collectors. In addition
to many tests specified in standards, we also individually test
the mechanical stability of mounting systems, PV modules andWe have extensive research experience in solar­control systems, solar­thermal collectors in the temperature range from ­40 °C
building­integrated photovoltaics (BIPV) and building­integrated to +60 °C, as required by our clients. With in situ character­solar thermal technology (BIST). BSDF data sets (bi­directional
ization, we can also measure systems for our clients in the
scattering distribution function) are determined goniometrically field. We carry out factory inspections for our clients aroundand are used in simulation programs to evaluate daylight use
the world, also applying remote procedures, within the Solarand glare.
Keymark certification programme.
In addition, TestLab Solar Façades is recognized as a notified
Stefan Mehnert
body and is thus authorized to test building products withregard to energy economy. It is the European Regional Data
Aggregator (RDA) for the National Fenestration Rating Council(NFRC) and advises European glazing manufacturers who intend
to address the North American market with their products.
Johannes Hanek

Phone +49 761 4588­5741

Phone +49 761 4588­5673

testlab-solarfacades@ise.fraunhofer.de

Strategie und Geschäftsbereiche

testlab-sts@ise.fraunhofer.de

IlluminatedSolar collectors

sample at theon the outdoor

aperture oftest stand.

an integrating
sphere.

Accredited Laboratories

TestLabHeat Pumps
and Chillers

Measurement and Testing of Heat Pumps
and Chillers
In the TestLab Heat Pumps and Chillers, we develop, measure
and characterize heat pumps and chillers, as well as their com­ponents. The modular test rig concept makes it feasible to test
different types of technology and system configurations underoperating conditions with different heat transfer media (air,water, brine). In addition to electrically driven systems, thermal­
ly driven equipment (with heat, natural gas or test gas) can
also be measured. The laboratory is equipped with an integrat­
ed safety concept which allows components and systems withflammable refrigerants or ammonia to be measured.
Test objects with heating or cooling power of up to 100 kW
can be measured in a calorimetric double climatic chamberat temperatures between ­25 °C and +50 °C and relative air
humidity values between 25 % and 95 %. The laboratory has
several conditioning units for water or brine, which can provide
the relevant medium at temperatures from ­25 °C to +95 °C ina thermal power range up to 75 kW. In the three air­handlingunits, the air current (80 m3/h to 5000 m3/h) can be con­ditioned in the temperature range from ­15 °C to +50 °C
and relative air humidity from 15 % to 95 %.

Characterization of Power Electronics Equipment
The accredited TestLab Power Electronics offers testing of elec­
tric units and systems in the power range up to approximately
10 megawatts. It can draw on the extensive equipment of theCenter for Power Electronics and Sustainable Grids and profits
from its own connection to the 110 kV grid.
The laboratory equipment enables us to test the electric prop­
erties of inverter systems, characterize them according to cur­rent grid connection guidelines and carry out climatic­chamber
tests to clients’ specifications. We mainly test PV and battery
inverters, but also internal combustion engines for combined
heat and power (CHP) plants or loads such as rapid charging
stations for electromobility. The laboratory is equipped withdifferent transformers, test rigs to simulate grid faults (up to
10 MVA), grid simulators (up to 1 MVA), DC sources (each
1 MW), protection testing devices and an RLC load for antiislanding tests (400 kVA).
Furthermore, we offer our clients field measurements, forinstance of large PV or wind power plants. For this purpose,
we have six power measurement systems, each with 16
measurement channels, which can be spatially distributedand synchronized as required in the field.

In our laboratory, which is accredited according to
ISO / IEC 17025, we test systems according to all common
standards and technical codes. Beyond standardized methods,
we cooperate with our clients to develop individual, realistic
measurement procedures.

We measure power­generating units according to international
grid feed­in codes (e.g., for Germany, China or Great Britain)
and determine the efficiency of power electronic equipmentwith high accuracy.

Ivan Malenković

Steffen Eyhorn

Phone +49 761 4588-5533
Mobil +49 162 205 3924

testlab-hpc@ise.fraunhofer.de

Phone +49 761 4588­5957

testlab-pe@ise.fraunhofer.de

Measurement of

1 MW batterya heat pump.

simulator in
TestLab PowerElectronics.

51

Highlights of our Research		

52

Highlights of our Research“With our industriallyrelevant research anddevelopment, we
aim to support rapid
implementation of theenergy transition.”
Prof. Hans-Martin Henning, Prof. Andreas Bett
Institute Directors Fraunhofer ISE

53

Highlights of our ResearchContents

Highly Efficient and Scalable Perovskite-Silicon Tandem Solar Cells ������������������������������������������� 56
Progress in the Development of Organic Solar Cells with High Visible Transmittance����������������� 57
Development of Highest-Efficiency Micro-CPV Modules ����������������������������������������������������������� 58“III-V on PorGe”: Inexpensive III-V Multi-Junction Solar Cells
Based on Porosified Germanium����������������������������������������������������������������������������������������������� 59
TOPCoRE Solar Cells on Gallium-Doped Cz-Si Wafers (p-type)��������������������������������������������������� 60
Contact-Free Inline Measurement of Solar Cell IV
Characteristics Assisted by Artificial Intelligence������������������������������������������������������������������������ 61
Saving Silver – a Scarce Raw Material: Copper Electrodes for
Sustainable TOPCon Solar Cells������������������������������������������������������������������������������������������������� 62
Calibration and Electrical Characterization of
Perovskite-Silicon Tandem Solar Cells and Modules������������������������������������������������������������������� 63
PV Canopies for Roads – an Important Building Block for the Energy Transition������������������������ 64
Climate-Resilient Floating Power Plants������������������������������������������������������������������������������������� 65
Probabilistic Forecast of Solar Irradiance Based on Satellite Data ��������������������������������������������� 66
Digitalization of Research Data Illustrated by Innovative Battery Technologies as an Example����� 67
First Medium-Voltage String Inverter in the World for Future Large-Scale PV Power Plants��������� 68
Electromagnetic Transient Modelling (EMT) of Inverters Applying Standardized Interfaces ������� 69
Effects of Distributed Electricity Storage Systems on the Low-Voltage Grid ������������������������������� 70
New Processes to Extract Raw Materials from Geothermal Brines ��������������������������������������������� 71

54

Highlights of our Research

Topics which specifically affect our work in
the context of sustainability are identified
with this symbol.

Digital Method to Completely Represent the Automation of Building Services���������������� 72
Extending the Application Range for Thermally Driven Adsorption Chillers���������������������� 73
Developing Heat Pumps with Propane for the Market ���������������������������������������������������� 74
Efficient Decarbonization of Heating and Cooling by Innovative Thermal Storage������������ 75
Field Measurements to Evaluate the Efficiency and Acoustic Emissions ofHeat Pumps in Existing Single-Family Houses������������������������������������������������������������������ 76
Photovoltaic-Thermal Collectors – New Product Solutions for a Growing Market ������������ 77
Standardized BIPV Façade Elements with Integrated Power Electronics���������������������������� 78
Corrosion Barrier Layers for Bipolar Plates andPorous Transport Layers in PEM Electrolysers ������������������������������������������������������������������ 79
A National Hydrogen Strategy for the United Arab Emirates�������������������������������������������� 80
Along-the-Channel PEM Electrolysis Cell for Spatially
Resolved Investigation of Mass Transport Effects������������������������������������������������������������ 81
Dimethyl Ether as a Global Hydrogen Carrier������������������������������������������������������������������ 82
Performance and Lifetime of Fuel Cells after Use of Contaminated Hydrogen������������������ 83
Transformation Paths toward Decarbonizationof the Heating Sector: a Bottom-up Approach���������������������������������������������������������������� 84
Joint Building Electricity Supplies: Comparisonof the Economic Viability of On-Site Systems ������������������������������������������������������������������ 85
Decarbonization of the Energy Supply for Real Estate Property���������������������������������������� 86

55

Highlights of our Research: Photovoltaics – Materials, Cells and Modules

Highly Efficient and Scalable
Perovskite-Silicon Tandem Solar Cells
Perovskite-silicon tandem solar cells have become promisingtechnological successors to silicon solar cells. They extend thevery mature silicon solar cell technology, as a perovskite with alarge band gap is deposited on top of a silicon solar cell, so that
better use can be made of the energy of the solar spectrum. On
a laboratory scale, this type of perovskite-silicon solar cells has
already achieved efficiencies exceeding 33 %. To produce such
efficient solar cells, all of the cell layers must be finely tuned tomatch each other exactly and the interfaces must be optimized.
We are tackling this task together with five other Fraunhofer
Institutes in the Lighthouse Project, “MaNiTU“.

Cross-section of aperovskite-silicontandem solar cellunder the electron
microscope.

c-Si
c-Si

As not all of the previously applied laboratory production me­
thods are suitable for industrial manufacturing, we are working
intensively at Fraunhofer ISE on the development and evaluationof production methods that can be used for mass production.
In the “PrEsto“ project, the focus is on the so-called hybrid pro­cess, in which the perovskite absorbers are produced in a twostage process. We have already achieved efficiencies of 30 %with this method. The advantages of this method are that the
textured silicon solar cells that are usually used in the industry
can be coated conformally and that scalable process technology
is available. On this basis, we were able to produce a tandem
solar cell in M2 format.

Contact

Perovskite-silicontandem solar cellin M2 format.

Dr. Juliane Borchert
Phone +49 761 203-5475
juliane.borchert@ise.fraunhofer.de

56.

Based on this experience, we have now begun to establish
an independent technological platform within the “PeroSi-SCALE“ and “LiverPool“ projects, enabling the further
development and analysis of cell and module designs as wellas their production processes for perovskite-silicon tandem
solar cells.
Due to the enormous variety within the perovskite group ofmaterials and the associated opportunity to define the absorp­
tion properties over a wide spectral range, it is also possible tocombine several different perovskite solar cells with a siliconsolar cell and thus achieve still higher efficiencies than with
only two materials. Triple-junction solar cells, which consist of
one silicon sub-cell and two different perovskite sub-cells, arethe subject of research in the EU-funded “Triumph“ project
and the “RIESEN“ project. The high voltages and low currentsof such solar cells reduce the power losses due to cell metal­
lization and connection, and thus also reduce the material
consumption of valuable silver or copper. At Fraunhofer ISE,
we have now achieved an extremely high open-circuit voltage
exceeding 2.8 V for this type of solar cell. This is an important
step for the development of this new triple-junction solar cell.

The Pero-Si-SCALE, LiverPool and RIESEN projects are fundedby the German Federal Ministry for Economic Affairs andClimate Action (BMWK).

Highlights of our Research: Photovoltaics – Materials, Cells and Modules

Progress in the Development of Organic Solar Cells
with High Visible TransmittanceIn the “See-Through-PV“ project, we are developing organic
solar cells with high visible transmittance, in cooperation
with our partners from the industry and the University ofFreiburg. In doing so, we use the unique optical properties ofcertain organic semiconductors which are transparent to lightin the visible spectral range and simultaneously exhibit strong
absorption in the near-infrared (NIR) range. This enables the
production of semi-transparent solar cells which are homoge­
neous over their whole area. To increase their efficiency, theapplication of special electrode systems is needed.
Whereas the front electrode should be as transparent as
possible over the entire solar spectral range, the back electrodeshould combine high visible transmittance with high NIR reflec­
tance. To this purpose, we use an electrode system developed
at Fraunhofer ISE, based on thin silver films, which possesses
the desired optical properties and simultaneously features suf­
ficiently high electrical conductivity. Concretely, we have useda layer stack of AZO/Ag/AZO/Ag/AZO, whereby AZO stands for
Al-doped zinc oxide. The individual coatings are deposited by
sputtering.
The photo-active organic material was applied from non-chlo­
rinated solvents, as would be required in industrial production.
A transparent, conductive polymer (PEDOT:PSS) is used as theupper electrode and is produced by our cooperation partner,
Heraeus. By applying a new PEDOT:PSS formulation and adjust­ing the film thickness of the absorber, high visible transmittan­
ce was achieved. In addition, we succeeded in increasing thenumber of NIR photons that are reflected back into the active
layer, by optimizing the back electrode. This increases theamount of current generated by the solar cell without
decreasing transmission in the visible range.
As a result of these developments, we fabricated organic
solar cells with an efficiency of 8.7 % and an average visible
transmittance (AVT) of 46.3 %. The so-called light utilization
efficiency (LUE) is often used to compare semi-transparent
solar cells with different transmittance values with each other,quickly and simply. It is the product of the efficiency and the
AVT. Our organic solar cells reach an LUE of 4.0 %. This is avery promising value, as the cells do not contain indium tinoxide and are processed using non-chlorinated solvents.
Due to the manifold possibilities of synthetic organic chemistry,it can be assumed that new, improved semiconductor mate­rials will be found which enable further increases in efficiency.
This opens up new application areas for organic photovoltaics,
particularly in the fields of building-integrated photovoltaics
and agri-photovoltaics. Thanks to their low weight, the easeof integration and their advantageous appearance, organic PV
has the perspective of making a valuable contribution toward
increasing public acceptance of integrated photovoltaics.

