THE BATTERY BANK
In order to use the energy that you harvest whenever you want, from the source of power that you choose, you need an energy storage system. That is, you need a battery bank.
Four kinds of batteries are most commonly used:
Wet
lead acid
Wet Lead Acid batteries are the most common batteries used in renewable
energy systems because of their price, local availability, and ease of
recycling. A properly maintained lead acid cell will last about ten years.
This type of battery will deliver about 1,000 full charge-discharge cycles.
Its drawbacks include the following:
• the batteries need to be equalized every month or so
• the water needs to be replenished often
• the batteries corrode and contacts need to be cleaned frequently
• the batteries are not freeze-tolerant and they need to be in a
warm environment or need to be insulated
• the batteries release gases while charging so they need to have
an exhaust to the outside.
Gel
cell
These batteries are also lead acid but the electrolyte is in gelatin form
instead of liquid. Thus, they need no maintenance: water does not
need to be added, and it doesn't corrode. They can also be stored in any
position and since there are no dangerous fumes, they can be placed in
any part of the house. It will not freeze (when fully charged, it can
function in -30C or -20F). These batteries are ideal for part-time dwellings
where they can be left unattended for long periods of time. Its drawbacks
include the following:
• this type of battery will deliver only about 200-500 full charge-discharge
cycles
• they are three times more expensive than wet lead acid batteries
• in a well-maintained system, life expectancy is shorter than that
of wet lead acid batteries.
AGM SunExtender
Series
Similar to the Gel cell batteries. But instead of having an electrolyte
in a gelatin form, the electrolyte is absorbed into a very fine glass
mat and is never free to slush around. The absorber glass mat (AGM) separator
provides ideal wicking characteristics for electrolyte retention.
These batteries are
sealed, so they can be placed in any position. They also do not need watering,
they don’t produce any gas, and they do not corrode; therefore, they
are maintenance free. AGM batteries have an extremely low electrical resistance,
and they deliver much higher power efficiency than gel cell and wet lead
acid batteries. They have higher full charge-discharge cycles than gel
cell batteries, and can tolerate overcharge. These batteries perform very
well in extreme temperature conditions and have a very low rate of self-discharge.
They are UL listed, which will please the electrical inspectors and insurance
companies.
The drawback:
- The price, which is almost the same as the gel cell.
These are the best batteries you can buy for stand-alone or backup systems.
Ni-Cad
These are one of the best batteries available. They are not prone to corrosion.
They are not damaged by freezing. They have higher charging and storage
efficiency at temperature extremes than lead acid batteries. They are
more resistant to over-discharge and over-charge than lead acid batteries.
The maximum lifetime for a properly maintained nickel cadmium cell can
be as long as fifty years. Average life expectancy is around twenty to
twenty-five years. There is no need to equalize them. Nicad will deliver
about 2,000 full charge-discharge cycles. Its drawbacks include:
• price! These batteries cost between six to ten times the amount
of a similar capacity lead acid pack.
• they are difficult to recycle.