How is Solar Energy Stored?

Both photovoltaic and solar thermal technologies depend on the sun. But what about at night, when the sun is down but you need power? Can solar energy be stored? Below is a description of how storing solar energy for later use.

Storing Photovoltaic Energy

A deep cycle battery. Credit: Northern Arizona Wind & Sun

Solar panels can not produce energy at night or during cloudy periods. But rechargeable batteries can store electricity: the photovoltaic panels charge the battery during the day, and this power can be drawn upon in the evening.

Residential systems usually use deep-cycle batteries that last for about ten years and can repeatedly charge and discharge about 80 percent of their capacity.

While batteries can be expensive, in remote areas it can often be more cost effective to use batteries rather than extending an electricity cable to the grid.

But if choosing to go off the grid in this way, the batteries must be sized correctly, with a storage capacity sufficient to meet electricity needs.

In most cases, though, purchasing electricity from the grid is cheaper than opting for batteries.

Solar Thermal Energy Storage

Residential solar hot water systems – which use the sun’s thermal energy to heat water for the home – have a simpler storage system. Water flows through solar collectors on the roof, and then goes to a storage tank where it can be drawn upon as needed.

Concentrating solar power(CSP) plants use thermal energy to power a generator. While some CSP facilities use water as the heat transfer medium, most new systems us oil or molten salt. These fluids allow the heat energy to be stored for use during cloudy periods or at night.

Parabolic troughs at the Plataforma Solar de Almeria CSP facility in Spain. Photo Credit: PSA.es

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