JAPAN’S LONG-PLANNED PHOTOVOLTAICS:SPACE-BASEDSOLAR POWER
AND PEROVSKITESOLAR CELLS

Solutions are emerging to conquer solar power’s shortcomings, namely, limited installation sites
and low-capacity utilization rates. Japan is spearheading the development of two promising technologies
to make optimal use of both the Earth and space and fully harness the Sun’s power as electricity:
space-based solar power and next-generation flexible solar cells.
Sunlight illuminates and warms
the Earth and is the ultimate
source of all biological activity.
Solar power, which converts theSun’s energy into electricity, is
one method of generating powerthat the world is increasingly
focusing on in the effort to createa decarbonized society.
Although solar power has beenin practical use since the 1970s, it
has yet to become a major source ofpower worldwide. That stems fromthe dearth of appropriate locations
for installing solar panels, alongwith the low-capacity utilization
rate as power generation falls
off, such as at night, during bad

Left: Diagram of a space-based solar power (SBSP). An antenna located at sea receives microwaves transmitted from a satellite in geostationary orbit andconverts them into electricity. Microwave irradiation requires an accuracy of less than 0.001º in angular error. SHINOHARA LAB., KYOTO UNIV.
Right: Image of a perovskite solar cell (PSC) wall installation. NEW ENERGY AND INDUSTRIAL TECHNOLOGY DEVELOPMENT ORGANIZATIONProfessor SHINOHARA Naoki of Kyoto
University’s Research Institute for Sustainable
Humanosphere specializes in wireless powertransmission, space solar power stations, andmicrowave processing. He has served as amember of the Japan National Space PolicyCommittee and as chair of the Wireless Power
Transfer
Consortiumfor
PracticalApplications. SHINOHARA LAB., KYOTO UNIV.

weather, or when the panels getdirty.
To maximize the use of solar
energy and overcome thosedrawbacks,
two
promisingtechnologies have been developed:
space-based solar power (SBSP)
and next-generation f lexible
solar cells. Japan is making steadyprogress toward the practicalimplementation of both.
The SBSP project involves thespace launch of satellites equippedwith giant solar panels measuring
2 km2, converting the generated
electricity into microwaves that arethen transmitted wirelessly to theground. Since the satellites will beable to generate power day or night
regardless of the weather, they will
boast a high-capacity utilization
rate of at least 90%, generating an
estimated five to 10 times more
power than ground-based solar
panels, whose capacity utilization
rate is a mere 15% or so. Eachsatellite will generate 1 million
kW of electricity, equivalent to theoutput of a nuclear power plant.
Microwaves—atypeof
electromagnetic wave, used now
daily in microwave ovens andcommunications equipment, thatthe system will use to transmit
the power to the ground—canpenetrate clouds and rain if theoptimum frequency is selected,
making them virtually free fromweather interference. Since thetransmission would be wireless,moreover, the target destination
can be changed as needed. The
SBSP concept was first proposedin the U.S. back in 1968, but
research has stalled due to several
technical and cost-related issues,
such as the difficulty in establishinghighly efficient systems for power
generation and transmission andthe transport and assembly ofgiant solar panels. With recent
technological advances, however,
SBSP technology has begun togarner renewed attention aroundthe world.
Meanwhile, Japan has been
continuing
SBSP
researchfor several decades throughindustry-academia-government
collaboration. Kyoto University
has already taken the lead inestablishingwireless
power
transmission technology using
microwaves, a fundamental elementof SBSP. In 1990, the university’s
Professor SHINOHARA Naoki
was inspired to enter the field byhis mentor at the time, Professor
MATSUMOTO Hiroshi, whosaid, “SBSP is a technology thatwill enable the human race tosurvive for the next 10,000 years.”
Looking back on his old mentor’s
declaration, Shinohara said, “Ifthe Earth’s population continues
to grow, so will the amount ofelectricity consumed, and thegeneration capacity on the groundwill be insufficient to supply thenecessary power. That’s why weneed to go into space.”
Since the 1980s, Japan
has conducted many SBSP
experiments in outer space andaccumulated a large amount ofrelevant data, even when researchhas been suspended elsewhere. In
1983, it conducted the Microwave
Ionosphere Nonlinear Interaction
eXperiment (MINIX), whichtransmitted power from one rocket

The photo shows a microwave wireless powertransfer experiment from an airship to theground, conducted by Kyoto University in2009. Due to its ability to send and receive
power over longer distances than othercontactless power-transfer methods, thetechnology to wirelessly transmit power withmicrowaves shows promise for use in a variety
of applications on the ground, such as
supplying power to disaster areas where
infrastructure has been disrupted.
SHINOHARA LAB., KYOTO UNIV.

