# Presentation: 465689

## Solar EnergyChallenges and Opportunities

*	*with
- Nathan Lewis, Caltech
- Arthur Nozik, *NREL*
- Michael Wasielewski, *Northwestern*
- Paul Alivisatos, *UC-Berkeley*

- George Crabtree
*Materials Science Division*
*Argonne National Laboratory*

## Preview

- Grand energy challenge
- 	- double demand by 2050, triple demand by 2100
- Sunlight is a singular energy resource
- 	- capacity, environmental impact, geo-political security
- Breakthrough research directions for mature solar energy
- 	- solar electric
- 	- solar fuels
- 	- solar thermal

## World Energy Demand

-  EIA Intl Energy Outlook 2004
- http://www.eia.doe.gov/oiaf/ieo/index.html

- energy gap
- ~ 14 TW by 2050
- ~ 33 TW by 2100

- Hoffert et al Nature 395, 883,1998

**Notes:**
Projections of world energy demand by Energy Information Administration
• units are Terawatt-yrs of energy, equivalent to continuous use, day and night, of power over one year
• industrial countries use about half the world’s energy
• US about half industrial countries
• developing countries responsible for largest growth, nearly equal to industrial countries in 2025
• EIA projections are consistent with other studies, notably Hoffert 
• fuel mix is 85% fossil, 39% oil
• mix is projected to be approximately constant to 2025, with gas surpassing coal by 2025, oil remaining at 39% 

## Fossil: Supply and Security

- _[EIA:   ](http://www.eia.doe.gov/oiaf/ieo/index.html)_  _[http:](http://www.eia.doe.gov/oiaf/ieo/index.html)__[//tonto](http://www.eia.doe.gov/oiaf/ieo/index.html)__[.](http://www.eia.doe.gov/oiaf/ieo/index.html)__[eia](http://www.eia.doe.gov/oiaf/ieo/index.html)__[.doe.](http://www.eia.doe.gov/oiaf/ieo/index.html)__[gov/FTPROOT/](http://www.eia.doe.gov/oiaf/ieo/index.html)_
- presentations/long_term_supply/index.htm
- R. Kerr, Science **310**, 1106 (2005)

**When Will Production Peak?**

- gas:   beyond oil
- coal:  > 200 yrs

*production peak*
- demand exceeds supply
- price increases
- geo-political restrictions

**World Oil Reserves/Consumption**
- 2001

- OPEC: Venezuela, Iran, Iraq, Kuwait, Qatar, Saudi Arabia,
- United Arab Emirates, Algeria, Libya, Nigeria, and Indonesia

- http://www.eere.energy.gov/vehiclesandfuels/facts/2004/fcvt_fotw336.shtml

-  uneven distribution
-   insecure access

**Notes:**
• two challenges of fossil fuel: finite supply and atmospheric contamination
• the curve of world oil production tells us a lot about the fossil fuel economy
• it began about 1900 and reached its stride at mid-century
• the oil shortage of the mid 70s and the high oil prices around 1980 stimulated a downturn in production/use
• the first fossil fuel challenge is the finite supply of oil
• the question is not when will the supply run out, but when it will fall short of demand
• historically and in the near future, supply meets demand and the curve of production is also the curve of demand
• at some time, production will peak, while demand continues to rise.  This marks a transition  point in the oil economy when chronic  shortages occur, prices rise, and the world market could become qualitatively different.  This is the “Hubbert’s peak” that some analysts think will drive major revisions of our cultural expectations for energy and especially transportation.
• the graphs shows two projections of the EIA for oil production: satisfy demand until 2016 and  have face moderate shortages after, or satisfy demand until 2037 and face more severe shortages after.  Since reserves are fixed, we are faced with this devil’s dilemma. 
• the projections show in either case that by 2050 we will be producing less oil than we are now, less than half of demand. That will be  major change in our energy economy, as other sources of energy fill the gap or as we simply live with less energy.
• these projections do not take into account the effect of rising prices on reserves: at a higher price, oil that cannot be produced now becomes accessible.  This elasticity in reserves effectively trades shortages for cost.  The market determines how this plays out and it is not possible to project the magnitude of this effect with confidence.
• there is less quantitative information about natural gas reserves, and far less analysis of its production expectations.  The projections we have indicate that its production will peak beyond oil. 
• the world and the US have plentiful coal reserves, enough to last at least 200 years under projected use. 
• the second challenge of fossil fuels is atmospheric pollution.  Greenhouse gases and specifically CO2 are widely thought to produce global warming with major changes in the ocean currents,  the climate of the earth, and rising sea levels. 
• the graph shows the correlation between CO2 in the atmosphere and mean global temperature since 1000 AD.  There is a noticeable correlation.  The effect has accelerated in the past 100 years and both quantities continue to rise at ever increasing slope.
• unlike finite fossil fuel supply, which creates problems in the future, CO2 emissions and global warming are problems that are already in progress.  They are cumulative effects, with today’s conditions dependent on all the CO2 we have put into the atmosphere for the last century and more.  There is an urgency to this problem that may equal or exceed that of fossil fuel supply.  Effects are noticeable: there is far less polar ice at the North Pole than in previous decades, often allowing ships to steam directly over the pole, glaciers are receding, and Hemingway’s famous Snows of Kilimanjaro have nearly disappeared.
• the solution is to capture and store the CO2 emissions that we produce.  It is unlikely that we will opt not to use our fossil fuel reserves as long as they last, so we must find ways to use them without emitting CO2. Creating a viable route to accomplish this is a major scientific challenge.

