A small solar electric or photovoltaic system can be a reliable and pollution-free producer of electricity for your home or office.
A small solar electric or photovoltaic (PV) system can be a reliable and pollution-free producer of electricity for your home or office. Small PV systems also provide a cost-effective power supply in locations where it is expensive or impossible to send electricity through conventional power lines.
Because PV technologies use both direct and scattered sunlight to create electricity, the solar resource across the United States is ample for home solar electric systems. However, the amount of power generated by a solar system at a particular site depends on how much of the sun's energy reaches it. Thus, PV systems, like all solar technologies, function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.
Because of their modularity, PV systems can be designed to meet any electrical requirement, no matter how large or how small. You can connect them to an electric distribution system (grid-connected), or they can stand alone (off-grid). You can also use PV technology to provide outdoor lighting.
See our other pages for more information on planning a home solar electric system and installing and maintaining a home solar electric system.
Types of Solar Cells
Solar cells—the basic building blocks of a PV system -- consist of semiconductor materials. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms. This phenomenon is called the "photoelectric effect." These free electrons then travel into a circuit built into the solar cell to form electrical current. Our Solar Power Basics animation shows a simulation of the photoelectric effect. Only sunlight of certain wavelengths will work efficiently to create electricity. PV systems can still produce electricity on cloudy days, but not as much as on a sunny day.
The performance of a solar (or PV) cell is measured in terms of its efficiency at converting sunlight into electricity. There are a variety of solar cell materials available, which vary in conversion efficiency.
Semiconductor Materials
Silicon remains the most popular material for solar cells, including these types:
Monocrystalline ( for example: GOAL ZERO NOMAD 7 PLUS ) or single crystal silicon
Multicrystalline silicon
Polycrystalline silicon
Amorphous silicon.
The absorption coefficient of a material indicates how far light with a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed.
The bandgap of a semiconductor material is an amount of energy. Specifically, the bandgap is the minimum energy needed to move an electron from its bound state within an atom to a free state. This free state is where the electron can be involved in conduction. The lower energy level of a semiconductor is called the "valence band." The higher energy level where an electron is free to roam is called the "conduction band." The bandgap (often symbolized by Eg) is the energy difference between the conduction band and valence band.
Solar cell material has an abrupt edge in its absorption coefficient; because light with energy below the material's bandgap cannot free an electron, it isn't absorbed.
Thin Film
Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Thin film technology has made it possible for solar cells to now double as these materials:
Rooftop or solar shingles
Roof tiles
Building facades
Glazing for skylights or atria.
Thin-film rooftop or solar shingles, made with various non-crystalline materials, are just now starting to enter the residential market. The following are benefits of these solar shingles:
Attractive integration into homes
Dual purpose -- serves as both roofing material and pollution-free electricity producer
Durability.
Current issues with commercially available solar shingles include their lower efficiencies and greater expense compared with the standard home solar electric system.