California Center for Sustainable Energy

Photovoltaics ( PV) literally means "light-electricity," and is the process of converting sunlight into electricity. The term "photo" comes from the Greek word "phos" or light, and "volt" was derived from Volta (1745-1827), a pioneer in the study of electricity.

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How does it work?

When some materials are exposed to sunlight, they release small amounts of electricity giving off what is known as the "photovoltaic effect."

Sunlight is composed of photons, or particles of solar energy that contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, the energy of the photon is transferred to an electron in a cell's atom. The cell is made of a semiconductor material.

With its newfound energy, the electron escapes from its normal position on the atom and becomes part of the current in an electrical circuit. When this happens, the electron creates a "hole." Special electrical properties of the PV cell, specifically a built-in electric field, provide voltage that drives the current through an external load, such as a light bulb, a hairdryer or a television set.

For more information about the science behind PV,
visit the National Center for Photovoltaics.

The components of PV systems

Photovoltaic modules are the basic building blocks of solar electric power systems. PV modules can be made from several different materials, which vary in cost and conversion efficiency. Modules are combined to create panels. Panels are combined to form arrays. Solar electric power systems may also have batteries, charge controllers, and inverters, which convert the direct current generated by PV system into an alternating current, the type of electricity sold by utilities and required to run most appliances and electronic devices.

source: British Photovoltaic Association

Types of Solar Modules

There are two major categories of solar modules, Crystalline and Thin Films. There are a couple types of each and each has its positive and negative factors.

CRYSTALLINE PANELS	THIN FILM PANELS
Types of Crystalline panels Single Crystalline (15%) Multi-Crystalline (14%) (% of sunlight converted to electricity)	Types of Thin Film panels Amorphous Silicon (5-7%) Copper Indium Diselenide (10%) Cadmium Telluride (7%) (% of sunlight converted to electricity)
Positive factors Efficient Requires less space Long track record	Positive factors Less expensive Very versatile More shade tolerant Less temperature sensitive
Negative factors Costly Limited applications Shade intolerant Temperature sensitive	Negative factors Shorter track record Lower efficiency Requires more space

PV systems in use today...

Did you know that PV is part of our daily lives? San Diego's highway call boxes and the I-15 FasTrak^tm signs are PV powered, and many wrist watches and small calculators are too.

If you own a home or business in a remote region of the county, photovoltaics can provide affordable electricity to your residence, water pumps and communications equipment. If you are buying a new home in San Diego, you can get one with a built-in PV system, like the Shea Homes in Scripps Ranch.

For existing San Diego homes and businesses that buy their power from SDG&E, PV is a viable and increasingly attractive method of generating power. Why? PV Systems are now more efficient than ever, and rising electric rates, incentive programs and environmental concerns have compelled many San Diegans to think seriously about buying PV Systems.