How Solar Energy Works
Solar energy, radiant light and heat from the Sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.
Solar PV (Panel) Systems
Solar photovoltaic (PV) systems change sunlight directly to electricity using solar cells. Solar cells are small, square-shaped panel semiconductors made from silicon and other conductive materials. They are manufactured in thin film layers. When sunlight strikes a solar cell, chemical reactions release electrons, generating electric current. Solar cells can be found on many small appliances, like calculators. Individual PV cells are arranged together in a PV module and the modules are grouped together in an array. Some of the arrays are set on special tracking devices to follow sunlight all day long.
The electrical energy from solar cells can then be used directly. It can be used in a home for lights and appliances. It can be used in a business. Solar energy can be stored in batteries to light a roadside billboard at night. Or the energy can be stored in a battery for an emergency roadside cellular telephone when no telephone wires are around.
Solar Hot Water Heaters
In the 1890s solar water heaters were being used all over the United States. They proved to be a big improvement over wood and coal-burning stoves. However by 1920, large deposits of oil and natural gas were discovered in the western United States. As these low cost fuels became available, solar water systems began to be replaced with heaters burning fossil fuels. Today, solar water heaters are making a comeback.
These systems heat water for use inside homes and businesses. They also heat swimming pools. Panels on the roof of a building contain water pipes. When the sun hits the panels and the pipes, the heat of sunlight warms them.
At any time of the day, a customer's renewable energy system may produce more or less electricity than their home or business needs. When "excess" electricity is produced by the system, it will automatically go through the electric meter into the utility grid to be supplied to other customers. When this occurs the meter runs backwards. At other times of the day, the customer's electric demand may be higher than the renewable energy system is producing, and the customer relies on the additional power needs from the utility.
Net energy metering is a special billing arrangement for customers with solar PV systems that permits customers to get credit for the full retail value of the electricity their system generates. Under net energy metering, the customer's electric meter keeps track of how much excess electricity is generated by the renewable energy system and sent back into the electric grid, and how much electricity is consumed by the customer. Over a 12 month period, the customer has to pay only for the net amount of electricity they use from SDG&E over-and-above the amount of electricity generated by their renewable energy system.