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Photovoltaic
Energy |
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| More than 4,000 ft2 of monocrystalline PV panels cover the south-facing roof of the Lewis Center at Oberlin College and are connected to the Ohio power grid. When the PV panels produce more energy than is needed by the Lewis Center, excess power is donated to the local utility, supplanting some coal-fired power production. When the Lewis Center demands more energy than the PV panels can supply, the center purchases power from the utility. |
| History -
The ability of converting solar energy directly to electricity
was first observed by Edmond Becquerel in 1839 but no use was made
of the knowledge. In 1876, William Grylls Adams, professor of Natural
Philosophy at King's College, London and one of his students, Richard
Day discovered that exposing selenium to light produces electricity
and this effect is the basis for the modern solar cell. In 1953,
Calvin Fuller, Gerald Pearson, and Daryl Chapin, discovered the
silicon solar cell which had a high enough efficiency and produced
enough electricity to run small devices. Federal funding was attached
to the space program where solar cells were used to power the Vanguard
satellite. Interest in terrestrial applications of photovoltaic
systems dramatically increased during the 1970’s after the
1973 oil crisis and the National Science Foundation (NSF) organized
a conference at Cherry hills, NJ to lay the foundation for terrestrial
applications of the solar cell. By the late 1970s, a program was
set up at the Massachusetts Institute of technology by the US government
that focused on “design and demonstration issues for the
Business sector” Technology - The most important component of the photovoltaic cell is the semiconductor layer where the electric current is created. Normally a semi-conductor acts as an insulator as there are few free electrons in the conduction band. Most are bound in the valence band and therefore cannot carry a current. However, an external energy source that is greater that the band gap energizes these bound electrons and releases them from the valence band to the conduction band leaving behind positively charged “holes”. A PV cell is designed to focus these released electrons and holes into an electric current. One cell on its own produces a small amount of power, current by voltage; modules are thus created by connecting many cells together. Cells can be added in series, which then increases their voltage, or in parallel which increase their current. In either case the end result in an increase in the power output of the module. Modules can then be connected to form arrays and arrays into systems. There are two types of module systems: flat plate and concentrator with the flat plate system being the simpler of the two. In this system modules are merely built upon a flat surface to capture unconcentrated sunlight and can use both the direct and diffuse components of sunlight. Concentrator systems however use lenses to direct the sunlight on the cells. There are pros and cons to both arrangements. Concentrator systems can focus a large amount of energy and therefore use small area cells to capture the light. This results in much smaller systems and saves on system cost but produces the same amount of power. However unlike the flat-plate system, the concentrator can only use direct sunlight and not diffuse, reducing the amount of time that it is effectively working. For more information of the technology behind Photovoltaics see the National Renewable Energy Laboratory, Solar Research. |
| Photovoltaic Energy | Wind Energy | Geothermal Energy | Hydroelectric Energy |
This page
was created by Alana
Belcon FP'04 in Environmental
Studies 390, |