The See-Through-PV project is funded by the German Federal
Ministry for Economic Affairs and Climate Action (BMWK).

Contact
Organic solar cellwith high visible
transmittance.

Dr. Uli Würfel
Phone +49 761 203-4796
uli.wuerfel@ise.fraunhofer.de57

Highlights of our Research: Photovoltaics – Materials, Cells and Modules

Development of Highest-Efficiency
Micro-CPV Modules
Concentrating photovoltaics uses lenses to concentrate direct
solar radiation by factors of a hundred to a thousand anddirect it onto extremely high-efficiency III-V multiple-junction
solar cells. In our most recent module development at
Fraunhofer ISE, which we call micro-CPV, we are using par­ticularly small solar cells with an edge length of 0.585 mm.
Although each cell generates only a small amount of power
due to the small solar cell and lens areas, this feature meansthat we can use thin copper circuits to connect the solar cells
electrically to each other and to remove heat. This saves
material for additional cooling elements.

Micro-CPV module developed at Fraunhofer ISE, with a module
efficiency of 36.5 %, the highest efficiency for a module withindustrial components from Europe.

At Fraunhofer ISE we are developing the most modern, highthroughput processes for the construction and connection tech­
nology, which make it possible to position many components
simultaneously and very rapidly on the base plates of the mod­ules. At the same time, the tiny solar cells must be positioned
exactly in the focus of the lenses. However, the surface tensionof the molten solder under the solar cells helps us to align thecomponents on the printed circuit. This phenomenon is called“self-alignment”. This effect means that the required tolerancesin the module can be met, even with a positioning accuracy ofthe solar cells in the range of 150 µm.
In 2022, we were able to measure the first modules of the newgeneration on our outdoor test stand within the “micro-CPV“
project: Under concentrator standard test conditions (CSTC),
we achieve an excellent efficiency here of up to 36.5 %. We
used III-V solar cells, consisting of five sub-cells stacked on topof each other, from the AZUR Space company in Heilbronn.
The III-V multi-junction solar cells were originally developed forsatellites and then adapted to the conditions in concentrator
modules.

Micro-CPV cells are positioned on the printed circuit board
forming the module base. The solar cells can be accurately
positioned due to self-alignment of the solar cell chips.

Contact

The micro-CPV project
was funded by theGerman Federal Ministry

Dr. Frank Dimrothfor Economic Affairs andPhone +49 761 4588-5258

Climate Action (BMWK).

frank.dimroth@ise.fraunhofer.de

58

The micro-CPV modules must track the sun very accurately, sothey are particularly well suited for the solar belt of the earth.
Here, we also foresee good synergy with the production ofsolar hydrogen. Furthermore, the high efficiencies and small
solar cell areas of concentrating photovoltaics allow valuable
resources and energy to be saved in their production. As the
supply industry is located completely within Europe, concentrat­
ing photovoltaics guarantees a high degree of tech­nologicalsovereignty and independence with regard to raw materials.
Within the Fraunhofer Deeptech Accelerator AHEAD, we are
currently evaluating the establishment of a new spin-off
company for commercial further development of thetechnology.

Highlights of our Research: Photovoltaics – Materials, Cells and Modules“III-V on PorGe”: Inexpensive III-V Multi-Junction
Solar Cells Based on Porosified Germanium
Compared to single-junction solar cells, III-V tandem solar cells
feature higher efficiencies in converting sunlight to electricity.
Their main components are different photo-active absorberlayers. However, these are produced applying a relatively slow
process, namely metal-organic vapor phase epitaxy (MOVPE),
and expensive gallium arsenide (GaAs) or germanium sub­strates. In addition, the solar-cell processing is complex andhas a low throughput. The substrate, epitaxial layer growthand processing each represent about a third of the total costs.
Thus, each of these steps along the route to the final solar cellmust become more cost-efficient. At Fraunhofer ISE, we havedeveloped approaches which can lead to cost reductions.
The germanium substrate is initially used in a thickness which
is not needed for the final solar cell but is required to with­stand the mechanical loads during processing. To significantly
reduce the consumption of substrate material, we make useof electrochemical porosification followed by a high-tem­
perature annealing process. During porosification, material isdeliberately removed such that a porosity gradient is created.
A controlled-fracture plane in the substrate is created by theannealing process. The final substrate thickness is reduced toapp. 0.8 – 0.9 µm. The III-V cells are then grown on the modi­
fied substrate. After the solar-cell processing, the solar cell isseparated along the controlled-fracture plane (see illustration).
The initial substrate is then available to be re-used in the
production cycle.

The relatively high costs of III-V epitaxy result primarily fromthe long processing times. Typical growth rates, e.g. for GaAs,
are lower than 10 µm/h, for absorber thicknesses of up to
3 µm/h. We were able to demonstrate that growth rates
exceeding 280 µm/h are possible with MOVPE after cleverprocess optimization. In addition, it became evident that V:III
ratios (ratio of group V precursors to group III) that are fivetimes smaller are advantageous at growth rates > 100 µm/h
and that the incorporation efficiency of the group III precursors
can be increased by 60 %. For a growth rate of 100 µm/h,
already an efficiency of 23.6 % has been demonstrated for the
first single-junction GaAs solar cells. We are developing thisapproach further in the “H2DEMO“ and “Vorfahrt“ projects
and transferring it to tandem cells.
Also, the costs for metallization (cell processing) can be clearly
reduced by the mask-and-plate approach, as we were able todemonstrate in the “SALLI“ project. Here, the mask is applied
by material-saving inkjet printing and the metal is depositedby plating through narrow openings. Finger widths of only 10µm have already been demonstrated with this approach. The
first resulting triple-junction solar cells achieved efficiencies
exceeding 30 %.
All of these developments that we have researched at
Fraunhofer ISE, the re-use of the germanium substrates
and the higher throughput rates for III-V film growth andsolar cell metallization, lead to significant cost reductions
for III-V tandem solar cells.

SEM image (left) of the schematic thin-film stack (center)

The H2DEMO project was funded by the German Federal

after porosification, annealing and III-V epitaxy. Photo of

Ministry for Education and Research (BMBF). The SALLI projecta high-efficiency III-V / Si tandem solar cell with mask-and-

was funded by the German Federal Ministry for Economic

plate front metallization (right).

Affairs and Climate Action (BMWK).

Contact

Dr. Waldemar Schreiber
Phone +49 761 4588-5641
waldemar.schreiber@ise.fraunhofer.de59

Highlights of our Research: Photovoltaics – Production Technology and Transfer

TOPCoRE Solar Cells on Gallium-Doped
Cz-Si Wafers (p-type)
In industrial solar cell production, a clear trend away fromPERC solar cells on p-type wafers toward solar cells basedon n-type wafers with charge-carrier-selective contacts cancurrently be identified. At present, TOPCon solar cells repre­
sent the largest share – technology, which was developed at
Fraunhofer ISE. The industry’s current choice of n-type Cz-Si is
influenced by the higher wafer costs compared to p-type Cz-Si
wafers.
At Fraunhofer ISE, our record efficiencies for laboratory TOP­
CoRE solar cells on p-type FZ-Si wafers and simulations were
early demonstrations that these have a higher efficiency poten­
tial than TOPCon solar cells of n-type silicon. During solar cell
production on p-type wafers, a phenomenon occurred which
we called light-induced improvement (LII) and have investigat­
ed in greater detail. In LII, solar cell parameters improve underillumination within seconds, which presents challenges to theclassification of solar cells for module construction. To facilitate
a possible technological transfer to industry, our goal was to
identify the cause of the rapid improvement. To this purpose,
we prepared test structures which represent the different
regions of a TOPCoRE solar cell: A) back surface (tunnel oxide+ poly-Si(n++) + SiNx:H), B) front surface of the TOPCoRE solarcell, C) TOPCoRE solar cells, D) I-Voc test architectures. The testarchitecture which represents the back surface (A), did notshow any rapid improvement under illumination, althoughextraordinarily long charge-carrier lifetimes and implicitly highopen-circuit voltages were measured. This implies that neither
the back-surface passivation nor the gallium-doped p-type
wafers were the cause for the rapid light-induced improve­ment. However, all other architectures (B, C and D) displayed
LII.
LII can already be observed before metallization or the firing
process for metal contacts. In addition, we demonstrated
on the symmetric test architectures which represented the
TOPCoRe front surface that LII occurs, regardless of whether
high-temperature processes like boron diffusion and poly-Si
annealing are applied or not. It is known from literature that
AlOx, which is used to passivate the front surface, can lead to
LII – but the reported periods of time were many times longer.
It is also known that e.g. the bonds between the atoms of
Fe-Ga or Fe-B pairs break under illumination, resulting in theformation of interstitial Fei.
As TOPCoRE solar cells on p-type silicon can contribute to
reduced production costs for solar energy, we will continue
to conduct further research at Fraunhofer ISE to identify thecause for LII. In doing so, we aim to pave the way for the PV
industry to adopt this solar cell structure.

Structure and initial cell results for
TOPCoRE laboratory proto­t ype
solar cells with local p-TOPCon
front contact passivation.

Contact

Dr. Jochen Rentsch
Phone +49 761 4588-5199
jochen.rentsch@ise.fraunhofer.defront contact passivation

Jsc [mA/cm2]

Voc [mV]

FF [%]

η [%]local TOPCon

41.7

728

81.1

24.6

Internal measurement, 4 cm2 designated area, without a double-layer MgF2 anti-reflective
coating (ARC).

60

Highlights of our Research: Photovoltaics – Production Technology and Transfer

Contact-Free Inline Measurement of Solar Cell IV
Characteristics Assisted by Artificial Intelligence
One option to reduce the production costs of solar cells is
to increase the throughput of all production facilities. In the“NextTec“ project, we have thus investigated the potential
to accelerate the production process. Measurement of thecurrent-voltage (IV) characteristic at the end of the production
line is mandatory but reduces the throughput considerably, as
the cells must be contacted for the measurement, which takes
more time than the measurement itself. In the previous Annual
Report of Fraunhofer ISE for 2022/23, we already presented aphysical model for contact-free IV mea­sure­ment of solar cells.
An alternative contact-free approach, which is based on artifi­
cial intelligence and extends image analysis, requires less and,above all, only rapid inline-compatible measurement techno­
logy, such that a throughput of up to 20,000 cells/hour is pos­sible – and thus an increase in throughput by about a factor
of four. Our process is based on a series of photolumi­nescencemeasurements under varying illumination intensity and shad­ing(see illustration) and a spectral reflectance mea­surement.
Each measurements provides information on different quality
properties of the cell, although relevant characteristic datacannot be derived simply from individual measurements. A
convolutional neural network was thus developed to com­bine all of the spatially and spectrally resolved data from thecontact-free measurements and determine the relevant quality
characteristics of the solar cell, such as efficiency, open-circuit
voltage or also the complete IV characteristic of the cell, fromthe patterns found in the multi-dimensional data. In an ex­­tensive study, a data set was created with 4500 samples totrain and evaluate the models. Analysis of the models demon­
strated that very good agreement exists between the contactfree, AI-based predictions and the results from measurement
instruments on contacted cells (see graph). Furthermore, we
showed that cell sorting based on contact-free measurements
resulted in the same module quality as with contact-based
measurements.
Compared to contact-based measurements, the contact-free
IV measurement has numerous advantages with respect tothroughput, maintenance costs and down times. Elimination of
the contacting step means that the measurement time can be
reduced. In addition, the mechanical pressure exerted by thecontact bars on the cell is avoided, reducing the breakage rate
and thus the down time of the production line. In addition,
costs due to wear and maintenance are avoided by dispensing
with contact bars.

