Solar Energy Physics 52

Outline Basics of today’s power generation The Sun Photovoltaic Cell Modules and systems A little economics Conclusion Quiz

Power Generation Current energy usage by mankind 7 x W

Renewable and Non-Renewable energy Sources Non-Renewable –Oil –Natural Gas –Coal –Nuclear Renewable –Hydro-electric –Wind –Bio Fuels –Solar Direct heating Photo-Voltaic

Current World Energy Sources Other includes wind and solar power

The Sun

Solar Power The total power from the sun is about 4 x W a) How much total power hits the earth? b) What is the power density (W/m 2 )at the top of the earth’s atmosphere? References on Solar energy: 1) Review paper by L. Kazmerski, of National Renewable Energy Laboratory, Golden, CO 2) Fundimentals of Renewable Energy Processes By Also DaRosa (Stanford)

Solar Power a) How much total power hits the earth? Power e = P S  R e 2 /4  D 2 P e = 1.7 x W Total human energy usage = 7 x W

Solar Power b) What is the solar power density (W/m 2 )at the top of the earth’s atmosphere? Power Density e = P S /4  D 2 Power Density e = 1360 W/m 2 (Solar Constant)

Solar Power c) What is the solar power density at the surface of the earth? Step 1: Average over all latitudes, day and night is ¼ solar constant Step 2: Average attenuation due to clouds and other absorption is about 50% Average Insolation = 1360W/m 2 x ¼ x ½ = 174W/m 2

Average Insolation

Photovoltaic Cells

Photovoltaic Cell

Semiconductor material that absorbs photons with energy greater than the material bandgap pn junction with bias allows current to be generated from the electron hole pair that is generated by the absorbed material > 95% of todays cells are simple silicon

The silicon solar cell, invented in 1955, quickly became the standard for space power. Solar Cells

Solar Power d) What size (m 2 ) photovoltaic cell would you need to power your house or apartment? Need to assume something for Photovoltaic efficiency

Efficiency of PV Cells

Historical Silicon PV Efficiency Manufacturers Concentrated on Cost Reduction During this Period

Photovoltaic Cells Multi-junction cells now have demonstrated efficiencies approaching 40% and are for sale at rated efficiency of >25% Multi-junction cells lead to high cost semiconductor devices. Concentrator systems allow dramatic reduction in the amount of active material

Concentrating Solar Power Example of a concentrator system for solar cells comes from SolFocus Allows for a 500x reduction in the amount of PV area needed

Solar Power d) What size (m 2 ) photovoltaic cell would you need to power your house or apartment? Power Generation = Insolation x PV efficiency = 200W/m 2 x 0.25 =50W/m 2 Energy/Day= 50W/m2 x 24 hr =1.2KW-hr/m 2 My house uses 1000KW-hr/mo. or 33KW-hr/day Area = 33KW-hr/day/1.2KW-hr/day m 2 Area = 28m 2

Solar Power One More Idea Off Grid: Your power system must store energy for use at night and cloudy days. Leads to expensive battery systems. It must also be robust enough to meet peak demand (Examples: Boats, Satellites, very remote sites) On Grid: Your power system shares its power with the public or private utility, selling power when generation exceeds demand and buying power when generation is less than demand.

Distributed Generation Strategies are Shaping the Future Distributed Power Generation will be the Future Architecture 1900’s 2000’s

Economics and projections

Silicon Roadmap Cost Solar Panel Price Drops by 19% With Each Doubling in Manufacturing Capacity PV Experience Curve Rough Rules of Thumb Prices halve every decade Market size increases ten-fold every decade Silicon Shortage 2006 $3.50/W

Silicon Roadmap Cost Incremental Improvements in Silicon Technology will Continue to Drive Solar Panel Price Reduction Continuous Cost Reduction Retail Parity

Photovoltaic Production

Market Growth Source: Strategies Unlimited

Walldürn, Germany – 8.0 kW

Osaka, Japan – 5 kW

Microsoft Silicon Valley Campus

Surprise Geothermal Solar Biomass Wind Nuclear Hydro Gas Oil &NGL Coal Trad. Bio. Exajoules Source: Shell, The Evolution of the World’s Energy Systems, 1995 Renewable Energy Drivers: Climate Change Fossil Fuel Depletion Sources of Energy 50 years from now

Conclusions

Solar power future Environmental –With the pressure to reduce greenhouse gasses people and governments will invest in solar energy to reduce costs and expand deployment Political –Strong desire in US to reduce dependence on foreign sources of energy (oil) Economic –Cost of oil and natural gas will continue to increase lowering the bar for alternative energy to compete economically

Venture Capital want into the act New Solar Energy companies –Better materials for the cell –More efficient cell production –Less us of silicon material –New mounting techniques Over next decade start-up companies will compete with multi-national companies until technology settles down to a pure production cost race