## Fossil: Climate Change

*J. R. Petit et al, Nature ****399****, 429, 1999 *
*Intergovernmental Panel on Climate Change, 2001*
- _[http://www.ipcc.ch](http://www.eia.doe.gov/oiaf/ieo/index.html)_
*N. Oreskes, Science ****306****, 1686, 2004*
*D. A. Stainforth et al, Nature ****433****, 403, 2005*

*Climate Change 2001: T he Scientific Basis, Fig 2.22 *

## The Energy Alternatives

***The Energy Alternatives***

- Fossil

- Nuclear

- Renewable

- Fusion

- energy gap
- ~ 14 TW by 2050
- ~ 33 TW by 2100

- 10 TW = 10,000 1 GW power plants
- 1 new power plant/day for 27 years

- no single solution
- diversity of energy sources required

## Renewable Energy

***Renewable Energy***

- Solar
- 1.2 x 105 TW on Earth’s surface
- 36,000 TW on land (world)
- 2,200 TW on land (US)

- Biomass
- 5-7 TW gross (world)
- 0.29% efficiency for
- all cultivatable land
- not used for food

- Hydroelectric

- Geothermal

- Wind
- 2-4 TW extractable

- 4.6 TW gross (world)
- 1.6 TW technically feasible
- 0.6 TW installed capacity
- 0.33 gross (US)

- 9.7 TW gross (world)
- 0.6 TW gross (US)
- (small fraction technically feasible)

- Tide/Ocean
- Currents
- 2 TW gross

- energy gap
- ~ 14 TW by 2050
- ~ 33 TW by 2100

## Solar Energy Utilization

- .0002 TW PV (world)
- .00003 TW PV (US)
- $0.30/kWh w/o storage

- natural
- photosynthesis

- artificial
- photosynthesis

- 50 - 200 °C
- space, water
- heating

- 500 - 3000 °C
- heat engines
- electricity generation
- process heat

- 1.5 TW electricity (world)
- $0.03-$0.06/kWh (fossil)

- 1.4 TW biomass (world)
- 0.2 TW biomass sustainable (world)

- 0.006 TW (world)

- 11 TW fossil fuel
- (present use)

- 2 TW
- space and water
- heating (world)

## BES Workshop on Basic Research Needs for Solar Energy Utilization

- April 21-24, 2005

- Workshop Chair:  Nathan Lewis, Caltech
- Co-chair: George Crabtree, Argonne

***Panel Chairs***
- Arthur Nozik, NREL: Solar Electric
- Mike Wasielewski, NU: Solar Fuel
- Paul Alivisatos, UC-Berkeley: Solar Thermal

***Plenary Speakers***
- Pat  Dehmer, DOE/BES
- Nathan Lewis, Caltech
- Jeff Mazer, DOE/EERE
- Marty Hoffert, NYU
- Tom Feist, GE