Partly shaded (upper row) and homogeneously
illuminated (lower row) photoluminescencemeasurements of an example cell.

Comparison ofefficiency µ as
determined bycontact-basedand contact-freemeasurements.

21.0 21.3 21.6 21.9 22.2
Contact-based η (%)

The NextTec project was
funded by the German
Federal Ministry for Eco-

Contact

nomic Affairs and Climate
Action (BMWK).

Dr. Stefan Rein
Phone +49 761 4588-5271
stefan.rein@ise.fraunhofer.de61

Highlights of our Research: Photovoltaics – Production Technology and Transfer

Saving Silver – a Scarce Raw Material: Copper
Electrodes for Sustainable TOPCon Solar Cells

TOPCon solar cell metallized with purely
copper-based paste (test layout).

The increasing share of photovoltaics in the global energy mix
demands higher efficiencies and sustainable production pro­
cesses. To conserve valuable resources, we at Fraunhofer ISE
have investigated path-breaking approaches for more sustai­
nable metallization processes for solar cells. High-efficiency
solar cell concepts, such as the TOPCon technology developed
at Fraunhofer ISE, are currently increasing their market share.
However, they still have the disadvantage that they need signif­
icantly more silver than previous concepts. As a consequence,a scarcity of silver could lead in future to clear price increases
and even jeopardize the total global production volumes.
Up to now, work has concentrated primarily on producing
increasingly fine “fingers” with the established screen-

Contact

In 2023, a new prototype
facility for research on cell
metallization by nickel-

Dr. Sven Kluska

copper-silver electro-plating

Phone +49 761 4588-5382

was commissioned atsven.kluska@ise.fraunhofer.deFraunhofer ISE.

62

printing processes, so that the amount of silver used could be
reduced (fine-line screen printing). In this R&D area, haverepeatedly achieved new record values, which were sub­sequently reflected in industrial production. An alternative tosilver is copper – it is appreciably less expensive and has a com­parable conductivity. If some of the silver in the printing pastes
is replaced by copper, much of the previous production tech­
nology can remain unchanged. Because copper oxidizes very
quickly and is thus more difficult to handle, we initially concen­
trated on silver-coated copper particles. In the mean­time, goodresults can also be achieved with silver/copper blends or purely
copper-based pastes. In the first experiments, we initially tested
a printed copper metallization for the back of TOPCon solar
cells. These tests proved that the same performance could beachieved as long as an ex­temely small amount of screen-printed
silver was used for the contact layer. This approach saves up to
45 % silver per cell and can be adopted in industrial productionin the near future.
Electro-plating with metals is an alternative approach fromwhich silver can be almost completely eliminated. A metal
contact is created by laser ablation and electro-plating of nickel,
copper and silver. We have tested electro-plated nickel-cop­per-silver contacts on industrial TOPCon solar cells, thereby
demonstrating a 90 % reduction in silver consumption andefficiencies exceeding 24 %. The cells have already been further
processed with soldered contacts to form 60-cell modules.
Based on these successes, we commissioned high-throughput
pilot electro-plating equipment at Fraunhofer ISE within the“Indianapolis” project. The goal now is to develop these results
further in close cooperation with industrial partners so that thesustainable TOPCon metallization with copper electrodes canbecome established.

Highlights of our Research: Photovoltaics – Production Technology and Transfer

Calibration and Electrical Characterization of
Perovskite-Silicon Tandem Solar Cells and Modules

1 µm

Wavelength l (nm)Measurement of the spectral irradiance of color channel #11(385 – 760 nm) for different intensities. To characterize thespectral properties of different LEDs under real operating
conditions, these are not characterized separately, as is theusual approach, but within a composite base spectrum with
contributions from all LEDs.

The new solar simulator
marks a milestone toward
establishment of a stan-

Contact

dardized procedure forcalibrating perovskitesilicon tandem modules.

Alexandra Schmid
Phone +49 761 4588-5066
alexandra.schmid@ise.fraunhofer.de63

Highlights of our Research: Solar Power Plants and Integrated Photovoltaics

PV Canopies for Roads – an Important
Building Block for the Energy Transition
as ensuring water run-off. As the glass-glass PV modules areauthorized for overhead glazing, it was possible to integratethese into the construction without additional safety measures.
The transparent gaps between the solar cells transmit lightonto the road surface. Altogether 96 PV modules with a total
power of 30 kWp have been installed.

Demonstration of a PV canopy for roads at the Hegau-Ost
rest area, Baden-Württemberg, Germany.

Photovoltaic installations over motorways can make a signi­
ficant contribution toward climate neutrality with theirsolar-generated electricity. Within the “PV-Süd“ project, we
at Fraunhofer ISE have cooperated with the Austrian Instituteof Technology AIT and the company, Forster Industrietechnik
GmbH, to develop, plan and implement a demonstration PV
canopy for roads.
The pilot installation is located over the transit lane of the
Hegau-Ost rest area on the German A81 motorway. In prepa­
ration, the project consortium had developed and tested thesuitability of and the requirements on the PV modules and thesub-structure for the road canopy in laboratory experiments
and by simulation. In doing so, the high demands of the trans­
port sector were taken into account, e.g. protection against
impact and fire. The 12 m x 14 m area of the PV module
canopy, which is located about 5.5 m above the road level, ismounted on a steel structure. The PV modules are configured
to form a shed roof to guarantee a high electricity yield as well

Contact

Detail of the translucent modules of thedemonstration PV

Jacob Forster

canopy at the Hegau-

Phone +49 761 4588-2282

Ost rest area, Baden-jacob.forster@ise.fraunhofer.de

Württemberg, Germany.

64

Within the PV-Süd project, we will investigate the yields, theeconomic viability and the potential advantages of road cano­pies. Applying the assumed costs and scaling effects for the
PV generator, specific system costs of less than 5000 €/kWp
are possible. The sub-structure plays a decisive role, as this hasless potential for the scaling effects of industrial production.
On the basis of the potential power of 30,000 kWh/year fed
into the grid by the demonstration canopy, which was calcu­
lated during the concept phase, the economic viability can be
determined as a function of the feed-in tariff. Due to the highcosts of the sub-structure, PV road canopies cannot compete
economically with conventional ground-mounted installations.
Nevertheless, they make use of already sealed areas of trans­
port infrastructure and could amortize themselves over the
lifetime of the sub-structure by “re-powering” with several
generations of PV modules, which has a positive effect on theirecological footprint. This is particularly relevant for lower-pri­ority road traffic, e.g., within built-up areas or over cycleways,
as there the sub-structure can be reduced in comparison tolocations near motorways.
PV road canopies for high-priority roads (particularly motor­ways) are an option that is fundamentally interesting where
the electricity can be used directly, e.g. near tunnels or rest
areas, as the load profile for a tunnel matches the generation
profile of PV modules well. The partial transparency of the
canopies also helps with visual adaptation by vehicle drivers
to the darkness in the tunnel.

Highlights of our Research: Solar Power Plants and Integrated Photovoltaics

Climate-Resilient Floating Power Plants

Floating PV (FPV) is a relatively new technology in Europe –with appreciable potential at a global level. Floating PV power
plants consist of PV modules which are located on floating
sub-structures on water. It must be assumed that FPV systems
affect the hydrology and the ecosystem of the water bodies
but the concrete effects of floating PV have not yet been ade­quately researched. In particular, the influence of FPV on the
climatic resilience of the water body is still unclear. This resi­l­ience is endangered as a result of climatic change: The thermal
properties of lakes will change in the foreseeable future, which
can negatively affect the mixing of different water layers
and their ecological quality. It is also to be expected that theclimatic changes will compromise the function of lakes as sinks
for carbon. Thus, we at Fraunhofer ISE have investigated theeffects of FPV on thermal behavior, water quality and evapora­tion in various studies.
The Maiwald Lake is one of numerous former gravel pits in theUpper Rhine Valley. In a field study, the local FPV system andits surroundings were monitored to document changes in thethermal properties of the lake. Effects were observed particu­
larly in the upper water layers – down to a layer thickness offive meters. Thus, the water underneath the system was up
to 2.8 K cooler during the day of hot periods, whereas it was
up to 1.4 K warmer during the night due to reduced thermal
emission. When systems covering different proportions of
the water area were modeled, it became evident that larger
systems would result in less stable thermal stratification andshorter stratification duration in the lake. Thus, these systems
would act to mitigate the anticipated effects of climaticchange.

The “FPV4Resilience” project investigates the extent to which
FPV can increase the climatic resilience of lakes. An extensive
monitoring scheme was established at the locations of various
European FPV power plants, which differ with respect to
the FPV system design and the type of lake. Only preferred
locations for the installation of floating PV, such as gravel pits,
sand pits or dams, were taken into account. The project goal
is to derive a definition of the climatic resilience of lakes fromthe interaction of floating PV with the lake and hydrologicaland meteorological characteristics. Finally, simulation will beapplied to determine the Pareto optima of electricity yield andclimatic resilience, and compared to the available measurement
data.
Lake Nasser is one of the largest artificial lakes in the world
and is traversed by the border between Egypt and Sudan. It is
to be assumed that floating PV offers great potential to reduce
evaporation in arid regions with large water reservoirs. Thus,
we carried out a modeling experiment in which different areasof FPV systems on the reservoir were simulated and the asso­
ciated water savings were calculated.
Depending on the system size, these water savings amounted
to 600 – 5900 million m³/a (7.67 m3/(a * kWp) on average). In
addition, an optimized water management program for agri­
cultural irrigation was derived from the simulation of different
scenarios. Electricity yield simulations revealed that covering
45 % of the lake with floating PV would – on average – meetthe current electricity demand of Africa.

The FPV4Resilience project was funded by the Sustainability
Center Freiburg.

Floating PV system on a

Contact

former gravel pit near
Leimersheim, RheinlandPfalz, Germany.

Konstantin Ilgen
Phone +49 761 5488-5707
konstantin.ilgen@ise.fraunhofer.de65Highlights of our Research: Solar Power Plants and Integrated Photovoltaics

Probabilistic Forecast of Solar Irradiance
Based on Satellite Data
Electricity generation from the sun and the wind depends on
the weather – this influences the electricity supply and its dis­tribution. Meteorological forecasts are helpful in improving the
integration of electricity from renewable sources into electri­
city grids. However, the forecasts are always subject to someuncertainty. Probabilistic forecasts provide probability distribu­
tions instead of a single predicted value (point forecast). Using
these distributions, uncertainties can be predicted, minimizing
risks and costs.

Clouds over the French island of La Réunion, locatedin the Indian Ocean; photographed from the ISS spacestation.

