Sizing a Battery Bank

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Properly sizing a battery bank is key to designing a reliable off-grid system. The principal goal when sizing a battery bank is to install a sufficient number of batteries to carry your household or business through periods when the wind or wind and sun (in hybrid systems) are not available.

Battery banks are typically sized to meet the need for electricity for three days. Longer reserve periods — five days or more — may be required for some areas. As noted in Chapter 3, backup fossil- fuel generators are often included in off-grid systems. Backup generators can reduce the size of the battery bank and are used to equalize the batteries. For more details on wiring and sizing battery banks for off-grid systems, you may want to check out Dan’s book, Power from the Wind. Because batteries are expensive, it’s a good idea to make your home as efficient as possible. This will reduce the size of your wind system and battery bank.