***200 participants***
- universities, national labs, industry
- US, Europe, Asia
- EERE, SC, BES

***Topics***
- Photovoltaics
- Photoelectrochemistry
- Bio-inspired Photochemistry
- Natural Photosynthetic Systems
- Photocatalytic Reactions
- Bio Fuels
- Heat Conversion & Utilization
- Elementary Processes
- Materials Synthesis
- New Tools

## Basic Research Needs for Solar Energy

*** ******The Sun is a singular solution to our future energy needs***
-    - capacity dwarfs fossil, nuclear, wind . . .
-    -  sunlight delivers more energy in one hour
-          than the earth uses in one year
-    - free of greenhouse gases and pollutants
-    - secure from geo-political constraints

-  ***Enormous gap between our tiny use ***
***of solar energy and its immense potential***
-   - Incremental advances in today’s technology
- will not bridge the gap
-   - Conceptual breakthroughs are needed that come
- only from high risk-high payoff basic research

*** ******Interdisciplinary research is required***
*** ***physics, chemistry, biology, materials, nanoscience
*** ******Basic and applied science should couple seamlessly***

- http://www.sc.doe.gov/bes/reports/abstracts.html#SEU

## Solar Energy Challenges

- Solar electric
- Solar fuels
- Solar thermal
- Cross-cutting research

## Solar Electric

- Despite 30-40% growth rate in installation, photovoltaics generate
*	**	**less* than 0.02% of world electricity (2001)
- 		*less* than 0.002% of world total energy (2001)
- Decrease *cost*/watt by a factor 10 - 25 to be competitive with fossil electricity (without storage)
- Find effective method for* storage* of photovoltaic-generated electricity

## Cost of Solar Electric Power

-   I: bulk Si
-  II: thin film
-        dye-sensitized
-        organic
- III: next generation

*module cost only*
*double for balance of system*

##  Revolutionary Photovoltaics: 50% Efficient Solar Cells 

*** ******Revolutionary Photovoltaics: 50% Efficient Solar Cells ***

- present technology: 32% limit for
-  single junction
-  one exciton per photon
-  relaxation to band edge

- multiple junctions

- multiple gaps

- multiple excitons
- per photon

- nanoscale
- formats

##  Organic Photovoltaics: Plastic Photocells

- opportunities
- inexpensive materials, conformal coating, self-assembling fabrication,
-  wide choice of molecular structures, “cheap solar paint”

- challenges
- low efficiency (2-5%), high defect density, low mobility, full absorption spectrum, nanostructured architecture

- donor-acceptor junction

- polymer donor
- MDMO-PPV

- fullerene acceptor
- PCBM

## Solar Energy Challenges

- Solar electric
- Solar fuels
- Solar thermal
- Cross-cutting research

## Solar Fuels: Solving the Storage Problem

- Biomass inefficient: too much land area.  Increase efficiency 5 - 10 times
- Designer plants and bacteria for designer fuels:
- 	H2, CH4, methanol and ethanol
- Develop artificial photosynthesis

## Leveraging Photosynthesis for Efficient Energy Production

-  photosynthesis converts ~ 100 TW of sunlight to sugars: nature’s fuel
-  low efficiency (< 1%) requires too much land area

***Modify the biochemistry of       plants and bacteria ***
-   - improve efficiency by a factor
-      of 5–10
-   - produce a convenient fuel
-      methanol, ethanol, H2, CH4

*Scientific Challenges*
-  understand and modify genetically controlled biochemistry that limits growth
-  elucidate plant cell wall structure and its efficient conversion to ethanol or other fuels
-  capture high efficiency early steps of photosynthesis to produce fuels like ethanol and H2
-  modify bacteria to more efficiently produce fuels
-  improved catalysts for biofuels production

- hydrogenase
- 2H+ + 2e-  H2

- switchgrass

## Smart Matrices for Solar Fuel Production

-  Biology: protein structures dynamically control energy and charge flow
-  Smart matrices: adapt biological paradigm to artificial systems

*Scientific Challenges*
-  engineer tailored active environments with bio-inspired components
-  novel experiments to characterize the coupling among matrix, charge, and energy
-  multi-scale theory of charge and energy transfer by molecular assemblies
-  design electronic and structural pathways for efficient formation of solar fuels

