Batteries in photovoltaic systems

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Batteries

"Only Robinson Crusoe had everything done by Friday."
(anonymous)

Roof Integrated PV System PV Noise barrier Wind power Transmision lines

Distributed renewable sources or centralised fossil fuels and nuclear power plants?
(sources: 1,2 - SSES Bildarchiv; 3,4 - Denis Lenardic)

The energy produced during the day, which wasn’t consumed by loads, is saved in batteries. Saved energy can be used at night or during the days with bad weather conditions. Batteries in photovoltaic systems are often charged/discharged; therefore, they must meet stronger requirements than car batteries. Due to the fact car batteries are not suitable for PV systems use! There are many solar battery types available in the market. Most often used classic Pb acid batteries are produced especially for PV systems, where deep discharge is required. Other battery types, such as NiCd or NiMH are rarely used, unless in portable devices. Hermetical batteries often consist of electrolyte in gel form. Such batteries do not require maintenance. Typical solar system batteries lifetime spans from 3 to 5 years, depending heavily on charging/discharging cycles, temperature and other parameters. The more often the battery is charged/discharged the shorter the lifetime.

Battery features

Lifetime depends on charge/discharge cycle rates numbers. The deeper the battery is discharged the shorter the lifetime. The most important battery parameter is battery capacity, which is measured in Ah. Battery capacity depends on discharging current; the higher the discharging current the lower the capacity, and vice versa. Batteries can be charged in many different ways, for example with constant current, with constant voltage etc., which depends on the battery type used. The charging characteristics are recommended and prescribed by different standards. The solar batteries prices are higher than the prices of classic car batteries, yet their advantages are longer lifetime and lower discharging rates. Consequently, the maintenance costs of the photovoltaic system are lower.

Battery related web sites

Any Batteries - Interesting battery related link collection.

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Literature and more information

Battery Technology for PV Systems: Issues for Design and Use.
IEA PVPS; Lead-Acid Battery Guide for Stand-Alone Photovoltaic Systems.
Darden, B.: Battery References & Information Links.
Sandia National Laboratories; Balance of system Publications.