One of the other important elements of a home photovoltaic system is a charge controller. This device prevents your solar panels from overcharging your battery, by keeping the batteries from taking on more current when they're fully charged. Not doing this can cause battery overloads, which, in extreme cases, can be a risk for fire or even an explosion. Very advanced systems, in conjunction with net usage monitoring, can redirect excess power beyond the storage subsystem back to your main electrical grid, where it will be counted as a credit on your bill by your utility company.
Your solar array setup will include a recommended size for a charge controller, the two limits are how much battery capacity you have, and how much current you can expect your array to produce at peak times. Like battery arrays, the most common charge controllers are in 12, 24 and 48 volt arrangements, with more variation in amperage, from 1 amp to 100 amps.
Like sizing your battery array, sizing your controller for a bit overage improves safety, and saves money in the long run. A safe metric is about 25%;if you have four 12 volt arrays rated at 4 amps, getting a 20 amp controller (4x4*1.25) is a safe margin, and gives you options to add more panels down the road.
Other than protecting your batteries from over charging, there are several other features that can be included in your controller. These include: