Solar Panels: Harvesting the Energy from our Sun


irtually unlimited power is available from our nearest star, the Sun. In just one hour, our planet receives more energy from the sun than the entire world uses during an entire year. Electricity-pro- ducing solar panels have only been around for the last 60 years, yet they have complete- ly transformed how we harness solar energy. In 1839, a nineteen year-old French


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physicist named Alexandre-Edmond Bec- querel discovered the operating principle of the solar cell, known as the photovol- taic effect. It wasn’t until 1876 that this effect materialized into a viable method of producing electricity, through the work of William Grylls Adams. He discovered that by illuminating a junction between selenium and platinum, a photovoltaic effect occurs; electricity could now be produced without moving parts. Revolutionary as they may have been, the selenium solar cells were not efficient enough to power electrical equipment. That ability occurred in 1953 when a Bell Laboratories employee, Gerald Pearson, had the bright idea of making a solar cell with silicon instead of selenium. The New York Times heralded the discovery as “The begin- ning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.” Just in time for the space race, the first solar panels made their debut in the satellite industry. Vanguard I, the first solar-powered satellite, celebrated its 53rd birthday this year, setting mileage records and holding the title of being the oldest artificial satellite still in orbit.


Whereas the first solar modules were only efficient enough for space applica-


14 Natural Nutmeg March 2012


tions, the Sun’s radiation is much stronger. Eventually, satellite research paved the way for Earth-based technology. The 1990s were pivotal years for photovoltaic technology. Innovations in solar cells allowed for greater efficiency while lowering the cost of produc- tion. Germany and Japan led the way with long-term solar power incentive programs, helping lower the cost to the public, and spurring the growth of a robust photovoltaic industry in both countries.


California Leads the Nation


In 2006, California, made a major commitment to solar power by passing the California Solar Initiative, a ten-year incen- tive program with the goal of installing 3000 megawatts of solar panels on the equivalent of one million rooftops. California leads the nation in solar panel installations. This incredible boom has taken place mostly due to California’s Renewable Portfolio Standard, which required that 20 percent of the state’s electricity come from renewable resources by 2010. In 2008 the state decided that it was not moving fast enough to meet these goals and enacted a feed-in tariff, requir- ing utility companies to buy back excess power produced by homeowners and private photovoltaic installations. That same year the state also increased the Renewable Portfo- lio Standard to 33 percent by 2020, greatly helping spur growth in the renewable energy industry.


How Solar Panels work


Photovoltaic solar modules are com- posed of multiple, interconnected solar


cells, which effectively trap photon energy between layers of silicon wafers. Negatively charged electrons are then knocked loose from their atoms, allowing them to flow freely through the semiconductors. Separate diodes and P-N junctions prevent reverse currents and reduce loss of power on par- tially shaded panels. Since the flow of electrical current is going in one direction, like a battery, the electricity generated is called Direct Current (DC). Sunlight conversion rates are typically in the 5 to 18 percent range, with some laboratory experiments reaching efficiencies as high as 30 percent. Future possibilities include the development of multi-junction solar cells that are capable of harnessing a wider bandwidth of useable light. We are still considered to be in the “early” stages of solar cell technology.


Solar Panel Components Photovoltaic solar panels are the main


building block in a solar power system. Since each solar module produces a limited amount of power, installations usually con- sist of multiple panels, called an array. The array produces DC, which can be stored in batteries or instantly converted into AC (Al- ternating Current) required by conventional appliances. The equipment that converts power from


DC to AC is known as a solar inverter. Solar inverters come in a few varieties; they can be modified sine wave or pure sine wave and are further classified based on the type of system they will be used in, whether it is off-grid or grid interconnected. Recently, the innovation of micro inverters has greatly


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