Storage batteries are the heart of an independent power system. They store
electricity for use at a later time when a charging source (sun, wind, water or
generator) is not available. They also provide a reserve of available energy to
run loads that require more power than that provided by the charging source.
Batteries wear out and must eventually be replaced. Regular monitoring and
maintenance will extend the life span of your battery bank and save you money.
The deeper they are discharged, the shorter their life span will be. Batteries
contain toxic materials and should be disposed of properly.
Choosing a Battery
There are many types of batteries available. Many are unsuitable for an
independent power system. Choosing the right type of battery is the first step
in designing a reliable renewable energy system.
Car batteries are designed to provide a brief, high current for engine
starting, not for deep discharge applications. The 'Cold Cranking Amps' rating
does not indicate the battery's storage capacity. The thin plates in these
batteries are good for a quick release of energy, but deep discharging will
cause rapid deterioration. These are a poor choice for alternative energy
RV and Marine Batteries
These Batteries are a compromise between engine starting batteries and deep
cycle batteries. The plates are similar to the engine starting batteries and
will not withstand repeated deep discharging. They are adequate for small
(under 200 amp / hours) systems and might last 2 to 4 years. These are not a
true deep discharge battery despite the claims on the label to be a 'deep
Motive Power Batteries
Motive batteries are deep-cycle batteries used to provide energy for electric
vehicles such as golf carts and forklifts. They have thick plates that will
withstand many deep discharge cycles. These are used for most independent power
systems as they are durable, have good storage capacity and are cost effective.
These are usually in a 2, 6 or 12V casing. Typically, the golf cart batteries
will last four to seven years, while the Global-Yuasa forklift batteries will
last 10 to 20 years.
Gel (sealed) Batteries
These cells, common known as utility backup cells are used by telephone
companies for back-up power supply systems. They are often designed with
calcium alloy plates which are not for deep cycling, so they are poor batteries
for a most renewable energy systems. However, they may be suitable for use in
systems where there is no requirement for autonomy such as a micro hydro
installation. When batteries are used this way, also referred to as 'float
service', they are storing reserve energy for peak load demands. Stationary 2V
cells frequently come in a clear casing.
Gel cells are filled with an electrolyte that is in the form of a gel or
sponge. It is not possible to service this type of battery or replace the
electrolyte. They have a much shorter life and cost considerably more than
liquid filled batteries. These batteries require no maintenance, tolerate low
temperatures, do not spill and do not produce corrosive gases. They are good at
remote sites where maintenance is not possible and cold weather prevails.
Precise charge control is critical.
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