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The Use of Batteries for Storing Solar Power

Batteries for Storing your Solar Power

As your electical power usually needs to be available when the sun is not shining, it usually neccessary to store electricity.

A typical battery pack

The normal storage is the Lead-Acid battery.

This is a good point for some warnings:
1. Lead Acid Batteries can contain a large amount of electrical energy which they are capable of discharging very quickly if any form of conductor is placed accros their terminals.
2. Lead acid batteris contain Sulpuric Acid which is corrosive.
3. Lead Acid batteries give off hydrogen when they are being charged, which when mixed with air is explosive, and can be ignited by a small spark.

For the above reasons, I would not do any work on the batteries (ie changing connections) unless I was wearing goggles to protect the eyes. I would also ensure that the batteries have not been charged during the last 2-3 hours to reduce the risk of hydrogen being present.

A Lead Acid cell has a nominal voltage of around 2 volts (depending on it's state of charge). A battery will consist of severel cells connected together in series to produce the required valtage, usually either 12, 24, or 48 volts.
For a small system, a 12 volt car or truck battery (consisting of 6 cells as one unit) could be used though they are not designed for the job.

The photograph to the right shows a battery of 12 individual cells for a 24 volt system. These cells will have been designed for deep cycle use.

What is a deep cycle cell? Deep cycle refers to the fact that in a solar power system, it is likely that the battery will become charged during a sunny day, then they may become almost fully discharged with use, before they are again fully charged.
On the other hand, a car or truck battery is not designed for this type of use. Although the starter motor of the vehicle will draw a considderable amount of current from the battery, it will nowhere near fully discharge it (unless the vehicle fails to start and the driver continues using the starter motor for some time). The car or truck battery is therefor designed to be used virtually fully charged all of the time.

Although a car or truck battery may be used for a small solar power system, it may only have a life of 2 to 3 years if used continously, compared to 10 to 15 years for a deep cycle battery.
However in a small solar power system where power is not required every day and the batteries are therefor fully charged most of the time (in a weekend lodge for instance) a car or truck battery will have a more reasonable life expectancy.