Battery Capacity
 

What you need to know

What is Battery Capacity?

Battery capacity is determined by the amount of electrical energy the battery can deliver over a certain period of time and is measured in Ampere hours (Ah) when discharged at a uniform rate over a given period of time. Ampere hours (Ah) are calculated by multiplying the current (in amperes) by time (in hours) the current is drawn.

Amp-hour rating is commonly used on sealed lead acid batteries used in Wind and Solar systems.

For example: A battery which delivers 1 ampere for 20 hours would have a 20 amp-hour battery
rating (1 * 20 = 20).

Charging and Discharging Batteries

When a battery is discharged and then recharged it is said to have completed a battery cycle.

For example, if the battery is in a fully charged state and a load is applied (the battery is used) then the battery will start to discharge, some, if not all, of its charge. When it is recharged to its full state it completes one battery cycle. This is important because battery life is determined by the number of cycles a battery can yield and thus the application and use of a battery can be determined.

Selecting a Battery

The choice of battery for any solar PV system depends on many factors.

Follow the rule of thumb.  If fewer than five (< 5 days) of storage capacity is required then deep-discharge batteries are used.  If more than five ( > 5 days) of storage capacity is required then shallow-discharge batteries are used. Why?

Fewer than five (< 5 days) of storage capacity usually means that the batteries are designed to discharge on a daily basis, whereas a battery bank designed for an occasional period of no sun will be sized large enough to require only a shallow level of discharge on a normal, daily basis.

This does not mean that deep-discharge batteries cannot be used in shallow-discharge applications. Of course they can.  When deep-discharge batteries are used in shallow-discharge applications, the service life can be extended considerably. Another factor, perhaps the most important, is the cost difference.  Whatever type of battery is used, care must always be taken prevent electrolyte stratification by frequent cycling, usually performed by a short period of overcharging - the equalising charge.

Another critical factor in battery selection is the location of the solar PV array. If the site is remote and unattended, then maintenance-free batteries should be used. Batteries are very heavy, so sites that are remote will be better served by a larger number of smaller batteries than by a few large batteries.

Connecting Batteries In Series or Parallel

How many batteries can be connected together in Series or Parallel combination?

It's all a question of reliability.

Some manufacturers agree that increasing the number of parallel connections in a battery bank will not reduce reliability; on the other hand, other manufacturers have stated that the number of series-connected batteries can reduce reliability.

Battery Regulation

Batteries need to be properly regulated and our battery regulators are superb.

Overcharging a battery raises its temperature, more specifically; it raises the temperature of the battery electrolyte, causing gassing, loss of still water and damage to the battery plates.

Obviously proper battery charge regulators are essential with battery charging system to limit charging current as the battery voltage rises.

Charge regulators are also useful in keeping a battery close to its fully charged rate as possible, thus ensuring maximum efficiency.

Connecting Batteries together

Series Connection: batteries may be connected together in series. (+ Battery 1 -,?+ Battery 2 -) The positive (+) terminal of the first battery is connected to the negative (-) terminal of the second battery, the positive terminal of the second is connected to the negative of the third, etc. The total voltage of the final battery is the sum of the voltages of the individual batteries. The capacity of the battery is unchanged.

Parallel Connection: batteries may be connected together in parallel.

(+ Battery 1 - )
(+ Battery 2 - )
(+ Battery 3 - )

The positive (+) terminal of the first battery is connected to the positive (+) terminal of the second battery, the positive (+) terminal of the second is connected to the positive of the third and so on.

Also the negative (-) terminal of the first battery is connected to the negative (-) terminal of the second battery, the negative (-) terminal of the second is connected to the negative (-) of the third and so on.

Read our BATTERY SIZING information