Many renewable energy systems that are not connected to the power grid have some method of storing energy. Energy storage allows a system to operate even when there is no input or when the input is not capable of meeting all of the demands of the loads.
Batteries Most stand-alone systems use rechargeable batteries for energy storage.
Batteries used with RE systems are often deep cycle batteries, meaning they can discharge a significant amount of the energy they store before requiring recharging. Some systems also use cheaper shallow cycle models. A lead-acid battery. Courtesy of Solar Energy International . The frequency and depth of energy discharge from a battery has a significant impact on how long it lasts.