How do Photovoltaics Work?
A Photovoltaic cell (PV), otherwise known as a solar cell, is use to generate electric power from the sun's radient energy using a phenomena known as the photoelectric effect. The photoelectric effect refers to a phenomena where photons of light knock off electrons into a higher state of energy and these electrons can then be utilized to create electricity. The photoelectric effect was discovered by Alexandre-Edmond Becquerel who found that that certain materials release electrons when hit with light or photons. The first solar cell was constructed by Charles Fritt in the 1880s. A photovoltaic cell is essentially a photodiode in which the current through the device is entirely generated due to the incident light energy. All photovoltaic devices are a photodiode of some type. For a good explanation of how a solar cell works, watch this video:
Solar cells produce DC (Direct Current) electricity from the suns radiation, which can be used as a power source for equipment or to recharge a battery. One of the first, and most practical applications of photovoltaics is to power orbiting satellites and other spacecraft where it is almost impossible to renew any other type of energy supply. However, as photovoltaics have become more commonplace, the majority of photovoltaic modules are used for utility power generation. Because the utilities deal in AC (Alternating Current), an inverter is required to convert the power generated from a photvoltaic from DC to AC. There is also a smaller market for non-grid power for remote homes, shelters, electric cars, remote sensing, street lights, boats, recreational vehicles, roadside emergency cellular phone towers, telephones, etc.
The common measurement for the power emitted by the sun is called solar irradiance. It is measured in watts per square meter. Note that this is for a horizontal surface measured orthogonal to the suns location. Cells require protection and isolation from the environment and are usually packaged on a panel behind a more sturdy glass sheet that is more resiliant to the elements. Since a single cell is typically inadaquate to deliver enough required power, many cells are typically connected electrically to form photovoltaic modules, or solar panels. For example, a single solar panel is enough to power an emergency telephone. However, to generate enough power for a house or a power plant the modules must be arranged in many large arrays. The price of solar panels is still too high to compete with coal-powered electricity in most places, however, significant financial incentives are common some countries including Japan, Germany, Italy, France, and Spain which, in 2008, installed 45% of all photovoltaics, but a change in law limiting the feed-in tariff is expected to cause a large drop in the rate of new installations there, from an extra 2500 MW in 2008 to an expected additional 375 MW in 2009.
A significant market has developed in off grid locations for solar power along with a battery storage solution. These often provide the only electricity available in a remote area. In 2007, world solar photovoltaic (PV) installations were 2.826 gigawatts peak (GWp) , and 5.95 GWp in 2008, a 110% increase. The three leading countries using PV (Germany, Japan and the US) represent nearly 89% of the total worldwide PV installed capacity. An estimated PV worldwide installation outlook for 2012 is 18.8GW
In 2006 and 2007, Germany was the fastest growing photovoltaic market in the world. In 2008, 5.337 GWp of PV was installed which represented 35% of the world's total. The German Photovoltaic industry generates over 10k jobs in production, distribution and installation. By the end of 2006, nearly 88% of all solar photovoltaic installations in the Eur were in grid-tied applications in Germany. Photovoltaic power capacity is measured as maximum power output in "Wp" (Watts peak). The actual power output at a particular point in time may be less than or greater than this value, depending on weather conditions, time of day, location, and other factors and can change the effective usable power is typically 20 to 25% of the peak.. For example, the 2008 installed base peak output would have provided an average output of 3.04 GW (assuming 20% × 15,200 MWp). This was 0.15% of global demand at the time.
In some estimates, by the year 2030 PV systems could be generating up to 1,864 GW of electricity around the world. This means that, assuming a serious commitment is made to energy efficiency, enough solar power could be produced globally in in 20 years’ time to satisfy the electricity needs of almost 14% of the world’s population.