***Smart Matrices for Solar Fuel Production***

- smart matrices carry energy and charge

## Efficient Solar Water Splitting

***Efficient Solar Water Splitting***

- demonstrated efficiencies 10-18% in laboratory

- Scientific Challenges
-  cheap materials that are robust in water
-  catalysts for the redox reactions at each electrode
-  nanoscale architecture for electron excitation  transfer  reaction

## Solar-Powered Catalysts for Fuel Formation

- new catalysts targeted for
- H2, CH4, methanol and ethanol
- are needed

- Prototype Water Splitting Catalyst

- multi-electron transfer
- coordinated proton transfer
- bond rearrangement

-  “uphill” reactions enabled by sunlight
-  simple reactants, complex products
-  spatial-temporal manipulation of
-    electrons, protons, geometry

## Solar electric
Solar fuels
Solar thermal
Cross-cutting research

- Solar fuels
- Solar thermal
- Cross-cutting research

***Solar Energy Challenges***

## Solar Thermal

- heat is the first link in our existing energy networks
- solar heat replaces combustion heat from fossil fuels
- solar steam turbines currently produce the lowest cost solar electricity
- challenges:
-        	new uses for solar heat
- 		store solar heat for later distribution

## Solar Thermochemical Fuel Production

*high-temperature hydrogen generation**500 °C - 3000 °C *

*                 **Scientific Challenges*high temperature reaction kinetics of 	  	- metal oxide decomposition 	- fossil fuel chemistryrobust chemical reactor designs and  materials

*A. Streinfeld, **Solar Energy*, 78,603 (2005)

## Thermoelectric Conversion

- figure of merit: ZT ~ ( /) T
- ZT ~ 3: efficiency ~ heat engines
- no moving parts

*Scientific Challenges*
- increase electrical conductivity
- decrease thermal conductivity

- nanoscale architectures
- interfaces block heat transport
- confinement tunes density of states
- doping adjusts Fermi level

*nanowire superlattice*

- thermal gradient  electricity

- Mercouri Kanatzidis

## Solar electric
Solar fuels
Solar thermal
Cross-cutting research

- Solar fuels
- Solar thermal
- Cross-cutting research

***Solar Energy Challenges***

## Molecular Self-Assembly at All Length Scales

***Molecular Self-Assembly at All Length Scales***

*                                              **Scientific Challenges*- innovative architectures for coupling light-harvesting, redox, and catalytic components  - understanding electronic and molecular interactions responsible for self-assembly- understanding the reactivity of hybrid molecular materials on many length scales

*The major cost of solar energy conversion is materials fabrication** **Self-assembly is a route to cheap, efficient, functional production *

- biological

- physical

## Defect Tolerance and Self-repair

-  Understand defect formation
-    in photovoltaic materials and
-    self-repair mechanisms in
-    photosynthesis
- Achieve defect tolerance and
-   active self-repair in solar
-   energy conversion devices,
-   enabling 20–30 year operation

**the water splitting protein in  Photosystem II**
**is replaced every hour!***** ***

## Nanoscience

*theory and modeling*
- multi-node computer clusters
- density functional theory
- 10 000 atom assemblies

- manipulation of photons, electrons, and molecules

- quantum dot solar cells

- artificial
- photosynthesis

- natural
- photosynthesis

- nanostructured
- thermoelectrics

*nanoscale architectures*
- top-down lithography
- bottom-up self-assembly
- multi-scale integration

*characterization*
- scanning probes
- electrons, neutrons, x-rays
- smaller length and time scales

## Perspective

***Perspective***

- The Energy Challenge
- 	~ 14 TW additional energy by 2050
- 	~ 33 TW additional energy by 2100
- 	      13 TW in 2004
- Solar Potential
- 	125,000 TW at earth’s surface
- 	36,000 TW on land (world)
- 	2,200 TW on land (US)
- Breakthrough basic research needed
- Solar energy is a young science
-   -  spurred by 1970s energy crises
-   -  fossil energy science spurred by industrial revolution - 1750s

- solar energy horizon is distant and unexplored