Solar electric systems, also known as photovoltaic (PV) systems, convert sunlight into electricity.



The basic building blocks of a PV system, solar cells, 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. 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 basic PV or solar cell typically produces only a small amount of power. To produce more power, solar cells (about 40) can be interconnected to form panels or modules. PV modules range in output from 10 to 300 watts. If more power is needed, several modules can be installed on a building or at ground level in a rack to form a PV array.

PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. Note: Studies have shown that tracking arrays in high intensity sunshine areas like Southern California do not provide enough extra energy to justify the additional installation and maintainance costs of the tracking hardware.

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). Off-grid systems are normally only permitted in remote areas that have no electrical provider.

 
Source: U.S. Department of Energy: A Consumer's Guide to Energy Efficiency and Renewable Energy

In the diagram above, here is the process:

• The solar panels convert the sun's energy into direct current (DC) electricity. DC power is the same as you would receive from a battery.
• The DC power goes through an inverter that converts the DC power into AC electricity, the power used to run your home lighting and appliances.
• When the home is using a lot of power, the inverter feeds this electricity to your home. When the solar cells are producing more power than the home needs, this electricity goes through the meter and is sent back to your utility company (SDG&E in San Diego County).
• When you are sending power back to the utility company, your meter runs backwards, reducing your reading and giving you a credit on your utility bill.
• Existing regulations do not permit you to send more electricity back to the utility company than you use, so you will never get a check from your utility company, but your design consultant will assist you in creating a system that reduces your electric bill to the lowest level possible.