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This factsheet provides flow charts for the four most common solar electric system options. Each system is designed based on whether it includes batteries, whether it is connected to the utility grid, and the electrical load. The term “grid” refers to a utility company’s system of transmission and distribution lines that carry and deliver power plant-generated electricity to your home or business. Step 4: System Components factsheet provides information about each major component.
Grid-connected systems are connected to the utility power grid. They are also called grid-tied systems. Grid-connected systems without batteries are currently the most common/popular system type. PV panels produce electricity when the sun is shining during the day. At night, electricity comes from the utility grid. If during the day the building or equipment needs more electricity than the PV panels are producing, electricity is provided by the utility grid. If the PV panels are producing more electricity than needed, the extra electricity is fed into the utility grid. If there is a daytime power outage, the PV system automatically shuts down (does not supply electricity) for utility worker safety.
Grid-connected systems with batteries work exactly the same way as grid-connected systems except electricity is stored in batteries for use during a utility power outage. Homes/buildings can have dedicated “critical” electrical loads powered by the batteries. These loads might include a refrigerator, water- and heat-related pumps, furnace fans, medical equipment, or a computer for a home-based business.
Off-grid systems are not connected to the utility grid. They are also called stand-alone systems. PV-generated electricity is stored and used from batteries. These systems are typically installed in remote areas where connecting to the utility grid costs more than an off-grid system. Off-grid solar electric systems typically have supplemental and back-up power from a small wind turbine and/or a fossil-fueled generator.
PV-direct systems do not entail batteries and are not tied to the utility grid. Thus, they only power the load when the sun shines. They can have moving parts such as pumps. These systems have the fewest components and are used with DC-powered appliances or equipment. Applications include water pumping, building ventilation, etc.
Simple, DC-powered systems can have batteries for applications such as electric fences that need to be powered at night. Whether from the ground or a river, water can be pumped for crops or livestock using photovoltaics.
Morris, Mike, and Vicki Lynne/National Center for Appropriate Technology (NCAT). (2002, October). Solar-Powered Livestock Watering Systems. IP 217. https://attra.ncat.org/attra-pub/solarlswater.html
Sanchez, Justine. (2011, Aug./Sept.). PV Systems Simplified. Home Power, 144, 70-78.
U.S. Dept. of Energy. (2011, Feb.). Equipment Required for Stand-Alone Systems. Retrieved February 16, 2011, from http://www.energysavers.gov/your_home/electricity/index.cfm/mytopic=10620