SUN REAL Renewable Energy Systems

About Batteries - Part 1

This is the first part of a series concentrating on the use and abuse of batteries in renewable energy power supplies. Its aim is to give those of you who are using such systems a better understanding of your battery bank and for those of you contemplating using such a system an idea of what you're in for.

The battery bank is a very important part of the power system - it stores the energy generated by the solar panels, wind turbine or micro-hydro and then delivers to you when you need it. The battery bank is also the least understood and often least respected part of the power system. They are much more complex than just a petrol tank that needs to be filled up with fuel when it is empty although that is how they are often treated.

There are several types of batteries available to store energy in a remote area power supply system (RAPS). By far the most common is the flooded lead-acid battery. Others include absorbed glass mat (AGM) lead acid, gel type lead acid and nickel cadmium (NiCad). As the name suggests the flooded cell consists of a liquid electrolyte(diluted sulphuric acid) and a set of basically lead plates. It is the chemical reaction between the sulphuric acid and the lead plates that allows us to charge and discharge a battery. The term "deep cycle" refers to the fact that a battery can be fairly deeply discharged and then re-charged without seriously reducing battery life.

Batteries are rated in terms of their amp-hour capacity and their nominal terminal voltage. So you might have a 12 volt, 100 amp hour battery or a 2 volt 500 amp hour battery. The larger the amp hour capacity the more energy a battery can store. The rate at which a battery is discharged will effect the amp hour capacity so the discharge rate is usually specified along with the amp hour capacity e.g. 500AH @ C10, which means the battery will supply 500 amp hours of energy if discharged over a 10 hour period. The C100 rate is usually used in the design of RAPS systems.

In the next article we look at battery safety and basic maintenance.