U.S. Department of Energy - Energy Efficiency and Renewable Energy

Solar Energy Technologies Program

PV Systems with Generators

This PV-hybrid system (PV and an air-cooled propane generator) at the Miner Institute in Chazy, New York, provides electricity for a variety of instruments at an environmental research facility, which monitors the effect of environmental changes on atmospheric carbon released from temperate forest and wetland soils. The project was developed by the New York State Energy Research and Development Authority and is partners.

What about situations in which remote or non-grid-connected power is needed, but that power must always be available — for example, to keep vaccines cold, or a rural clinic's lights on, or communications equipment running continuously? Or the times when users know they'll occasionally need a larger amount of power than a PV system can supply alone — say, in a national park camping ground, where it's difficult to predict how much power will be needed? In those cases, PV is still a practical choice. We just need to add an electric generator that can work effectively with a PV system to supply the load.

During the day, the PV modules quietly supply daytime energy needs and charge batteries. If the batteries run low, the engine generator runs at full power — its most cost-and fuel-efficient mode of operation — until the batteries are charged. And, in some systems, the generator makes up the difference when electrical demand exceeds the combined output of the PV modules and the batteries. See our case study on a telephone signal booster for a good example of such a remote application.

Systems that use several types of power generation have the advantages of each one. Engine generators can produce electricity any time. So, they provide an excellent backup at night or on cloudy days for the PV modules, which produce power only during daylight hours. The advantages of a PV system are that it operates quietly and does not pollute. As to the rather high initial cost, we can select a smaller PV system if we operate it with a generator.

Where no other form of power generation is available, the PV array and the battery storage have to be large enough to supply nighttime electrical needs. However, having an engine generator as a backup means fewer PV modules and batteries will be necessary to supply power whenever it's needed.

Including a generator makes designing a PV system more complex, but it's still easy to operate. In fact, modern electronic controllers allow these kinds of systems to operate automatically. Controllers can be set to automatically switch generators, to supply AC or DC loads, or to do some of each. Wind generators, small hydro plants, and any other source of electrical energy could also be added to make an even larger hybrid power system.