In the “SOLREV“ project, we are develop­ing probabilistic fore­casts of solar irradiance on the basis of established point fore­
cast procedures. As part of the project, we are participating as
the German partner in PVPS Task 16, “Solar Resource for High
Penetration and Large Scale Applications” of the International
Energy Agency (IEA), contributing to the topic of solar energy
meteorology. Within the Task, we participated in an interna­
tional benchmarking exercise on probabilistic forecasts, which
was conducted in 2022 under the direction of the Universitéde La Réunion.
The uncertainty of solar irradiance forecasts depends on theweather conditions, particularly the variability of the cloud
cover. Situations with a clear sky or a completely overcast sky
lead to low uncertainty, whereas intermittent cloud cover
results in large uncertainties (see graph). To reflect these differ­
ent uncertainties, we search for similar situations in the paston the basis of historical point forecasts and derive the soughtprobability distributions from the corresponding measured
values.

Probabilistic forecasts (gray regions) of the global
horizontal irradiance (GHI) from 9 th to 11th May, 2018
in Payerne, Switzerland.

Contact

Tobias Zech

We calculate our point forecasts from three data sources bycombining current measured values, satellite-based forecasts
and numerical weather predictions (NWP) with machine-basedlearning methods. The satellite-based predictions are better
than those based on measured values after about 30 minutes
and are better than NWP-based procedures up to about twohours. In this way, the forecast horizon from 15 minutes tosix hours is optimally covered. Whereas measured values and
NWP are already established as bases for probabilistic predic­tion, the use of satellite-based forecasts is new in this context
and led in the benchmarking exercise to a significant improve­
ment in the probabilistic forecast quality.

Phone +49 761 4588-5036
tobias.zech@ise.fraunhofer.de

The SOLREV project was funded by the German Federal Ministry
for Economic Affairs and Climate Action (BMWK).

66

Highlights of our Research: Electrical Energy Storage

Digitalization of Research Data Illustrated by
Innovative Battery Technologies as an Example
The digital transformation in research opens up numerous pos­sibilities to develop innovative, data-based services and new,digital business models. For the Fraunhofer-Gesellschaft, thischange presents a challenge and an opportunity at the sametime, as digitalization requires not only the establishment ofsuitable infrastructure but also a working-culture transforma­tion to standardized data management. Consistent and logicaldigitalization of research and development activities will be
inevitable in future: on the one hand, to meet requirements ofnational and international funding agencies on data handlingand on the other, to survive in international competition. At
Fraunhofer ISE, we are working toward this goal within various
projects on battery research, including the “Samba“ and“Quaze“ projects.

develop a data space that is accessible from different Institutes
and allows standardized storage and linkage of data according
to the FAIR principle, meaning findable, accessible, interoper­
able and reusable. Establishment of a digital research data
infrastructure not only advances the strategic development ofdigital competence and improves the quality of current service
offers. It also provides the opportunity to develop completely
new, digital business models that transcend the boundaries ofindividual Institutes.
Good data management facilitates data analysis and allows
large amounts of data to be evaluated by applying artificial
intelligence, approaches which we are following together withindustrial partners in the “Samba“ and “Quaze“ joint research
projects.

Different types of research and development data are
generated in the projects. These are gathered, e.g., during
the end-of-line quality control of battery cell production or in
the battery test laboratory, where we generate extensive timeseries in long-term investigations of battery cells and modules.
In addition, we carry out short-term measurements with com­plex test facilities. At present, the resulting research data areusually acquired, analyzed and saved according to individual
procedures.
The researchers decide where and in which format the data
will be stored and analyzed. In practice, this means that raw
data are saved without the meta-data which document theexact experimental procedure, ambient conditions or the ex­­perimental set-up. At a later time, these data cannot be foundby other researchers at all, or only after considerable timeand effort, and can only be inadequately interpreted. Often,
this excludes re-use of the data. At the same time, it is often
complicated to record meta-data, as they are generally notacquired automatically. In addition, at the time of the measure­ment, it is often not foreseeable which data will be relevant
for a second evaluation. Nevertheless, good scientific practicerequires accurate documentation and traceability to allow
experiments to be reproduced and understood.

Schematic diagram of thedata space, which automatically records data

Different Institutes of the Fraunhofer-Gesellschaft are thus
working on concepts for standardized and automated data
storage. As an example, Fraunhofer ISE is involved in initial
joint conceptualization within battery research. The goal is toContact

together with meta-data,processes them and organ­izes them according to the

Dr. Moritz Kroll

FAIR principle.

Phone +49 761 4588-2554
moritz.kroll@ise.fraunhofer.de67

Highlights of our Research: Power Electronics and Grids

First Medium-Voltage String Inverter in the World
for Future Large-Scale PV Power Plants
The planned expansion of photovoltaics will demand large
quantities of raw materials, including copper and aluminumfor cables and transformers. Within the “MS-LeiKra“ project,
we at Fraunhofer ISE have developed a string inverter whichfeatures a significantly higher output voltage. This can lead tomajor savings in consumed resources, as the higher voltage
results in a lower current and thus smaller cable cross-sections.
String inverters today use output voltages (line to line) be­
tween 400 VAC and 800 VAC. In the past, the voltage of thestring inverters was repeatedly increased together with theirincreased power rating. For a given power value, a higher
voltage results in a lower current and thus smaller currentdependent losses. Recently, however, there have not been any
further increases in the voltage despite continued increases in
power. This has two reasons: firstly, the challenge of construct­
ing a highly efficient and compact inverter for higher voltages
on the basis of silicon semiconductors; secondly, the currently
existing PV-specific standards apply only for the low-voltage
range. This ends at 1500 VDC or 1000 VAC.

4 mm 2@5 kV

35 mm2@1,5 kV

120 mm 2@ 0,8 kV

The potential savings which could be achieved by raising thevoltage higher are illustrated by the photo below (left). Thisis based on the assumption of a string inverter with a power

The MS-LeiKra project was funded by the German Federalcross-sections for 250 kVA for

Ministry for Economic Affairs and Climate Action (BMWK).

Medium-voltage string
inverter for future large PV
power plants. Power:
250 kVA, output voltage:
Michael Geiss

1500 VAC , PV voltage:

Phone +49 761 4588-5069

1.7 kVDC – 2.4 kVDC .

michael.geiss@ise.fraunhofer.de

68

In order to overcome the identified hurdles, we have develop­
ed the first medium-voltage string inverter in the world andsuccessfully taken it into grid-connected operation (see photo
below, right). The inverter has an output voltage of 1500 VAC
for a rated power of 250 kVA. It implements a two-stage
design. The step-up converter for a PV input voltage of 1.7 kV
to 2.4 kV is based on 3.3 kV silicon carbide (SiC) semiconduc­tors. The inverter stage was constructed with hybrid ANPC
modules (Active Neutral Point Clamped). Four silicon and two
SiC semiconductors are applied here. This topology allows
the great advantages of SiC to be used for only minimallyhigher costs. Using the demonstrator, it was shown that higher
voltages can be handled technologically and that work is now
needed to adapt the standards accordingly.

Comparison of minimum cabledifferent voltages.

Contact

rating of 250 kVA. For the output power of 800 VAC, whichis possible today, DIN VDE 0298-4, Table 9.2 demands a
minimum cable cross-section of 120 mm². If the voltage isincreased to 1500 VAC, the cable cross-section decreases to
35 mm². For an increase to 5000 VAC, only a copper cablecross-sectionof 4 mm² remains as a requirement. As cable
lengths of double-digit kilometers are installed in a large
PV power plant, enormous amounts of material can besaved by applying this measure.

Highlights of our Research: Power Electronics and Grids

Electromagnetic Transient Modelling (EMT) of
Inverters Applying Standardized Interfaces
The rapid expansion of photovoltaic and wind power plants
as well as battery storage units and electrolysers presents achallenge to stable operation of our power supply grid. In
contrast to conventional power plants, such as those basedon synchronous generators, these inverter-based systems
behave dynamically – their behavior is mainly defined bysoftware-based control algorithms. In general, this situation isadvantageous, but it requires a harmonized set of regulations
to ensure interoperability. In this context, test and validation
methods are essential to allow the compliance of system be­­havior to be checked.
Different approaches to validate the system behavior are avail­able. A trivial procedure is to measure the system in a testinglaboratory under different operating conditions. However,complete characterization can only be achieved to a limited
extent, for example, because the conditions at the system gridconnection point depend on many factors. For large powersystems, the first challenge is to find a testing laboratory witha sufficiently large capacity. Simulation-based analysis presents
an alternative. Electricity grids can be modeled holistically byusing suitable simulation environments. This is often done by
applying highly dynamic electromagnetic transient simulation(EMT), particularly in the sector of power transmission and dis­tribution operation.

Control hardware validation using

When system models are exchanged, e.g. between grid oper­
ators and system manufacturers, two essential challenges areencountered: firstly, the control algorithms, which define thesystem behavior, belong to the proprietary intellectual propertyof the given manufacturer; secondly, a form of compatibility isfavored which is independent of the simulation environment.
To overcome these challenges, Fraunhofer ISE has cooperated
with TransnetBW GmbH to develop procedures to encapsu­
late the control algorithms by compilation into dynamic link
libraries, so-called DLLs. The advantage of this procedure isthat the control algorithm is no longer in a form which canbe read or understood, such that the intellectual property ofthe manufacturer is protected. A further central aspect in thedevelopment of system models is the incorporation into any
arbitrary simulation environment. To this purpose, the suitabili­
ty of the proposed interface specification, ENTSO-E Standard­
ized control interface for HVDC SIL/HIL conformity tests, wasanalyzed for general inverter-based systems.
For the example of a three-phase 500 kVA inverter, we havedemonstrated how encapsulated DLL models can be createdand standard interfaces for highly dynamic EMT simulations
can be implemented. Investigations were conducted both ofpurely offline simulations (software in the loop; SIL), using the
PSCAD simulation environment as an example, and also of thesuitability of standard interfaces for hardware-in-the-loop (HIL)
applications. We validated the generated models and simula­tions on the basis of high-resolution laboratory measurementsof the real system.

hardware-in-the-loop (HIL) applications
and a standardized interface.

Contact

Benjamin Stickan
Phone +49 761 4588-2125
benjamin.stickan@ise.fraunhofer.de69

Highlights of our Research: Power Electronics and Grids

Effects of Distributed Electricity Storage Systems
on the Low-Voltage Grid
So-called prosumers not only consume electricity but also
produce it and participate increasingly actively in the energy
market. An example for prosumers is given by the operators of“balcony power plants” on building façades and roof-mounted
PV systems, which have recently become much more numer­
ous. Particularly in new building zones, heat pumps for spaceheating have recently been added to the electricity consump­tion side; the number of electric vehicles is also increasing
rapidly. These new electric components are increasingly being
actively controlled by energy management systems to minimize
the costs for electricity.

systems like photovoltaic systems and electric vehicles can be
operated uncontrolledly. This would only be possible if theelectricity grid were greatly extended and can be illustrated by
an example: The changes in the electricity system would meanthat 767 m of cables would have to be installed in an example
rural area with 1057 customer, corresponding to 2.5 % of theentire length of installed cables in the area. In addition, three ofthe total of 16 transformers (19 %) would need to be replaced.
These expansion requirements illustrate the enormous chal­lenges which will confront the distribution grid operators incoming years.

In an energy system that is based more and more on renew­
able energy sources, flexibility on the demand side and thus
the behavior of prosumers is becoming increasingly important.
In general, energy management systems control consumption
such that as much electricity as possible is drawn from the pro­sumer’s own photovoltaic system. Another option is to opti­
mize the use of electricity for the electric vehicle, the storage
battery and the heat pump according to the fluctuating pricesof dynamic tariffs. Increasingly, commercial enterprises are also
evolving into prosumers by orienting their consumption toward
their own photovoltaic electricity generation, to become lessdependent on the electricity market.

To aid grid integration, we propose grid-supportive behav­
ior of prosumers as a solution. This means, for example, thatprosumers charge their storage batteries when the sun isshining strongly. Or they permit the grid operator to delay the
charging of electric vehicles until the night, rather than during
the evening, immediately after many car drivers have arrived
at home. According to our calculations, these measures or
behavior changes can reduce the peak loads on the grid andgrid expansion costs would decrease by more than 30 %. In the“MAPSEN“ project, we are developing tools which will help
grid operators to quantify the behavior of prosumers and theeffects of grid-supportive incentives.

