1. What is photovoltaics?

Photovoltaic (fo-to-vol-ta-ik) systems are solar systems that produce electricity directly from sunlight. The term "photo" comes from the Greek "phos," meaning light. "Voltaic" is named for Alessandro Volta (1745-1827), a pioneer in the study of electricity for whom the term "volt" was named. Photovoltaics, then, means "light electricity." Photovoltaic systems produce clean, reliable electricity without consuming any fossil fuels. They are being used in a wide variety of applications, from providing power for watches, highway signs, and space stations, to providing for a household's electrical needs.

2. What is the difference between "solar energy" and "photovoltaics?"

Photovoltaics is one form of solar energy. The term solar energy can refer to something as simple the energy gathered in your parked, sealed car (your solar collector) and converted into heat. Solar energy is often used to heat houses directly through passive means (sun enters window, room warms). Solar energy is also often used to heat water (a solar collector is mounted in direct sunlight, which warms a heat transfer fluid, which in turn heats the water in your hot water tank).

Photovoltaics refers specifically to the practice of converting the sun's energy directly into electricity using photovoltaic cells. Photovoltaic cells are often referred to as PV cells or solar cells.

3. What is solar thermal energy?

Solar thermal energy refers to harnessing the sun's light to produce heat. Heat results when photons, packets of light energy, strike the atoms composing a substance (water, your body, asphalt), exciting them. Solar thermal technologies include passive solar systems for heating (or cooling!) buildings; flat plate solar collectors, often used for providing households with hot water; and solar concentrator power systems. These systems, also known as solar thermal power plants, use the sun's heat to create steam, which then turns a turbine and produces electricity. (Fossil fuel burning power plants also produce electricity by first creating steam in order to turn a turbine.)

4. Can I heat my house with photovoltaics?

Using electricity to heat a house, as anyone who uses electric heat and pays monthly bills to the utility knows, is very inefficient and costly. Theoretically, one could heat one's home with photovoltaics (electricity is electricity, whether it comes from PV panels or from a coal burning power plant). Practically, though, this would be costly, as producing electricity from a PV system is more expensive than purchasing it from the utility. One can, however, heat one's house very effectively and cheaply by harnessing the sun's energy in other ways.

5. What are the components of a PV system?

  • Photovoltaic Cell -- Thin squares, discs, or films of semiconductor material that generate voltage and current when exposed to sunlight.
  • Module -- Photovoltaic cells wired together and laminated between a clear superstrate (glazing) and encapsulating substrate.
  • Array -- One or more modules with mounting hardware and wired together at a specific voltage.
  • Controller -- Power conditioning equipment to regulate battery voltage.

6. How do the panels work?

A solar panel (module) is made up a number of solar cells. Solar cells are generally made from thin wafers of silicon, the second most abundant substance on earth, the same substance that makes up sand. To make the wafers, the silicon is heated to extreme temperatures, and chemicals, usually boron and phosphorous, are added. The addition of these chemicals makes the silicon atoms unstable (their electrons less tightly held). When photons of sunlight hit a solar panel, some are absorbed into the solar cells, where their energy knocks loose some of the modified silicon's electrons. These loose electrons are forced by electric fields in the PV panel to flow along wires that have been placed within the cells. This flow of electrons through the wires is electricity, and will provide power for whatever load we attach (a calculator, a light bulb, a satellite, etc.)

Because solar cells are modular, a system's size can be increased (or decreased) over time, according to need.

For more details on the workings of solar cells, check out the following web sites:

7. What if I want electricity at night or on cloudy days?

Introducing batteries to a PV system allows electricity to be stored when the sun is shining. This electricity can then be used to provide power after the sun goes down.

8. How many PV panels do I need for my house?

This depends on how much electricity you use in your home, In a sunny climate, a 2 kilowatt PV system can produce 300 kilowatt-hours of electricity per month. the first step in planning a solar system is reducing electricity consumption. It is always more cost-effective to invest in energy efficiency than to install a larger PV system. Planning, mindfulness and some initial investment can result in a dramatic reduction in electricity use, without sacrificing the comforts to which we've become accustomed. You don't have to sit in a dark, cold room to save energy!