Solar Energy Raymond F. Carl
History of Solar Energy • Types of Solar Energy Technologies • Passive • Concentration • Photovoltaic • Photovoltaic Cell (Solar Cells) • Materials and Efficiency • Inorganic • Organic • Concerns about risks of toxic materials in PV Cells
The History of Solar Energy • Greeks used passive solar to heat Buildings (400 BC) • Romans improved by using glass to trap heat in the buildings and green houses (100 AD) • 1700: Antoine LaVoisier built a solar heater • 1839: French physicist Antoine-Cesar Becquerel observed that shining light on an electrode submerged in a conductive solution would create an electric current. • 1860: The First Solar Motor, heated water used to drive a steam motor, Auguste Mouchout • 1883: American Charles Fritts described the first solar cells, which was made from selenium wafers
The History of Solar Energy • 1900: The photoelectric effect was discovered. • 1904: Henry E. Willsie first use of solar energy at night. • 1916: Millikan provided experimental proof of the photoelectric effect • 1918: Polish scientist Czochralski developed a way to grow single-crystal silicon. • 1941: American Russell Ohl invented a silicon solar cell • 1954: Bell Labs researchers Pearson, Chapin, and Fuller reported their discovery of 4.5% efficient silicon solar cells • 1950’s: Solar cells developed for satellites • 1960: Hoffman Electronics achieved 14% efficient PV cells. • 1973: OPEC Energy Crisis causes US to re-examine use of renewable energy sources; federal and state tax credits result in rapid growth for a new solar industry.
Passive • Direct Solar Gain • South facing large windows • Floors, walls, ceiling used to trap heat. The heat is released at night
Passive • Indirect Solar Gain • Thermal storage materials are placed between the interior habitable space and the sun • Can use vents in wall to help circulate hot air through room
Passive • Isolated Solar Gain: • Uses a fluid (liquid or air) to collect heat in a flat plate solar collector attached to the structure.
Concentration • Power towers • Large field of mirriors is used to concentrate the sunlight. • Concentrated Sunlight is used to heat molten salt
Concentration • Trough Collectors • Uses parabolic mirrors to heat a fluid in an absorbing tube. • Hot fluid is used to boil water to run a steam generator.
Photovoltaic Cells (Solar Cells) • Photoelectric effect • PN junction directly converts sunlight into electricity. • Electricity can be stored for later useage or used on demand.
Photovoltaic Cells (Solar Cells) • Multiple PN junction Cell has multiple transparent layers • Top layer absorbs the high energy light and passes rest through
Photovoltaic Cells (Solar Cells) • Solar Cells transform light to electricity • Controller regulates were the charge is directed • Batteries store the energy • Inverter converts from DC to AC
Photovoltaic Cells (Solar Cells) Inorganic Materials • Thick Crystalline Materials • Crystalline Silicon • Single-crystal • Multicrystalline • Edge-defined film-fed growth • Dendritic • Gallium Arsenide (GaAs)
Photovoltaic Cells (Solar Cells) Inorganic Materials • Thin Film Materials • Amorphous Silicon (a-Si) • Cadmium Telluride (CdTe) • Copper Indium Diselenide (CuInSe2, or CIS)
Inorganic Materials • Concerns: • Use of toxic metals like Cadmium • Use of toxic gasses in the manufacturing of PV, silane, hydrogen selenide • Can the materials be recycled or are they destined for landfills
Inorganic Materials • Concerns Answered • Cd is produced as a byproduct of Zn production and can either be put to beneficial uses or discharged into the environment • CdTe in PV is much safer than other current Cd uses. • CdTe PV uses Cd 2500 times more efficiently than NiCd batteries • Occupational health risks are well managed - • Continuous vigilance is required • Absolutely no emissions during PV operation • Risk from fire emissions is minimal • Disposal of spent modules is an environmental issue – • Reducing the amount of CdTe will alleviate the problem • Recycling will resolve most environmental concerns • Burning of Coal produces 140 g Cd/GWh in fine dust • Burning of Coal produces 2 g Cd/GWh be emitted from the stack (for plants with perfectly maintained electrostatic precipitators or baghouses operating at 98.6% efficiency
Inorganic Materials • Concerns Answered • Manufacturers use gas handling systems to reduce risk, and use careful engineering and administrative controls to prevent exposure of workers or the public. • Landfill leaching is a modest concern only, because PV materials are largely encased in glass or plastic and many are insoluble. • Because of dispersed use, and small amounts of semiconductor material per cell, PV recycling will be challenging. Machinery for dismantling modules for recycling has been developed, and recycling systems for batteries and electronics provide useful models.
Photovoltaic Cells (Solar Cells) Organic Materials • Pure and chemically modified fullerenes • polythiophene derivatives • polyphenylene vinylene
Organic Materials • Current obstacles • All of the PV cells made from Organic molecules decompose rapidly. • Only 3-6 % conversion of solar energy to electricity
Conclusion • Using a combination of Passive solar energy and photovoltaic cells can lessen pollution. • Concerns with use of Cadmium in PV cells is exaggerated when compared to electricity produced from coal • More research is needed and being done • Cost of Solar system will come down in price when production increases
Sources • http://www.abc.net.au/rn/science/earth/stories/s225110.htm • http://www.solarenergy.com/info_history.html • http://pvpower.com/pvtechs.html • http://www.adsdyes.com/fullerenes.html • http://www.azsolarcenter.com/design/pas-2.htm • http://www.eere.energy.gov/RE/solar_concentrating.html