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Batteries for Solar Power Systems – from MySolarPower

You may find with a PV system that if you are not wishing to be connected to the local grid, then you will need solar batteries to store the solar electricity your solar panels have already generated.

The solar batteries are designed to store the electricity your system has produced which may be used when your system is not generating such as at night or during poor weather cycles.

Solar batteries are very much a key component especially in a stand-alone renewable energy system, and without due care, they can fail and shut the system down. It is not in either case, necessarily the cheapest or the most expensive batteries that will best suit your requirements, so always speak to your system supplier before purchasing solar battery systems. Most solar energy systems are demanding applications for the battery so to maintain the system integrity it is important to select the most effective battery for your system.

 What are batteries?

A battery is, in simple terms, a device for the storage of energy for use at a later date.

A battery itself however only stores and subsequently distributes energy, it does not generate any and, will require this energy to be replaced once used otherwise it will be of little or no use.

Probably the most frequently used batteries for solar applications are deep cycle batteries. The most common being the Lead acid format because they are less expensive than some others and pretty reliable – however they do damage easily so need to be handled with care with no over-charging and not over discharged. The most common are AGM batteries or GEL batteries, where little or no user maintenance is required.

Batteries for the solar energy systems may come in tubular and flat plate designs.

Deep Cycle Batteries

Because it is damaging to over-charge or over-discharge the lead acid deep cycle batteries deep cycle batteries have far heavier and stronger lead plates inside of them than those found in ordinary lead acid batteries.

Both GEL and AGM (Absorbed Glass Matt) batteries store charge well and don’t deteriorate as quickly as the common lead acid (wet cell) battery. Because of the type of material used as the electrolyte (GEL or Absorbed Glass Matt) there is little chance of a hydrogen gas build up that can lead to an explosion and these batteries are not subject to corrosion. As a matter of cost, AGM batteries are normally less expensive than GEL.

Leisure batteries and marine batteries are generally a cross between a starting battery and a deep cycle battery. They are cheaper than true deep cycle batteries due to the fact that they use less lead in their construction.

The life of a battery is expressed as 'design life' or 'cyclic life'. If a battery is not cycled much, it will normally last for the design life. If a battery is cycled regularly, its life will depend on the depth of the discharge cycle and the number of cycles it has to do. This data is often shown plotted on a graph by the manufacturers and is the key to a good deep cycle battery.

What level of battery storage is required?

The standard calculation would seem to be around 5 times your average daily usage.  To work out what you storage you require just calculate your average daily usage in watts and divide by the battery voltage. For example, if you use 3 KWh (Kilowatt-hours) or 3000 Watts of electricity per day and your solar electricity system operates at 12 volts, then dividing 3000W by 12V gives you 250 AH. It’s important that the battery is not discharged and we suggest discharge should not be more than 50%. At 50% discharge you will need 500AH of battery storage. 

AGM solar Batteries – so called because they use “absorbed glass mats” between the plates – they are pretty robust and low maintenance. They are sealed so can not be spilled, so they don’t need topping up with distilled water (like car batteries) and don’t emit corrosive fumes – they don’t discharge themselves easily so are well suited to systems that are subject to infrequent use.

GEL solar batteries – this is where the acid has been turned into a solid state, which means that even if broken, the can not spill. Albeit not usually a problem with solar electric systems it should be noted that they can’t be fast charged as it may result in permanent solar battery damage.

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