In the “MAPSEN“ project, we at Fraunhofer ISE are applying
models to investigate how the increasing number of prosumers
affects the electricity markets and grids. The German electrici­ty grid is not designed such that a large number of prosumer

The MAPSEN project is funded by the German Federal Ministry
for Economic Affairs and Climate Action (BMWK).

Solar modules on balconies are becoming increasingly popular.
At Fraunhofer ISE, we are investigating how grid-supportive
integration of this type of prosumer systems can be designed.

Contact

Wolfgang Biener
Phone +49 761 4588-5893
wolfgang.biener@ise.fraunhofer.de70Highlights of our Research: Climate-Neutral Heat and Buildings

New Processes to Extract Raw Materials
from Geothermal Brines
Lithium is a raw material which is essential for the energy tran­
sition and thus of great strategic economic importance. As theglobal lithium demand will increase drastically by 2030, newprocesses are needed to obtain it – particularly as Germany
is currently solely an importer and thus dependent on interna­
tional delivery chains.

In the demonstration systemin the geothermal power
station in Insheim, precipi­tates are separated
by a rotary filter andGerman geothermal springs can be a source, not only of heat,but also of raw materials like lithium, which could contributeto strategic security of raw material resources in future. At
Fraunhofer ISE, we are thus developing process technology
to extract valuable materials from geothermal brines. One
possibility is to concentrate the raw materials, which areusually present in very low concentrations (the lithium content
in the Upper Rhine Valley is about 160 mg/l), to values where
precipitation is possible. The challenge thereby is to control
the crystallization of other materials like silicates so that thesystems do not become blocked.
In the German-Chilean “BrineMine“ project, we have devel­
oped a process technology chain in which the silicate phases
are initially chemically stabilized, before the first concentration
process (by a factor of 8) occurs by reverse osmosis. Whereas
the permeate is available as fresh water, the silicate in theconcentrate is precipitated out by the addition of calcium andthe precipitates are separated off via a rotary vacuum filter.
Further processing and valorization of the silicate is conceiv­
able. The concentrate from the reverse osmosis is then further
concentrated by membrane distillation by a factor of up to 16.
The heat needed to drive the distillation is obtained directlyfrom the geothermal brines. In 2021, we successfully commis­
sioned a demonstration system in a geothermal power stationin Insheim in Rheinland-Pfalz, Germany – and another one inthermal springs in Puyehue, Chile.

transported out.

Furthermore, we are working on the development of highly
selective separation processes which can also run under hightemperature and pressure conditions, so that we can specificallyextract individual elements directly from the brine. To thispurpose, we are cooperating with partners to develop socalled lithium-ion pumps. These are based on an electrodecouple consisting of a lithium manganese oxide electrode (LMO
electrode) and a nickel hexacyanoferrate counter-electrode(NiHCF electrode). When a voltage is applied, lithium is initiallyintercalated within the LMO electrode. When the voltage isreversed, potassium ions are intercalated within the NiHCF
electrode, while the lithium ions are released and are concen­
trated in a recovery solution. We have developed different cellconcepts with electrode areas from 7 cm² to 100 cm² and inves­tigated them in a test rig that was constructed for this purpose.
Now we are working on procedures and methods to produce
and upscale electrodes for large module stacks.

The BrineMine project was funded by the German Federal
Ministry for Education and Research (BMBF).

Test rig with a potentio­

Contact

stat to measure andcharacterize electro­
chemical cells for lithium

Dr. Joachim Koschikowski

extraction from brines.

Phone +49 761 4588-5294
joachim.koschikowski@ise.fraunhofer.de71

Highlights of our Research: Climate-Neutral Heat and Buildings

Digital Method to Completely Represent
the Automation of Building Services
The planning, construction and operation of buildings is
becom­ing increasingly digital. The rising complexity of build­ings can thus be better represented, allowing the energy effi­
ciency to be improved. One methodology to provide digitalized
information on building services plants to all actors involved in
the building is building information modeling (BIM). It allows
access for different tasks at any time throughout all life-cycle
phases of a building, for example for energy-related opera­tion optimization of technical building plant. To achieve this,continuous and systematic connection of the technical building
services, building automation and building operation is needed
via BIM. In the “EnergieDigital“ project, we have cooperated
with RWTH Aachen and the Viega company to develop an
integrated digital description of technical building services anddemonstrated its application in a lighthouse project, the newly
built seminar center, Viega World, in Attendorn, North RhineWestphalia, Germany.
At Fraunhofer ISE, our focus was on developing a method forcomplete, digital representation of the controls for technicalbuilding plant in BIM. The description of the technical build­ing plant functions, which often exists in the form of paper
today, is complemented by a digital model, which is enrichedwith updated information from the planning to the operation
phases. The method encompasses the modeling of the control­
lers, sensors and actuators by semantic web technologies withexisting ontologies and the PLCont ontology that we devel­
oped. Furthermore, the control functions that are implemented
in programmable logic controller (PLC) are modeled digitallyand according to a standardized protocol.

The PLCont ontology allows the control topology to beconnected with PLC functions to obtain a complete,digital representation of the automation.

The digital representation of the automation allows thecomplete building services plant, including its controls, to be
represented as part of the BIM model. In addition, users canaccess an “as programmed” representation of the functions
outside the PLC, allowing planned and actually implemented
controls to be compared. To this purpose, we have developed
a prototypical graphical interface, in which the contents of the
ontology-based description of the controls (digital system dia­gram, control parameters, function description and SPC code)are digitally modeled.
The Viega World seminar center was planned as a climate-neu­tral building and was taken into operation in January 2023. Aspart of the scientific monitoring, we control the targeted andactual performance of the seminar center. As an example, theteam has already shown that the digital representation of thecontrols can simplify and accelerate certain processes of opera­tion surveillance and energy-related optimization of operation.

The EnergieDigital project was funded by the German Federal

The climate-neutral Viega World seminar center

Ministry for Economic Affairs and Climate Action (BMWK).

in Attendorn, North Rhine-Westphalia, Germany.

Contact

Moritz Ihlenburg
Phone +49 761 4588-2377
moritz.ihlenburg@ise.fraunhofer.de72

Highlights of our Research: Climate-Neutral Heat and Buildings

Extending the Application Range for
Thermally Driven Adsorption Chillers
The cooling of buildings and processes already causes signifi­
cant CO2 emissions – and the demand for active cooling isrising. At present, primarily electrically driven, vapor compres­sion refrigeration is applied. However, refrigerants with a highglobal warming potential (GWP) are often used there. The
cooling sector is thus confronted by the challenges to switch
to climate-friendly refrigerants and to reduce the electricity
demand. At Fraunhofer ISE, we are addressing these chal­lenges in several research projects.
Thermally driven cooling technologies (adsorption and absorp­
tion chillers) use waste heat or heat from renewable sources
as the input energy instead of electricity and apply natural re­frigerants such as water or ammonia (GWP = 0). In the SubSie
research cluster, five consortia with partners from science andindustry investigated how sorption systems with water as therefrigerant could address a wider application range, particularly
for temperatures down to freezing point and below (SubSie
platform).
At Fraunhofer ISE, we cooperated with the Fahrenheit com­pany to develop adsorption chillers further (“SubSie-SubKon”
project). In these systems, the refrigerant, water, is evaporated
and adsorbed by a solid sorption agent such as silica gel orzeolite. The basic configuration of an adsorption chiller consistsof three components: firstly, a heat exchanger called an adsorb­­er, which adsorbs the refrigerant vapor from the evapo­
rator in the adsorption half-cycle; secondly, the condenser, inwhich the desorbed water condenses, and thirdly, the evapo­
rator, in which the cooling effect is achieved. In still simpler
configurations, the same heat exchanger operates alternately

as the condenser and the evaporator. The operation mode isthen changed only by switching the temperature levels at theadsorber and evaporator/condenser. The choice of cycling timein operation allows optimization with respect to performanceand efficiency (Coefficient of Performance, COP).
In investigations of innovative evaporators, we demonstrat­
ed that sublimation from a thin ice film can occur without
damage to the heat exchanger and without significant reduc­tion in the thermal performance of the evaporator.
Complete adsorption modules were also investigated at refrig­
eration temperatures of below 3 °C. The water in the evap­
orator freezes occasionally under these operating conditions.
The cooling performance of the module at this operating pointis reduced by about 30 %, for the same COP, compared to theoperating point for an evaporator inlet temperature of 15 °C(refrigeration temperature: about 12 °C). For cycling times
which lead to the same performance under both temperature
conditions, the COP at the low temperatures is about 20 %lower.
At temperatures below 5 °C, applications e.g. in the foodindustry become accessible, which previously could not be
addressed by adsorption chillers.

The SubSie research cluster was funded by the German Federal
Ministry for Economic Affairs and Climate Action (BMWK).

Test rig to characterize adsorption
heat pumps at Fraunhofer ISE.

Contact

Dr. Gerrit Füldner
Phone +49 761 4588-5527
gerrit.fueldner@ise.fraunhofer.de73

Highlights of our Research: Climate-Neutral Heat and Buildings

Developing Heat Pumps with Propane
for the Market
For Germany to become climate-neutral by 2045, the building
sector must make its contribution, as it is currently responsible
for around 40 % of CO2 emissions (including upstream proces­ses). This could succeed with further installation of heat pumps,
as they have a high potential to reduce CO2 emissions in theprovision of heat. The core component of heat pumps is therefrigerant circuit, where a refrigerant flows that evaporates
at a low temperature. To generate heat, the fluid first absorbs
heat from the surroundings; then the refrigerant is compressed
as vapor in a compressor. The problem: At present, most heatpumps use refrigerants with fluorinated gases (F-gases) with alarge global warming potential. The current version of the EU
F-gas Regulation foresees a significant reduction in the use of
substances with high global warming potential in the coming
years. In addition, complete material groups should be incre­
mentally forbidden due to their risk to humans and the environ­ment. This increases the incentive to search for solutions withnatural refrigerants.

Heating power (kW)The goal of the LC150
project was to achieve a

Contact

heating power between

Environmentally friendly alternatives are thus urgently required.
One candidate is propane (R290), which is inexpensive andhas a low global warming potential. In addition, propane hasvery good thermodynamic properties, which enable higher
efficiency than heat pumps with conventional refrigerants.
The challenge: propane is flammable. Thus, extensive safetymeasures apply for its use in heat pumps. If a heat pump ina single-family house, with its usual five to ten kW heating
power, contains more than the prescribed maximum amountof 150 g of refrigerants, it can be installed only if stricter safetymeasures are taken. This could be changed by a new develop­
ment at Fraunhofer ISE. In the “LC150“ project, which has now
been completed, we developed, together with a consortium ofheat pump manufacturers, a propane refrigerant circuit witha reduced amount of refrigerant. A brine-based heat pumpthat was equipped with this circuit already achieves a heating
power of around 12.8 kW with 124 g of propane, and could
thus be installed inside houses without the need for additionalsafety measures. Only 10 g of propane are required per kW ofheating power. That is a new record.
The seasonal coefficient of performance for the heat pump
was determined by weighting data measured in the laboratory
at different, characteristic operating points. It describes theratio of the generated heat to the input electricity and attained
a value of 4.7. Commercially available components wereused for the prototype. An essential part of the concept is toconsistently eliminate regions in the refrigerant circuit that do
not contribute to the heat exchange or pressure adaptation.
This made enormous reductions feasible in the amount ofrefrigerant used. Propane heat pumps should also be used inapartment buildings. In the new “LCR290“ project, we plan
to develop simply applicable and reproducible heat pumpsolutions to replace gas and oil heating in apartment blocks.
Again, propane will be used as the refrigerant, the amountsof refrigerant will be reduced to a minimum and new safetyconcepts will be developed for the remaining quantity of pro­pane. A project consortium with companies from the heatingand housing sectors has been founded to ensure practically
relevant and rapid implementation.

five and ten kW with lessthan 150 g of propane.
Dr. Hannes Fugmann

The project goal was

The LC150 project was and the LCR290 project is being funded by the

Phone +49 761 4588-2353

surpassed.

