Batteries for solar power system

Lead-acid batteries are the most common in the solar system, as well as their initial cost is low, and they are easily accessible. There are many different sizes and designs of lead-acid batteries, but the most important attribute is whether they are deep cycle batteries or shallow cycle batteries.

Shallow cycle batteries, such as the type used as starting batteries in automobiles and trucks, are designed to supply large quantities of current for a short time and take slight overcharging. But they are not intended to be deeply discharged and regular discharging will reduce their life and this makes them poor choices for photovoltaic (PV) based solar system.

Deep cycle batteries, which can be repeatedly discharged to 80% of their capacity are a good choice for solar energy systems. They can also be used with shallow-cycles (20% of their power) without reducing their life.

Sealed deep cycle lead-acid battery are maintenance free. They do not require topping up and are ideal for remote power systems. But these benefits come at the price and therefore they are more expensive then the standard batteries.

The size of the battery bank will depend on the storage capacity required, the maximum rate of discharge, the maximum charge rate and the minimum temperature at which the batteries will be used.

In order to determine the total battery amp hours, you must first determine the total number of watt-hours required to load everything and then divide by the nominal voltage DC systems.

This number will indicate the amount of amp hours required for the operation of all loads for a given period. Nevertheless, an additional amp hour capacity, as a rule, will be added to a "reserve" or the capacity to prevent the full discharge.

Battery Wiring

Battery wiring

Series wiring relates to the electrical connection of batteries to increase the volts, not amps. If you have two 6V 300 amp hour batteries and connect the positive terminal of one to the negative terminal of the other you have a combined voltage of 12v, and an additional 300 amp hours (see diagram)

Parallel wiring is when batteries are connected to increase the amps, but not volts. If you have two 12V 300 amp hour batteries and connect the positive terminal of one to the positive terminal of the other you have a combined voltage of 12V, but the 600 amp hours (see diagram).

Charge conversion

The following table allows conversion of the voltage reading with the charge level. The table is accurate for a battery temperature of 77 degrees Fahrenheit. If the temperature is lower, then expect a lower reading.

Charge conversion