PSCs are made by coating orprinting materials on a thin
substrate such as plastic. They
are considered to have higher
production efficiency thanexisting solar cells.
SEKISUI CHEMICAL

to another in space plasma for the
first time in world history. Later,in 1993, the country conducted a
successful rocket experiment using
the then newly developed phasedarray antenna for more accurate
power transmission in space plasma.
Japan also has strong enoughcapabilities in satellite system design
to maximize power generation
efficiency and accurately transmit
power to the ground.
Shinohara said, “SBSP has beenincorporated into the Japanese
government’s Basic Plan on Space
Policy since it was first formulated
in 2009. I’ve been researching
SBSP technology for many years,
and now that there is global
attention on it, I feel it will truly
work out.” The current plan has
set a goal of conducting a spaceto-ground power transmission
experiment by fiscal 2025. The
California Institute of Technology
already successfully conducted
such an experiment earlier this year,
but Japan is aiming to transmit
power with even greater precision,
with the focus on developing
beam-control technology toaccurately send microwaves froma fast-moving satellite in low orbit
to a receiving antenna on theground. Progress is steadily being
made toward the goal of creatinga feasible SBSP around the middleof the century.
On the other hand, the social
implementation of “flexible solarcells,” namely perovskite solar
cells (PSCs)—a technology thatwill expand the area available
for generating solar power on
the Earth—is currently being
demonstrated. Utilizing the Green
Innovation Fund establishedby the Japanese government,
several companies and research
institutes are working together todevelop practical applications andpopularize PSCs.
PSCs were invented in Japan,
with the first research paper
published in 2009. PSCs are filmshaped solar cells made of a material
whose crystal structure resembles
that of a mineral called perovskite.
The cells are thin, lightweight,
and flexible, in contrast to today’s
mainstream silicon solar panels,
which are thick and rigid, andthus face restrictions on where
they can be installed. Meanwhile,

the power-generating layer of a
PSC is less than 1μm thick, morethan 100 times thinner than a
traditional silicon solar cell. PSCs,
which are about one-tenth theweight of ordinary solar cells, canthus be installed in places whereconventional solar panels cannot,
such as on the exterior walls of abuilding or on curved surfaces.
Onecompany
currently
developing PSCs is SEKISUICHEMICAL CO., LTD., amajor chemical manufacturer.
One problem with PSCs is theirpoor durability; outdoors, theyquickly degrade owing to moisture,oxygen, and ultraviolet light. Thisis where SEKISUI CHEMICAL’s
technological expertise comes
into play. MORITA Takeharu,
Director of the Perovskite Solar
Cell Group at the company’s R&DCenter, said, “Our strengths lie
in our sealing technology that
protects precision equipment fromdust and moisture, as well as ourfilm sheet manufacturing. We havethe largest global share of liquid
crystal sealants, as well as interlayer

MORITA Takeharu (right), Director ofSEKISUI CHEMICAL’s R&D Center
Perovskite Solar Cell Group, is shown holding
a PSC along with KOGA Meiko (left),
Executive Officer of the company’s Corporate
Communications Department. SEKISUI CHEMICAL

films for automotive laminatedglass. We are also working withcustomers and suppliers to develop
construction and installation
techniques. Our development
now is geared toward future
maintenance and replacements.”
With more than 30 companies
andlocalgovernments
collaborating, many demonstration
tests and joint-research projects
are underway. In April 2024, amajor IT company in Tokyo plans
to install PSCs on the walls of adata center for a demonstration
test. In order to control theirindoor temperature and prevent
intrusion, data centers normally
have few windows, which makes
a substantial portion of their wall
surfaces suitable for installing
PSCs. Data centers also consume alot of power because they operatemany servers, so decarbonization
is an important issue. After theconclusion of the demonstration
tests, the IT company intends toinstall PSCs at 16 of its data centers
across Japan.
Other pilot projects are in theplanning and implementation
stages at sewage treatment plants,
thermal power plants, railroad
facilities, public facilities, andelsewhere to investigate durability
and power-generation efficiency
under various conditions. Afterthe trials are completed, the PSCs
will be deployed to other similar
facilities nationwide. KOGA
Meiko, Corporate Communication
Department Head and Executive
Officer at SEKISUI CHEMICAL,
said, “For over 75 years, wehave been working to solve
environmental issues throughour businesses and products, but
perovskite solar cells seem to holdparticularly great promise. Throughthis technology, we hope tocontribute to the building of social
infrastructure that helps give people
around the world peace of mind.”This April, at the Ministerial
Council on Renewable Energy,
Hydrogen and Related Issues,
PrimeMinister
Kishidaannounced that Japan aims tointroduce PSCs to society as soon
as possible, instead of waiting
until 2030. Commenting on thatannouncement, Morita said, “It isbeyond anything I ever expectedthat our company and our country
would be pursuing the same goal,”
but added, “We have to makea nationwide effort to develop
feasible PSCs as quickly as possible
and spread them across the globe.”
The search for more sustainable
and efficient methods of power
generation is indispensable forhumanity’s survival over the next
10,000 years and beyond. Moreover,given the unstable state of global

In May 2023, a PSC test measuring the powergeneration efficiency of PSCs and verifying
their corrosion resistance performance beganat the Morigasaki Water Reclamation Center, asewage treatment facility in Tokyo and thelargest water reclamation facility in Japan.
Tokyo Governor KOIKE Yuriko (foreground,left) and SEKISUI CHEMICAL President
and Representative Director KATO Keita(foreground, right), who is a co-researcher,mount a PSC to a pipe.
TOKYO METROPOLITAN GOVERNMENTaffairs, energy security has become
an urgent issue for every country. It
will become increasingly important
to introduce renewable energy
sources that do not require fuel, andto diversify energy sources. Japan’s
efforts to harness the potentialof solar power, a well-known
renewable energy source, will shine
a light on humanity’s future.

PSCs produced by SEKISUI CHEMICAL, which were also exhibited at the International Media
Center (IMC) at the G7 Hiroshima Summit. SEKISUI CHEMICAL