Solar Energy Utilization

Transcription

1 Solar Energy Utilization H 2 O O 2 CO 2 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. sugar natural photosynthesis C space, water heating C heat engines electricity generation process heat Solar Electric.001 TW PV $0.30/kWh w/o storage Solar Fuel 1.4 TW solar fuel (biomass) Solar Thermal TW 1.5 TW electricity $0.03-$0.06/kWh (fossil) 11 TW fossil fuel (present use) ~ 14 TW additional energy by TW space and water heating

2 Solar Paint d Fooling inexpensive particles into behaving as single crystals O ( O ) n polymer donor MDMO-PPV fullerene acceptor PCBM O OMe inexpensive processing, conformal layers

3 Revolutionary Photovoltaics: 50% Efficient Solar Cells present technology: 32% limit for single junction one exciton per photon relaxation to band edge lost to heat E g 3 I 3 V multiple junctions multiple gaps multiple excitons per photon hot carriers rich variety of new physical phenomena understand and implement

4 Energy Conversion Strategies Fuel Light Electricity CO 2 Sugar Fuels SC Electricity e H O 2 O H 2 2 sc SC O 2 Photosynthesis H 2 O Semiconductor/Liquid Junctions Photovoltaics

5 Lessons from Photosynthesis

6 Nanorod-based Membrane Offers Several Advantages Tandem junction system Increased light absorption Nanorod geometry orthogonalizes directions of light absorption and carrier collection Long nanorods can absorb all incident light Carriers need only travel radially to the nanorod sidewalls to be separated and collected Greater flexibility in materials selection Potential candidates: WO 3 and Si

7 Structure Radial Advantage L D purity materials cost Impure material but high performance

8 Si Rods by Vapor-Liquid-Solid (VLS) Growth Silicon freezes out H 2 + SiCl 4, ~1000 C Single crystals Growth direction controlled by substrate High growth rates (up to microns/s) Inexpensive gas phase precursors B. M. Kayes, M. A. Filler et al., App. Phys. Lett. 91, (2007) R. S. Wagner and W. C. Ellis, App. Phys. Lett. 4, 89 (1964)

9 Copper-Catalyzed Si Wire Arrays 15 m 250 m 3 m array, 500 nm Cu, T growth = 1000 o C, P growth = 760 Torr, 10 min growth, 2 mole % SiCl 4 in H 2 Copper produces wire arrays that are structurally equivalent to gold.

10 Large Area Rod Array Removal Top-down view Side view 115 μm Large area arrays (> 1 cm 2 ) transferred in one piece. Conformal coating from top to bottom of rods

11 Flexible Inorganic-Polymer Composites

12 Initial Solid-State PV Devices Add transparent top contact: p ~ 7% efficient Putnam, Boettcher, et. al. In Prep.

13 Deep Integration on Nanoscale: New Functionality H Relaxes + H 2 Catalyst Activity Requirements o CoO x o alkaline acidic H 2 O O 2 o CoO x (neu) o CoO x (neu) h h M n+ M n+ M n+ M n+

14 Solar-Powered Catalysts for Fuel Formation chlamydomonas moewusii 10 µ photosystem II hydrogenase 2H + + 2e - H 2 oxidation 2 H 2 O 4e - reduction CO 2 O 2 Cat 4H + Cat HCOOH CH 3 OH H 2, CH 4

15 Solar Energy Challenges Solar electric Solar fuels Solar thermal Cross-cutting research

16 Z T Thermoelectric Conversion thermal gradient electricity figure of merit: ZT ~ ( / ) T ZT ~ 3: efficiency ~ heat engines no moving parts Scientific Challenges increase electrical conductivity decrease thermal conductivity nanowire superlattice Bi 2 Te 3 /Sb 2 Te 3 superlattice CsBi 4 Te 6 Zn 4 Sb 3 PbTe/PbSe superlattice TAGS LaFe 3 CoSb 12 LAST-18 AgPb 18 SbTe 20 Si Ge nanoscale architectures interfaces block heat transport confinement tunes density of states doping adjusts Fermi level 0.5 Bi 2 Te 3 PbTe RT Temperature (K)

17 Solar Land Area Requirements 3 TW

18 Control of Materials Properties Through Nanoscience biological physical mechanical Self-assembly of complex structures O 2 H 2 Hydrogen from water and sunlight - + demonstrated efficiencies 10-18% in laboratory

19 Solar Thermochemical Fuel Production high-temperature hydrogen generation 500 C C concentrated solar power concentrated solar power M x O y Solar Reactor M x O y x M + y/2 O 2 M 1/2 O 2 fossil fuels gas, oil, coal Solar Reforming Solar Decomposition Solar Gasification H 2 O Hydrolyser x M + y H 2 O M x O y + y H 2 H 2 M x O y CO 2, C Sequestration A. Streinfeld, Solar Energy, 78,603 (2005) Scientific Challenges high temperature reaction kinetics of - metal oxide decomposition - fossil fuel chemistry Solar H 2 robust chemical reactor designs and materials

20 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

21 Summary Need for Additional Primary Energy is Apparent Case for Significant (Daunting?) Carbon-Free Energy Seems Plausible (Imperative?) Scientific/Technological Challenges Provide Disruptive Solar Technology: Cheap Solar Fuel Inexpensive conversion systems, effective storage systems Policy Challenges Energy Security, National Security, Environmental Security, Economic Security Is Failure an Option? Will there be the needed commitment?

22 Solar Energy Challenges Solar electric Solar fuels Solar thermal Cross-cutting research