German Federal Ministry for Economic Affairs and Climate Action

hannes.fugmann@ise.fraunhofer.de

74(BMWK).

Highlights of our Research: Climate-Neutral Heat and Buildings

Efficient Decarbonization of Heating andCooling by Innovative Thermal Storage
Thermal energy storage is becoming increasingly relevant toensure heating and cooling as required, as part of the expan­
sion of energy supplies from renewable sources and topromote flexibility and sector coupling. Innovative approach­es to reduce costs are needed to support the disseminationof storage systems. One possibility is to replace some of theexpensive fluids used in high-temperature storage tanks byinexpensive filler materials. In the “FENOPTHES“ project, wehave further pursued this approach and extended the existing
test rig for molten salt storage by an additional storage tank.
Into this tank, we introduced loose filler materials (photo,right), which consist of different, heat-resistant materials (e.g.,cinders) that are also stable at high temperatures due to abinder containing phosphate. These materials are in directcontact with a molten salt mixture of 60 % sodium nitrate(NaNO3) and 40 % potassium nitrate (KNO3). The working
temperatures usually lie between 290 °C and 550 °C. The
charging and discharging of the system were investigated for
different mass flows and temperatures. In cycling operation, apromising storage efficiency of 98 % and a utilization rate of
73 % were achieved. Altogether, the project results show thatmolten salt storage with filler materials represents an economi­
cally interesting solution for process heat in industry.
Beyond this, we at Fraunhofer ISE also see potential for theisothermal phase transition of phase change thermal materials(PCM) to realize compact storage units with a large capacity
and small temperature differentials in the low-temperature
range between 0 °C and 100 °C. Often, the material proper­
ties of the PCM in its solid state impose limits, for example
with regard to the heat transfer performance. If the PCM isdispersed in a liquid, it can still be pumped in the crystallized

Molten salt / loose
filler material
storage tank after
introduction of
filler material.

state and thus overcomes this limitation. We are therefore
developing PCM slurries (PCS) as a technology for thermal
storage. Due to their high heat capacity, they can be usedsimultaneously as heat storage materials and heat transfer
fluids. If PCS are supercooled, the melting and crystallization
temperatures differ from each other. In the “MINAKRIP“
project, seed materials to reduce supercooling were investigat­
ed experimentally and by molecular-dynamic simulations. The
simulations allow the formation of crystals and the effect of
the crystallization seeds to be understood better at an atomic
level (illustration below). An optimized seed material reduced
the supercooling of a paraffin-water emulsion by 9 K. Buildingon these results, in future it will be possible to develop PCM
slurries with a narrow temperature range, that can thus be
used for numerous further applications.

The FENOPTHES and MINAKRIP projects were funded by theGerman Federal Ministry for Economic Affairs and Climate Action(BMWK).

Phase transition of PCM mole­cules between the solid (left)

Contact

and liquid states (right) in amolecular-dynamic simulation.
∆T

Within yellow frame: PCM

Moritz Kick

crystallites.

Phone +49 761 4588-2097
moritz.kick@ise.fraunhofer.de75

Highlights of our Research: Climate-Neutral Heat and Buildings

Field Measurements to Evaluate the Efficiency and Acoustic
Emissions of Heat Pumps in Existing Single-Family Houses
Heat pumps play an important role in the sustainable trans­
formation of the building sector. However, this transformation
can only be implemented if heat pumps are also introduced
on a large scale into the existing building stock. This is accom­
panied by various challenges – such as access to suitable heatsources and the higher temperatures that are needed to heat
the buildings.

Historical singlefamily house withan outdoor air
heat pump.

Outdoor air heatpump with addi­
tional acoustic

Together with nine heat pump manufacturers and twoenergy utilities, we are addressing several research questions
about applying heat pumps in existing seasonal performancefactor in the “HP-QA in Existing Buildings“ project, which
is running until the end of 2024. To demonstrate the stateof the art and derive optimization opportunities, up to 75
heat pumps are to be experimentally monitored in buildings
dating from 1826 to 2001, and the data will be analyzed
with respect to efficiency and operating behavior. Further
important topics are the measurement of acoustic emissions
by outdoor air heat pumps and investigations of bivalentsystems and self-consumption of PV electricity.
The first interim results of the efficiency analysis refer to themeasurement period from February 2022 to January 2023.
The 21 outdoor air heat pumps that were evaluated during
this period achieved a seasonal performance factor (com­bined generation efficiency for space heating and domestic
hot water) of 3.3, with a bandwidth from 2.4 to 4.1. The sea­sonal performance factor for the eight ground-source heatpumps that are equipped with geothermal probes ranged
from 3.6 to 5.4. Compared to a gas-fired boiler as the refer­ence heat generator, the savings in greenhouse gas emis­
sions were between 18 % and 64 %, based on the lowest
and highest aseasonal performance factors. In 2030, after
about half the usual service lifetime for these heat pumps,
the savings would be between 58 % and 81 % or 77 % and
90 %, depending on the assumption made for the expansion
rate of electricity generated from renewable sources.

measurement
technology in frontof a single-family
house from 1955.

Contact

Danny Günther
Phone +49 761 4588-5371
danny.guenther@ise.fraunhofer.de

76

The interim results from the efficiency analysis alreadydemonstrate the ecological advantages of heat pumps
compared to fossil-fueled boilers. The goal now is to further
expand the data base, to analyze the acoustic measurements
in detail and to derive quality-control measures to ensure
efficient operation of heat pumps, based on deeper analysesof the operating data. In this way, our research can make anessential contribution to the rapid introduction of efficiently
operated heat pumps in the addressed application area.

Highlights of our Research: Climate-Neutral Heat and Buildings

Photovoltaic - Thermal Collectors –New Product Solutions for a Growing Market
Photovoltaic-thermal collectors (PVT collectors) simultaneously
generate electricity and heat from solar energy. Combinedwith a heat pump, these systems can be used to supply spaceheating and domestic hot water efficiently and with only
low CO2 emissions. They are thus an important componentof our research at Fraunhofer ISE on the route to the energy
transition. Compared to heat pumps with an outdoor air unit,
PVT collectors have the advantage that they do not cause any
acoustic emissions, they use the generated electricity them­selves and potentially can operate more efficiently due to thesource temperatures that have been raised by the input ofsolar energy.
In the accredited TestLabs, PV Modules and Solar Thermal
Systems, we at Fraunhofer ISE have comprehensively charac­terized PVT collectors that we have developed and produced,
together with our industrial partners, within joint research
projects. Commercial products and prototypes from different
manufacturers have also been tested in the laboratory. Our
methodological approaches and laboratory facilities proved to
be robust for this application.

Thermal yields for domestic hot water and space heating,electrical yields and electricity consumption of the heat pumpcompressors, as well as monthly average performance factors
PF_0 for a PVT system with covered PVT collectors. Some of theelectricity generated by the PVT collectors can be used directly

Thanks to our industrially relevant research, at Fraunhofer ISE
we have established a prominent position in accompanying
PVT new developments from prototypes up to market intro­
duction. Thus, our services are in strong demand to character­ize modules during a development process and also to test PVT
modules to qualify them for market introduction. The increas­
ing relevance of PVT collectors for building energy supplies
is indicated by the inclusion of further PVT demonstration
systems within the energy monitoring program of the currently
running “integraTE“ project. The information about systembehavior and energy flows can be accessed by our customers
online. This ensures high transparency about the system effi­
ciency and yields, which are important for technology evalua­tion during an early phase in market entry (see graph).

to drive the heat pump. The thermal yields are measured ata balance measurement point between the heat pump andthe thermal storage tank and allocated to space heating or
domestic hot water during the data processing. The PF_0 takes
only the power drawn by the compressor into account for theelectricity balance.

We made an important contribution to the training of trades­
people in the building sector by holding lectures and training
courses, e.g., in the ongoing education programs for energy
advisors and the relevant building trades.
The integraTE project was funded by the German Federal Ministry
for Economic Affairs and Climate Action (BMWK).

Covered PVT collector with a low-

Contacte-coated glass cover during theperformance test on the outdoor
test facility of TestLab Solar Thermal

Dr. Korbinian Kramer

Systems at Fraunhofer ISE.

Phone +49 761 4588-5139
korbinian.kramer@ise.fraunhofer.de77

Highlights of our Research: Climate-Neutral Heat and Buildings

Standardized BIPV Façade Elementswith Integrated Power Electronics
Conventional, commercially available PV modules for roofattached systems are seldom compatible with the dimensions
required in the building stock and they usually do not meet thebuilding code requirements for façades. Above all, the time andeffort to plan and install BIPV façade solutions have been major
barriers up to now. Important aspects here include the electricalconnection of the modules and tolerance to (partial) shading.
The project addresses these challenges by the development ofa BIPV façade solution, in which the dimensions of the modules
have been reduced, on the one hand, such that they match therequirements better. On the other hand, the electrical complexity
is reduced by connecting two or four BIPV modules to a module
inverter to form an electrical unit. The unit is connected directly
to the AC circuit of the building. This modular approach makes
it simpler to plan and install the PV system and often there is noneed for elaborate radiation and shading simulations.
Demonstrator at Fraunhofer ISE. Upper two rows: BIPV modules
with crystalline silicon; center two rows with patterns: modules
with organic PV; the lower three rows originate from the pre­ceding project.

Building roofs and façades are excellently suited for the inte­
gration of photovoltaics (building-integrated photovoltaics,
BIPV). The potential area even exceeds the demand of theenergy transition, they are close to the point of consumption
and they can be used without sealing further land areas.
However, the current expansion rate is too low to contributesignificantly to the success of the energy transition.
The Standard-BIPV-System project aims to facilitate the appli­
cation of façade BIPV and thus to accelerate its dissemination.
The focus is particularly on the existing building stock. The
project is being carried out by Fraunhofer ISE in cooperation
with six partners from industry and research.

Contact

The modules have an area of 1 m x 1.2 m and consist of PV cellsof either crystalline silicon or organic PV. Steel cassettes andmineral fiber panels were investigated as substrates, both beingmaterials that are well known and proven in façade construc­tion. The front surface of the PV cells is protected by a glass
cover. The choice of materials makes architecturally high-quality,
frameless modules feasible. Well-established façade solutions
were used for the sub-structure. In this way, the solar system canbe integrated into a conventional façade, the effort to obtain abuilding permit is reduced and the additional, PV-specific effort
for mounting decreases. Specifically developed, four-pole solar
cables with a plug were used for the electrical connection. They
allow the bypass diodes to be shifted away from the modules
into the ventilated space behind the rear-ventilated rainscreen
façade, reducing their temperature and combining the powerelectronics with the inverter.
We have tested the applicability of the concept with both amobile demonstrator and also a full-scale façade of an existingbuilding at Fraunhofer ISE. Feedback on the demonstrator andalso the experience gained with the existing façade show thatthe basic idea is viable. Further potential for improvement andsolutions were identified and will be investigated in follow-up
projects.

