Batteries are an important component of off-grid and many grid-tied residential solar power systems. They are used to store excess electricity produced by the photovoltaic panels for times when they are producing less electricity than needed, such as at night. Batteries are used in both off-grid applications and in grid-tied battery-backed systems. Batteries for off-grid are usually sized to last through normal use on three cloudy days.
The batteries in grid-tied residential solar power systems are used for backup when the grid goes out. There are usually fewer batteries in these banks because they are only used for backup rather than being used every single night.
The three main types of solar batteries are all lead-acid batteries. However, they are very different from the batteries used in a car because they are deep cycle batteries. This means that they can be drained much more deeply of their charge than shallow cycle batteries such as those used in cars. Car batteries will not stand up to the strain that a residential solar power system will place on them.
Batteries Suitable for Residential Solar Power Systems
Flooded Lead-Acid Solar Batteries
Flooded lead-acid batteries are the cheapest type of lead-acid batteries commonly used to store solar power. They also have the longest life, but require regular maintenance. Distilled water must be added as necessary to replace that lost during charging, and because they are not sealed they must be kept clean and there is a danger of spillage.
Absorbed Glass Matt Sealed Lead-Acid Solar Batteries
These are sealed, and therefore do not require regular maintenance as flooded lead-acid batteries do. They are a newer invention and so far less widely used than flooded lead-acid.
Gelled Electrolyte Sealed Lead-Acid Solar Batteries
These are freezing resistant and are typically used in unheated spaces. They must be charged slowly in order to avoid decreasing capacity, making them better for grid-tied backup than for off-grid uses.