Basics of Grid-Tied PV

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Most residential photovoltaic (PV) systems consist of PV modules, a battery bank to store the electricity, a charge controller to regulate the charging of the batteries, and an inverter to change the solar-generated direct current electricity into the more commonly used alternating current. People living in remote areas of the U.S., off the grid, have been relying on these types of PV systems for years. However, more and more people who are already connected to the grid are turning to renewable energy for part or all of their electricity needs. These grid-tied PV systems send solar-generated electricity back into the already existing utility grid.

With a grid-tied system there is no battery bank - the utility company acts as the battery. (Many people choose to keep batteries, however, as a backup in case of grid failure.) When a system produces more electricity than is needed, the excess is sold to the utility company. When the homeowner needs more electricity than is being produced, electricity is bought from the utility company. Under federal law, the Public Utility Regulatory Policy Act (PURPA, Section 210), utility companies are required to buy electricity from renewable energy producers.

The other difference in grid-tied systems is the type of inverter used. Line-tied inverters are designed to sense the presence of grid power and shut off when the grid does. This keeps the PV-generated electricity off the grid in case there are utility people working on it.

The majority of grid-tied PV systems use PV modules mounted on a roof or a pole near the house. However, some systems use PV cells that actually become an integrated part of the building (a common example are PV roof tiles). While these systems may reduce the cost of PV systems, they are still about 50% more expensive than standard PV modules. And standard PV modules don't come cheap.

For more information:

Solar Energy International ,
P.O. Box 715, Carbondale, CO 81623; (970) 963-8855;
fax: (970) 963-8866;
e-mail: sei@solarenergy.org ; Web site:
www.solarenergy.org

Solar Sales & Service ,
White Bluff, TN 37187; (800) 398-5188 or (615) 8761911;
e-mail: SOLARSALES@aol.com

Sacramento Municipal Utility District , P.O. Box 15830, Sacramento, CA 95852-1830; www.smud.org

Home Power Magazine,
P.O. Box 520,
Ashland, OR 97520;
e-mail: hp@homepower.com ;
Web site: www.homepower.com

1 Maka Rukus and Jenny Freely, "Guerrilla Solar." Home Power Magazine, Issue #67, October/ November 1998, page 35.