Dr. Jan-Bleicke Eggers

The Standard-BIPV-System project was funded by the German

Phone +49 761 4588-2067

Federal Ministry for Economic Affairs and Climate Action (BMWK).

jan-bleicke.eggers@ise.fraunhofer.de78

Highlights of our Research: Hydrogen Technologies

Corrosion Barrier Layers for Bipolar Plates andPorous Transport Layers in PEM Electrolysers
Strongly corrosive conditions occur on the anode side of apolymer electrolyte membrane (PEM) electrolyser. For thisreason, the incorporated bipolar plates (BPP) and the poroustransport layers (PTL) are usually constructed of titanium.
Titanium ensures that the component is highly resistant against
corrosion. However, the resulting passivation layer leads tocontact resistance that reduces the performance of the elec­
trolysis cell. Thus, platinum is frequently applied as a corrosionprotective layer, which keeps the contact resistance low. At
present, this coating is expensive due to the high material costs
and a production process that has not been optimized.
Within the “H2Giga HyThroughGen” project, we are con­ducting research on inexpensive alternative materials. One
approach is the use of mixtures of noble and base metals. To
facilitate this, we have developed a procedure which allows
quick screening of material mixtures. This is done by co-sput­tering: simultaneous sputtering from two sputtering sources
onto a titanium substrate (upper photo). This results in a
coating with a gradient in its composition along the sub­strate. Subsequently, this substrate can be anodically oxidized
in a single step, and both the composition and the contact
resistance can be determined as a function of the position on
the substrate. The anodic oxidation reproduces the corrosive
conditions in the electrolysis cell.

Production of gradient layer mixtures by co-sputtering.

Our preliminary results already show that addition of 50 % of
the base metal led to the same contact resistance after anodic
oxidation as for the pure noble metal. As a consequence, halfof the noble metal could be saved. We are currently investi­
gating further material mixtures, including materials without
noble metals.
In addition to the material composition, we are also optimizing
the coating process. Within the “H2Giga PEP.IN” project, weare studying the processing chain, starting with the substratecleaning by treatment of the substrate with a linear argon ion
beam immediately before the coating and the coating process.
The results to date have indicated in detail which processing
parameters are particularly relevant and suggest how theprocessing times can be significantly shortened. In addition,
we are developing methods for process control and quality
assurance. In particular, we are working on ex situ corrosion
tests for coated BPPs and PTLs both for fuel cells and for PEM
electrolysers.

Preparation for PTL coating in the sputtering equipment.

The HyThroughGen and PEP.IN
projects are funded by theGerman Federal Ministry

Contact

for Education and Research(BMBF).

Dr. Andreas Georg
Phone +49 761 4588-5993
andreas.georg@ise.fraunhofer.de79

Highlights of our Research: Hydrogen Technologies

A National Hydrogen Strategy
for the United Arab Emirates
That the local demand for hydrogen will be substantial (graphbelow) is one of the results of the strategy process, in which
all of the important hydrogen and energy stakeholders in the
country were involved. Driven on by the net-zero goal for 2050
as well as the global demand for products like “green” steel,sustainable fuels for aviation and the decarbonization of indus­
trial sectors that are difficult to electrify, the UAE can proceedwith the development of projects, as they – unlike other coun­tries – do not first need to establish a market for their product.

Skyline of Abu Dhabi, United Arab Emirates.

The United Arab Emirates (UAE) have developed a nationalhydrogen strategy with which they are pursuing two essen­tial goals: On the one hand, to count among the largest
low-carbon hydrogen producers in the world by 2031, andon the other hand, to advance the decarbonization of local
industry by 2050 with the support of the hydrogen industry.
The government of the UAE entrusted the consultants, GHD
Advisory, and the Fraunhofer Cluster of Excellence Integrated
Energy Systems (CINES), to which Fraunhofer ISE also belongs,
with the preparation of this study.
The UAE will primarily use hydrogen to decarbonize the local
industry – however, the global export market will also be
expanded in parallel. The UAE will establish hydrogen hubs(“H2 Oases”) as a practical approach to accelerate industrial
adoption of hydrogen, cultivate a supply chain, and enableinfrastructure. In addition, investments are being made in
research and development which support the expansion of
the hydrogen value chain.

Contact

The measures proposed in the strategy have the goal of
produc­ing 1.4 million metric tons of low-carbon hydrogenannually by 2031, distributed over different production routes.
At the same time, investments should be made in hydrogen
research and development. For the years after 2031 and along
the path to a decarbonized future, Fraunhofer CINES estimatesthat the production capacity of low-carbon hydrogen of theUAE could amount to 7.5 million metric tons per year by 2040
and almost 15 million metric tons per year by 2050.
In addition to the expected high local demand for hydrogen,the team of authors of the strategy concludes that the UAE
has a very good starting point for exports: The country is
located in an advantageous geographical position to deliver toimportant markets in Europa and Asia, and is equipped withthe corresponding export infrastructure and harbors. Thanks tolarge reserves of natural resources, high capacity for renewableenergy, an international trade and financial center and a quali­
fied and innovative labor force, the UAE are well prepared for
growth in the low-carbon hydrogen industry and for export.

Sector-specific demand
for low-carbon hydrogen in the UAE fromDr. Jan Frederik Braun
Phone +49 761 4588-2331
jan.braun@ise.fraunhofer.de

802031 to 2050.

Highlights of our Research: Hydrogen Technologies

Along-the-Channel PEM Electrolysis Cell for Spatially
Resolved Investigation of Mass Transport Effects
Large-area polymer electrolyte membrane (PEM) electrolysers
with membrane areas of several 1000 cm2 pose high demandson the water and thermal management in the electrolysis cell.
Inhomogeneous conditions are particularly evident along thechannel (AtC) with regard to the consumed water and thegenerated gases, hydrogen and oxygen. At Fraunhofer ISE,
we have developed a segmented AtC PEM electrolysis test cellto conduct spatially resolved investigations of these so-called
mass transport phenomena.
The AtC cell was developed and investigated within the"StacIE" project. The partners involved in this project are
researching the scale-up and industrialization of PEM electrolysis. The project is focusing on the further development ofstack technology for large-volume production capacities.
To analyze the mass transport along the flow channel of a PEM
electrolysis cell on an industrially relevant scale, we constructed
an AtC laboratory cell with a length of 30 cm and a width of
2 cm. The generated hydrogen and thus also the water con­sumption correlate with the applied current density. To create
the most demanding conditions possible, we dimensioned thecell for a current density of up to 600 A (10 A/cm2) and tested
it successfully. We will thus be able to use the cell to analyze
operating points that are anticipated in future with very highhydrogen generation rates. The cell is suitable for investiga­
tions at temperatures up to 80 °C and a differential pressure
up to 10 bar. With the help of a specially conceived measure­ment circuit board, measurements of the current density andtemperature distributions can be made with 120 measurement

Segmented alongthe-channel test cellto analyze local masstransport processes.

contacts. In addition, the cell is divided along the parallel
channel structure by separation of the electrical contact into
ten segments. Electrochemical impedance spectra (EIS) canbe recorded in each of the segments and additionally overthe complete laboratory cell. To separate the processes in thetwo half-cells, three reference electrodes are positioned at the
inlet, in the center and at the outlet of the cell, with which themembrane potential can be determined. For this work, EIS isthe appropriate measurement methodology to separate thepolarization processes such as the mass transport processes.
In the further course of the projects, materials will be charac­terized in the AtC cell which will also be used in future StacIEstack platforms. We aim to gain insight into the internal pro­
cesses along the flow channel thereby. Furthermore, we wantto understand the influence of different structural parametersof porous transport layers on local polarization processes.

Local electrochemical impedance spectra (EIS) to

The StacIE project is funded as part of the H2Giga lighthouse

analyze the mass transport along the cell segments.

project by the German Federal Ministry for Education and Research(BMBF).

Contact

Niklas Hensle
Phone +49 761 4588-2033
niklas.hensle@ise.fraunhofer.de81Highlights of our Research: Hydrogen Technologies

Dimethyl Ether as a Global Hydrogen Carrier

Green, hydrogen-based molecules play a key role in the decar­
bonization of the global energy system. According to current
prognoses, twelve million metric tons of hydrogen shouldbe traded by 2030. One open question is still the transportof hydrogen over long distances (longer than 6000 km, e.g.
from Perth or Cape Town to Rotterdam), as hydrogen pipelines
cannot be used there. Even after energy-intensive compression
or liquefaction by cooling, the volumetric energy density ofhydrogen is low and the transport infrastructure does not yet
exist.
Fraunhofer ISE has identified the potential of dimethyl ether(DME) as a promising, environmentally friendly hydrogen car­rier within the framework of a closed carbon cycle. The DME
is synthesized from CO2 and hydrogen from renewable energy
sources and transported by ship to the energy-importing
country. There, hydrogen can be generated by thermochemicalreforming processes from the DME, and then fed into gas net­
works and pipelines. Carbon dioxide is created as a by-pro­duct, which is then transported in liquid form in the same shipback to the synthesis location and serves as a raw material forsynthesis. A closed CO2 cycle is thus established.
In comparison to alternative hydrogen carriers such as ammo­
nia or liquid organic hydrogen carriers (LOHC), DME offers alarger technical hydrogen storage capacity. As a result, theshipping volume and thus the transport costs can be reduced.
Furthermore, the water which is formed as a by-productduring the DME synthesis can be used for the electrolysis.
Compared to the production and transport of cryogenic hydro­gen, the water demand can be halved in this way, which often

represents a significant advantage in sunbelt regions that are
frequently subject to water scarcity. In addition to the application
as a hydrogen carrier, DME is also an excellent fuel and can also
be used as a basis to product sustainable aviation fuels. We areinvestigating this process in detail within the “SAFari” project.
To increase the efficiency of the processes, the INDIGO technolo­gy, for which Fraunhofer ISE has lodged a patent claim, should beapplied to produce DME. The process simplifies the conventional
production process by applying the reactive distillation concept
under mild reaction conditions and the usage of alternative
catalysts.
Thermochemical hydrogen production from DME takes place atmoderate temperatures compared to fossil-based energy sources
such as natural gas or crude oil fractions. Furthermore, the heat
demand of the catalytic, endothermic reforming reaction stepis 25 % lower. In order to provide commercial DME reforming
plants, process steps such as catalysis, heat generation fromlow-CO2 sources (e.g. electricity and industrial residual heat),hydrogen-CO2 separation processes and the evaporationof water and DME must be adapted. Therefore, we are carryingout experimental and theoretical research on these subjects at
Fraunhofer ISE within the “Power-to-MeDME” project.

The SAFari project is funded by the German Federal Ministry
for Digital and Transport (BMDV). The Power-to-MeDME
project is funded by the German Federal Ministry for Education
and Research (BMBF).

Closed carbon cycle with synthesis of dimethyl
ether (DME) in the exporting country and DME
reforming in importing country.

Contact

Florian RümmeletPhone +49 761 4588-5365
florian.ruemmele@ise.fraunhofer.de
t

82

+

t

t

t

Highlights of our Research: Hydrogen Technologies

Performance and Lifetime of Fuel Cells
after Use of Contaminated Hydrogen
Depending on the production and transport processes, hydro­
gen for Fuel Cell Electric Vehicles (FCEVs) contains impurities
such as hydrocarbons which affect the efficiency and lifetimeof fuel cells. The standard on hydrogen quality, ISO 14687-2,
thus contains specifications of the maximum permissible con­centrations of corresponding contaminants. These maximum
values are determined in comprehensive tests and are incor­
porated in mandatory, national regulations for hydrogen filling
stations. If the demands on the hydrogen purity are high,the levelized costs of hydrogen generation increase and thus
the operating costs of FCEVs. By contrast, if the demands are
low and the concentration of contaminants high, irreversible
damage to the fuel cell could occur in the worst cases.
In the "H2Fuel" project, we are conducting pre-normative
research on contaminated hydrogen in current and future fuelcell configurations in order to justify possible amendments to
ISO 14687-2. Operation data of FCEVs show that frequent loadchanges – which can be simulated, e.g., by the so-called Fuel
Cell Dynamic Load Cycle – and the duration between stoppingand starting a FCEV can support regeneration after contamina­tion. For example, longer breaks between driving phases, e.g.,
overnight after parking the vehicle, can contribute to fuel cellrecovery after strong contamination with carbon monoxide.

