Photovoltaic solar panels produce electricity whenever the sun shines on them. Stand alone (off-grid) and battery backup grid connected PV systems require a single battery or a group of Deep Cycle Batteries called a “battery bank” wired together to store the generated solar energy.
The photovoltaics charge these deep cycle batteries during the daylight hours so that you can have electricity at night or on cloudy days. Then storage batteries are an essential part of any stand alone or grid-tied alternative energy installation and which themselves can determine the DC operating voltage of the whole photovoltaic solar system. Deep Cycle Batteries consist of a collection of individual smaller 2-volt cells which store the electrical energy produced by the PV panels that are not immediately consumed by the load. Battery cells allow this electrical energy to be converted into chemical energy, stored within the cell, which is then converted back into electrical energy as needed. A battery consists of one or more of these cells, electrically connected together in series or parallel, or both, depending on the required output voltage and amperage.
Then we can define a battery for use in a solar power system as a collection of cells which store electrical energy in the form of chemical reactions.
In the world of batteries, Deep Cycle Batteries are classed as “secondary batteries” because they can be continuously charged-up and discharged producing what is know as the batteries charging cycle. Deep cycle batteries are called secondary batteries because the chemical reaction that produces and stores the electrical energy on its lead plates is fully reversible, as opposed to standard “primary batteries” that can only be used once and then thrown away once they are fully discharged.
In other words, primary batteries such as those small alkaline power batteries used in remote controls or cameras can only be discharged or used once and are then discarded (thrown away) polluting the environment, while secondary batteries called “rechargeables” such as NiCad or Lithium Ion batteries used in laptops etc, can be discharged and recharged many times over and are therefore much kinder to the environment.
But not all secondary batteries are the same, there are many different types of batteries available, with each type designed for a specific applications. Although similar to ordinary car batteries, deep cycle batteries used in solar power systems are especially designed for the type of charging and discharging cycles they need to endure.
The most common type of batteries used in solar PV applications are maintenance free “lead acid batteries” as this type of battery is the most cost effective for home energy storage.