Many wind energy systems use batteries to supply electricity when the wind is not adequate. A system without batteries will only provide power when sufficient wind is blowing to meet demand.
Not all batteries are created equal, and terminology for batteries can be confusing. One of most important specifications for wind energy systems is Depth of Discharge (DOD). This is the amount of power you can drain from a battery and still have it charge up again.
If you drain 100 percent of a battery's power, you will radically shorten the life of your battery, but batteries for wind energy systems are designed to have a fairly deep discharge and still allow recharging. Usually a 50 percent discharge is used, although some batteries offer up to 80 percent DOD. This means you can safely discharge 80 percent of the battery's power without shortening battery life. Many batteries have low-voltage cut-offs to prevent an excessive DOD.
There are many kinds of suitable batteries for wind energy systems. Deep discharge lead acid batteries are usually the most economical for wind energy systems. Car batteries (lead acid SLI - starting, lighting and ignition - batteries) do not have a high DOD and will fail prematurely if used in a wind system.
Flooded cells are the most common type of battery; they have removable caps for adding distilled water, are low cost, have long life, and will withstand overcharging.
Sealed flooded cells are maintenance-free; they do not require water; they can be damaged by overcharging.
Recombinant flooded cells do not require water; they are more expensive, and can be damaged by overcharging, but will not spill acid.
Gelled electrolyte cells do not require water, are more expensive, can be damaged by overcharging, can be mounted in various positions, and will not spill acid.
The size of your battery system is also important. It may be tempting to buy a small battery capacity to save money, but this will likely lead to a deep discharge and early battery replacement. If batteries are sized correctly for the system, they should last five years or more. Some very high quality large cells can last to 15 years.
It is recommended that batteries be connected in series. Connections in parallel may cause damage because of different states of charge among the individual battery cells.
Specification
Sample Data
Importance
Units
Cell Type
flooded
Specifies the operating characteristics, charging voltage, and maintenance requirements.
Watts or kW
Voltage
12 VDC (Volts DC)
Specifies how many volts the battery has to reach system voltage.
Volt DC (usually 2, 6, 12, 24 or 48)
Capacity
115 Ah (20 hours rate)
Indicates how much energy is contained in the battery, usually for a specific rated temperature and an 8 or 20 hours discharge period; determines how long the load can be maintained.
Amp-hours. The number of amps load multiplied by number of hours the load is applied.
Cycle Life
750 @ 50% DOD
Specifies the number of battery cycles (i.e. discharged, then recharged) before capacity becomes inadequate.
Size
0.3 x 0.175 x 0.2
Indicates storage space required.
Length, width and height (m3)
Weight (including acid)
24 kg
A strong floor or sturdy racks will be necessary for multiple batteries; weight determines if one or two people can move the battery.
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