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Solar Power

Solar Photovoltaic (PV)

Solar panels, composed of arrays of silicon solar cells, contain no moving parts. When sunlight falls on a semiconductor such as silicon, the light energy energizes the atoms and generates a flow of electrons (electricity as Direct Current) when the circuit is closed. The solar arrays are hooked to an inverter to convert the DC current to Alternating Current required for household appliances, or stored in a battery for later use.

Manufacture of solar cells and panels involves casting of purified silicon into multicrystalline silicon ingots, slicing the ingots into wafers, treating the wafers to produce solar cells, and assembling the cells into finished panels.

Inputs to the production process include raw semi-purified silicon, a mineral oil/grit slurry to cut the polycrystalline silicon into wafers, various acids and bases used to clean the wafers, hydrofluoric acid and chlorotetrafluoroethane (a CFC gas) to etch the surface and edges of the wafers, silicon nitride (SiN) used as an antireflective coating for the cells, silver wire and silver paste used to add electrical wiring and contacts to the cells, and aluminum frames for the final solar panels.

The characteristic blue color of solar cells comes from the antireflective coating, which enhances the cell's capture of sunlight, but makes recycling and reuse of the silicon impractical at the end of the panel's design life.

In addition to rigid solar panels, there is growing interest in flexible, thin-film PV technologies that may be more efficient, use less silicon and be adaptable to additional uses.

Green Jobs Notes:

• April 2009: SolFocus expands its factory in Mesa, AZ that manufactures glass solar reflectors. The convex curved reflectors are used in Concentrator PhotoVoltaic systems. CPV systems use reflectors to concentrate sunlight onto much smaller solar cells, thereby increasing electricity output, decreasing demand for silicon, and making end-of-use recycling of solar panels easier.
• First Solar, Inc., a manufacturer of photovoltaic power systems used for solar energy production, will expand its manufacturing operations and development facility in Perrysburg, Ohio. The company is based in Arizona and makes solar systems for large-scale, grid-connected power generation (not the residential roof-top solar panels many are used to seeing). They use thin-film solar module technology, and many of their installed projects are in Germany.
• March 31, 2009: BP Solar announced that it will trim 140 jobs out of 600 at the Frederick, MD facility. Although manufacture of silicon cells will continue, the assembly of solar panels will be done at lower cost facilities. This illustrates the conflict that may arise between the need to keep prices low to encourage adoption of alternative energy technologies, and the desire to create well-paying green jobs.

Solar Module Recycling: First Solar includes in the sale price an amount that is set aside for collection and recycling of PV modules at the end of their design life. According to First Solar, "[nearly] all components of the module, including the glass and the encapsulated semiconductor material, can be treated and processed into new modules or other products."

Solar Thermal

Solar thermal electricity generation utilizes the sun's heat energy to boil water, and the resulting steam is used to create electricity. Solar collectors, or curved mirrors, are used to focus sunlight onto pipes filled with liquid. The liquid circulates through a steam generator, the steam turns a turbine generator, which creates electricity. Unlike PV solar power, thermal energy can be stored for some time until electricity generation is needed.

FPL Energy owns and operates 7 commercial-scale solar thermal plants in the Mojave Desert, including 5 at Kramer Junction, CA. These facilities, called Solar Electric Generating Systems (SEGS) include fields of parabolic mirrors that collect and focus sunlight to heat fluid in pipes. The heated fluid (a synthetic oil called therminol) is used to boil water to create steam, and the steam turns turbine-generators to create electricity. The SEGS also have auxiliary natural gas boilers to generate electricity during non-solar hours. The facilities are connected to the electric grid, and power is sold to Southern California Edison.

FPL's Solar Electric Generating Systems at Kramer Junction, CA in the wind-whipped, sunny Mojave Desert features rows of parabolic solar mirrors.

Green Jobs Notes:

• In June 2008, the first solar thermal power manufacturing plant in the United States began production outside Las Vegas. The facility, owned by Ausra, manufactures solar reflectors.

In addition to commercial-scale generation of electricity from the sun's heat energy, roof-top solar thermal systems are often used to heat hot water for homes.

Additional Information Resources

• Solar Electric Power Association
• Solar Energy Industries Association (SEIA)