This occurs when the system cools down to ambient tem­
perature and water condenses or gas diffuses between theelectrodes: The catalyst poison can then oxidize at the affected
electrode. In turn, this effect, combined with operating
modes which are adapted to contaminated hydrogen, could
justify relaxation of the maximum values for contaminantconcentration.
For economic reasons, however, fuel cell manufacturers often
have the goal of reducing the amount of platinum per stackin the fuel cells, which can negatively affect the tolerance ofthe system to contaminants. Efficiency losses and irreversible
damage to the electrodes appear more frequently if only asmall buffer against the loss of active catalyst surface is avail­able. It is thus important to limit the concentration of each typeof hydrogen contaminant to such a low level that irreversible
degradation does not occur.
In our experimental series, we identified groups of contami­
nants which caused such unexpected, irreversible degradation
effects. With adapted experimental protocols and cell designs
for spatially resolved tests, we investigated the operating modes
which reinforce contamination-induced degradation, in order tolocalize this damage more accurately at the fuel cell level.

The H2Fuel project was funded by the German Federal Ministry
for Digital and Transport (BMDV).

Contact
Cell platform for
spatially resolved
measurements.

Sebastian Prass
Phone +49 761 4588-5310
sebastian.prass@ise.fraunhofer.de83

Highlights of our Research: System Integration

Transformation Paths toward Decarbonizationof the Heating Sector: a Bottom-up Approach
Which role will hydrogen play for future energy supply? Will
we heat with hydrogen? If so, can this reduce the need to
expand the electricity distribution grids? And will municipal
heating planning advance the decarbonization of the heating
sector? These and associated questions were answered byresearchers from Fraunhofer ISE and Fraunhofer IEE in a study
commissioned by the German National Hydrogen Council. In
doing so, they chose a bottom-up approach for the first time,in which they modeled four supply areas in detail, namely Burgnear Magdeburg, Fellbach, Mainz and Westerstede.
For each of the four case studies, prevailing conditions weretaken into account, such as the existing building stock,electricity, gas and heating grids, current electricity and gas
consumption, existing power stations and areas and potential
for photovoltaics, solar thermal and geothermal systems aswell as heat sources and their potential for (large) heat pumps.
We applied the regional, inter-sectoral energy system model,
DISTRICT, of Fraunhofer ISE to model five scenarios for each of
the four case studies. Each scenario assumes that the climate
goals will be reached and depends on variables such as pricedevelopments, availability of technology, infrastructure, thelocal situation of relevant trades and renovation rates.
Across all of the scenarios, it became evident that the expan­
sion of heat pump installations is the most promising strategy
to decarbonize space heating. In particular, heat pumps repre­
sent the only available option to achieve the publicized climate

Transformation of heat generationin the four studied regions for theelectrification scenario (scenario 2 inthe study), classified according
to energy source.

Contact

Dr. Jessica Thomsen
Phone +49 761 4588-5079
jessica.thomsen@ise.fraunhofer.de

84

goals for 2030. Also for the period after 2030, they present
the best solution for distributed space heating supply in every
scenario.
In the district heating and process heat sectors, the scenarios
support the conclusion that a mix of large heat pumps using
different heat sources, hydrogen-driven combined heat andpower and further renewable technologies such as thermal useof solar energy, geothermal systems and biomass will become
established. The selection of technology depends strongly on
the heat sources that are locally available. The potential ofhydrogen as an energy source was evident primarily for district
heating and process heat in all scenarios.
The analysis of the local networks revealed that the demandfor electricity will increase significantly in all the investigatedscenarios and regions and that expansion of the electricity
grid is necessary, regardless of the share of hydrogen use in
the building sector. The modeling chain of Fraunhofer ISE and
Fraunhofer IEE was able to answer diverse questions at differ­
ent levels of detail and thus make an appreciable contribution
to the debate about decarbonization of the heating sector. The
demand analysis of the four selected towns and cities revealed
how complex the transformation of the heating sector is in thespecific urban context and local environment. In addition, it
illustrated the need for integrated energy planning guidance toinitiate decarbonization across all sectors and grids.

Highlights of our Research: System Integration

Joint Building Electricity Supplies: Comparisonof the Economic Viability of On-Site Systems
For the residents of the 21 million apartment buildings in Ger­
many, active participation in the energy transition is possible
only to a limited degree. The Federal Government aims tochange this situation and proposes a model to supply photo­voltaic electricity more simply to apartment buildings: In the“joint building electricity supply” model (gemeinschaftliche
Gebäudeversorgung GG), PV electricity from roof-mounted
systems can be supplied directly to the tenants of an apart­
ment building. The generated PV electricity is distributed
according to an agreed allocation key. Each tenant makes anindividual electricity contract with an energy utility for theremaining electricity supply. In contrast to the “tenant electri­
city model” (Mieterstrommodell), the owner of the PV system
is not required to supply enough electricity to cover a tenant’s
complete consumption. The new regulation promises to ope­
rate with less bureaucratic effort.
In a case study for an apartment building with four apart­ments, we at Fraunhofer ISE have investigated four electricity
supply models with respect to their economic viability:
1. Complete feed-in: the owner of the PV system feeds all of
the generated electricity into the grid; the tenants obtain
their electricity from a utility.
2. Tenant electricity: the PV system owner sells electricity to
the tenants.
Annual electricity costs in an apartment building with fourtenant parties: a family of four, two office workers (full-time inan external office), two office workers (in home office) and apensioner. The four models (1 to 4) assumed are as described in

3. Static joint building electricity supply: the PV system ownerrents system shares to the tenants (fixed allocation of the
PV electricity).
4. Dynamic joint building electricity supply: the PV systemowner rents system shares to tenants (allocation of PV elec­
tricity according to individual consumption).
From the perspective of the PV system operator, all models are
economically viable – the least bureaucratic effort is caused bycomplete feed-in. To make the desired transition away fromcomplete feed-in attractive to the operator, we calculated eco­nomic viability for the following assumptions: Profit increase of
15 % for the PV system owner for all three alternative models(2, 3 and 4) compared to complete feed-in (1). Under thisassumption, the residents have a price advantage for all threealternative models compared to purchasing all electricity froma utility. The annual costs for the residents differ only slightly
between the tenant electricity and joint building electricity
supply models. The most favorable conditions are achievedby the dynamic joint building electricity supply model, as here
the dynamic allocation ensures maximum self-consumption
and the additional costs for accounting and sales of the tenant
electricity model do not occur.
The annual simulation is based on load profiles which we
generated at Fraunhofer ISE using the SynPRO analytic tool.
Overall, the investigation showed that the joint building elec­
tricity supply model is a promising concept to actively include
apartment tenants in the use of self-generated PV electricity.
The model is financially attractive for all parties and can help toreach the stated PV expansion goals.

the main text.

Contact

Paula Oberfeier
Phone +49 761 4588-2220
paula.oberfeier@ise.fraunhofer.de85

Highlights of our Research: System Integration

Decarbonization of the Energy Supply
for Real Estate Property
A decarbonized energy supply is becoming increasingly
important for commercial enterprises – not only in the context
of rising energy prices and supply shortages. Businesses canmove toward climate neutrality by determining and controlling
their energy consumption and emissions and by taking specificmeasures to reduce emissions.
Today, there are many standards to develop, achieve andmonitor decarbonization goals. On contract to the German
Environment Agency (UBA), we have investigated and analyzed
these standards. In doing so, we prepare essential components
for credible climate targets in the short-term, medium-termand long-term perspectives and for a comprehensive emissionsbalance for commercial enterprises. Compensation of emis­
sions should always be the last choice to achieve decarboniza­tion goals. For the energy supply sector, it is advisable tode­­velop transformation routes that allow intermediate goals
to be identified and thus provide decision bases for restructur­
ing the energy system.
Overall, the completed projects reveal very different demandson the energy supply for industrial and commercial real estate.
To evaluate these and identify the options for sustain­able reor­
ganization, the first step is to record the current consumption,
demands and generation potentials on site. In addition to theabsolute consumption values, we identify the required tempe­
ratures for providing heating and cooling. Also, the required

peak power and options to use waste heat are included
when determining the status quo. Different tools are applied
during this process – for example, the waste heat potential
of industrial and commercial units is determin­ed using pinch
analysis. The existing potential to generate electricity and heaton site from renewable energy sources is also determined. On
this basis, different transformation routes are developed which
depend on the scenarios that are assumed for the energy
price development and other boun­dary conditions. For process
heat, the choice of supply technol­ogy depends strongly on therequired temperature level. For temperatures below 200 °C,
for example, high-temperature heat pumps are an option. Ifhigher temperatures are required, there are the options for
direct electrification or a switch to CO2-free fuels such as hyd­rogen or synthetic gases.
Our case studies, including those on the property of PUCARO
Elektro-Isolierstoffe GmbH in Roigheim, show that the poten­
tial for generating photovoltaic electricity must be exploitedas early as possible. On the long term, the heat supply mustalso be completely rebuilt to achieve decarbonization. In order
to meet their remaining electricity demand, enterprises cantemporarily resort to power purchase agreements. Overall,the comparison of possible transformation routes represents agood method to make price risks and their effects on invest­
ment decisions visible.

Potential PV installation areas at the Roigheim site of PUCARO Elektro-Isolierstoffe GmbH. Photo source: Google, Bilder © 2023 AeroWest,GeoBasis-DE/BKG,
Maxar Technologies, map data © 2023 GeoBasis-DE/BKG (©2009).
Roof-installed PV system
Overhead PV system

Contact

Dr. Jessica Thomsen
Phone +49 761 4588-5079
jessica.thomsen@ise.fraunhofer.de

86

Ground-mounted PV system
Already installed PV system

Events in 2024 with Participationof Fraunhofer ISE
January				All information is based on the data that was available at the editorial deadline. We request your understanding
for short-term changes. You will find the current status under www.ise.fraunhofer.de/en/events-and-trade-fairs

87Editorial Notes

Photo Credits

Editorial TeamMarie-Sophie Himmerich, Tobias Mickler
Christina Lotz (Editor-in-Chief)
Editorial Address
Fraunhofer Institute for Solar Energy Systems ISE
Communications
Heidenhofstr. 2
79110 Freiburg, Germany
Phone +49 761 4588-5150
info@ise.fraunhofer.de
www.ise.fraunhofer.dePlease order publications by email.
Reproduction requires the permission of the editors.
www.ise.fraunhofer.de/en/press-media© Fraunhofer Institute for Solar Energy Systems ISE
Freiburg, Germany, 2024
We keep you up to date here:
Internet: www.ise.fraunhofer.de/en
Blog: blog.innovation4e.de/en
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Copyrights
Fraunhofer Energy Alliance: Page 14
INATECH/University of Freiburg: Page 15
Fraunhofer-Gesellschaft: Page 17
badenova: Page 21
iStock.com/Kateryna Novokhatnia: Page 29
ESA/NASA: Page 66
Fraunhofer ISE/Fraunhofer IWM : Page 67
Viega GmbH & Co. KG: Page 72
Bundesverband Wärmepumpe (BWP) e.V.: Page 76
iStock/boule13: Page 80
Friedrich-Alexander-Universität Erlangen: Page 82
Fraunhofer ISE: all other pictures

Translation from German
Dr. Helen Rose Wilson
Layoutnetsyn, Freiburg
Printing
Burger Druck GmbH, Waldkirch

88

Photographers
Michael Eckmann: Page 68
Joscha Feuerstein: Page 81
Myriam Kaiser: Page 49
Guido Kirsch: Page 10
Dirk Mahler: Cover, Pages 2, 8 (Bett, Henning, Glunz, Preu,
Schossig), 24, 25, 31, 33, 35, 37, 39, 41, 43, 45, 46, 48, 49, 50,
51, 56, 58, 69, 73, 81
Bernd Schumacher: Pages 4, 8 (Wittwer, Vormfelde)
Nils Theurer: Page 22
Kai-Uwe Wudtke: Page 8 (Wirth)Fraunhofer Institute for
Solar Energy Systems ISE
Heidenhofstr. 2
79110 Freiburg
Germany
www.ise.fraunhofer.de/en

Annual Report 2023/24