Stand Alone Photovoltaic (PV) Systems: A Description & Function of System Components

Solar photovoltaic (PV) energy systems provide electrical energy from the sun. The simplest systems match a solar PV cell or module to a direct current (DC) load such as a water pump or a ventilation fan. These electrical loads operate when the sun is shining. To operate an electrical load such as a direct current (DC) light during evening hours requires an energy storage device such as a battery. A flashlight is an example of a direct current (DC) load (lamp) operating on batteries. The lamp will shine if the batteries produce a charge. When the batteries lose their energy, the lamp begins to fade and will eventually cease to shine. A solar cell connected to the batteries of the flashlight could re-charge the batteries during daylight, so energy is once again provided to the lamp. For the circuit to operate, the size of the cell must match the size of the battery. Larger electrical systems with voltages higher than 1.5-volt batteries require a component to regulate the flow of electric current from the PV module to the battery and monitor the state of charge (SOC) of the battery and protect the battery from being drained by the electrical load. Examples of solar PV circuits with batteries include solar-charged calculators, wrist watches, flashlights, and lanterns. Our garden pathway lights are solar-powered as well as wall-mounted outdoor spotlights. They are simpler to install because they are not wired to our house circuits and are gaining popularity with homeowners. This publication is intended to guide homeowners with an interest in stand-alone solar PV systems.