Batteries for solar systems

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Using batteries with solar energy systems can enables the system to operate off the electricity grid.

During the day, energy from solar and/or wind generation is stored in the batteries.

During the night or periods of low energy production, the energy stored in the batteries can be used to power the residence via the inverter.

Many inverters do not support the use of batteries. To incorporate battery storage in your solar energy system you must purchase an inverter model that supports batteries.

[edit] Units of Battery Capacity: Ampere Hours

The energy stored in a battery, called the battery capacity, is measured in either watt-hours (Wh), kilowatt-hours (kWh), or ampere-hours (Ahr). The most common measure of battery capacity is Ah, defined as the number of hours for which a battery can provide a current equal to the discharge rate at the nominal voltage of the battery.

The unit of Ah is commonly used when working with battery systems as the battery voltage will vary throughout the charging or discharging cycle. The Wh capcity can be approximated from the Ahr capacity by multiplying the AH capcity by the nominal (or, if known, time average) battery voltage.

A more accurate approach takes into account the variation of voltage by integrating the AH capcity x V(t) over the the time of the charging cycle. For example, a 12 volt battery with a capacity of 500 Ah battery allows energy storage of approximately 100 Ah x 12 V = 1,200 Wh or 1.2 KWh. However, because of the large impact from charging rates or temperatures, for practical or accurate analysis, additional information about the variation of battery capacity are also provided by battery manufacturers.

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