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 1012 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

39%

23%

23%

7%7% 1%

Oil

Gas

Coal

Nuclear

Hydro

Other

Other includes wind and solar power

The Sun

Solar Power

The total power from the sun is about 4 x 1026W

a) How much total power hits the earth?

b) What is the power density (W/m2)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 ProcessesBy Also DaRosa (Stanford)

Solar Power

a) How much total power hits the earth?

Powere = PSRe2/4D2

Pe= 1.7 x 1017W

Total human energy usage = 7 x 1012W

Solar Power

b) What is the solar power density (W/m2)at the top of the earth’s atmosphere?

Power Densitye = PS/4D2

Power Densitye = 1360 W/m2

(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/m2 x ¼ x ½

= 174W/m2

Average Insolation

Photovoltaic Cells

Photovoltaic Cell

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 (m2) 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 SolFocusAllows for a 500x reduction in the amount of PV area needed

Solar Power

d) What size (m2) photovoltaic cell would you need to power your house or apartment?

Power Generation = Insolation x PV efficiency

= 200W/m2 x 0.25

=50W/m2

Energy/Day= 50W/m2 x 24 hr =1.2KW-hr/m2

My house uses 1000KW-hr/mo. or 33KW-hr/day

Area = 33KW-hr/day/1.2KW-hr/day m2

Area = 28m2

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 FutureDistributed Power Generation will be the Future Architecture

1900’s 2000’s

Economics and projections

Silicon Roadmap Cost

1

10

100

1 10 100 1,000 10,000 100,000

Cumulative Production (MW)

Module Price ($/W) ($2002)

Historical

Projected

1980$21.83/W

1990$6.07/W

2000$3.89/W

2010$1.82/W

2013$1.44/W2002 Roadmap

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 Cost1

10

100

1 10 100 1,000 10,000 100,000

Cumulative Production (MW)

Module Price ($/W) ($2002)

Historical

Projected

1980$21.83/W

1990$6.07/W

2000$3.89/W

2010$1.82/W

2013$1.44/W2002 Roadmap

Incremental Improvements in Silicon Technology will Continue to Drive Solar Panel Price Reduction

Continuous Cost Reduction

Retail Parity

Photovoltaic Production

Market Growth

0

500

1,000

1,500

2,000

2,500

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Industry Shipments (MW)

On-Grid Utility

On-Grid Commercial

On-Grid Residential

Indoor

Consumer Power

Remote Habitation

Remote Industrial

Source: Strategies Unlimited

Walldürn, Germany – 8.0 kW

Osaka, Japan – 5 kW

Microsoft Silicon Valley Campus

18801860

500

0

1000

1500

1900 1920 1940 1960 1980 2000 2020 2040 2060

Surprise

Geothermal

Solar

Biomass

Wind

Nuclear

Hydro

Gas

Oil &NGL

Coal

Trad. Bio.

Exa

jou

les

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