November 25, 2012
How Does Solar Energy Work?
Alan McStravick for redOrbit.com - Your Universe Online
The most abundant form of energy ever known has always been there. Through the course of human history, the Sun has offered, without cost, its light and heat for the benefit of every living organism on this rock we call Earth.
If we view solar energy through the prism of time, we see that it is the basis for almost every form of energy that is currently in use. Plants, which we use in the form of biomass, derive their energy and growth potential from the Sun. If those same plants are not immediately used for energy output and are, instead, allowed to rot and compress over millions of years, they will eventually form coal and oil. Wind energy is derived from the Sun, as well. When water evaporates and falls upon higher elevations, the rush down to sea level produces energy that can be manipulated by hydroelectric turbines.
When we think about the enormous reserves of fossil fuels contained just under the surface of the Earth, it is important to recognize that all of those vast resources are matched in energy output by just 20 days of direct sunshine. Above the Earth´s atmosphere, the Sun produces approximately 1,300 watts per square meter. One-third of that energy is reflected back into space. Part of the remaining two-thirds is absorbed by our atmosphere. This absorption by our atmosphere produces our surface winds.
After its trek through both time and space to our planet, the energy that reaches the surface is equal to 1,000 watts per square meter. If that amount of energy is averaged over the entire surface of the planet, it is estimated that every square meter of the earth can produce 4.2 kilowatt-hours of energy each day. However, until our ability to harness this energy is improved we can only expect to capture about one kilowatt-hour of energy each day.
The idea that we could capture and harness energy from the Sun was first realized in 1839 by French scientist Edmund Becquerel. Becquerel discovered that there were certain materials that could produce a spark of electricity when struck by sunlight. These materials were called photovoltaics and primitively were made of selenium. It wasn´t until the 1950´s that researchers from Bell Laboratories made the leap from selenium based photovoltaics to silicon. This advance allowed for a total amount of 4% of the Sun´s energy to be captured. It was only a few years later that this technology was used to power both satellites and space craft.
These photovoltaic cells (PV) typically consist of two layers of a semiconducting material that consists of silicon crystals. By themselves, silicon crystals are not generally a good conductor of electricity. However, through a process called doping, impurities are added to the crystals that help in the production of an electric current. The bottom layer of a PV cell is doped with boron. The boron bonds with the silicon to aid in the production of a positive charge. The top layer is doped with phosphorus, creating a negative charge.
The future of solar power is an ever evolving process that is exploring new materials for its eventual advancement. Higher efficiency materials like gallium arsenide, copper-indium-diselinide and cadmium-telluride are being used to produce amorphous cells that are more sensitive to different parts of the light spectrum. Stacking cells made of these materials allows for the capture of more available light.
As architects and designers are recognizing the cost-benefit of solar power, the growth of this technology is on the cusp of hugely significant growth in this century. Internationally, Germany and Japan have helped to advance solar power by offering aggressive financial incentives for its deployment. The United States, though behind the curve, is working to utilize solar power as a viable energy alternative. As PV technology advances and costs decrease, solar power as an alternative will be more easily achieved. The solar PV industry believes they will provide half of all U.S. electricity generation by the year 2025.