Batteries are the heart of your off-grid solar energy system. A battery stores electrical energy as chemical energy and releases it on demand as electrical energy. You can take energy out faster than you put it in, but in the long run you can't take out more energy than you put in.

The energy your solar panel generates from sunlight comes at varying rates, depending on the angle of the sun, the amount of cloud cover and shade and the number of hours of daylight. The energy you use will come at different times and at different rates, so you need batteries to store energy for when it's needed.

A charge controller controls the flow of energy from the solar panel to the battery by turning the flow of current on and off for varying amounts of time. The battery receives electrical energy at the maximum rate it can safely be converted to chemical energy. When the maximum operating voltage is reached, the charge controller cuts off the flow of charging current. Many charge controllers also have a load disconnect capability to protect the batteries from over-discharge.
  
Automotive batteries can't be used in solar energy systems because they will fail after only a few discharge-recharge cycles. Deep-cycle batteries are needed. In a solar energy system using deep-cycle batteries, they can be discharged safely to 50 percent of maximum capacity before recharging.

Why might you need more than one battery?  One battery can store a fixed amount of energy. Suppose you fully charge your battery in one day. Then any more energy delivered from the panel is just dumped. You are wasting the money you put into your panel and charge controller. Then, after several days, you start using energy at a high rate and your battery discharges to half capacity, then you can't use your electrical appliances. So you aren't getting what you paid for. In this case, you need more than one battery, perhaps two to four batteries connected in parallel. Your usage pattern determines how many batteries you need.

All Your Solar Answers in One Place

Batteries for Solar Systems

Some Useful Definitions
(To Help you understand how we will calculate the size of solar system you will need)

Amperes measure the current (or quantity of electrons) pushed through a wire or appliance.  For example, your hair dryer may be rated as 15A at 120Volts.
Electricity is measured in Volts (V), amperes (A),Watts(W)and Watt-hours (W/Hr).
Volts measure the electrical pressure that pushes electrons through a wire or appliance.  For example, a deep-cycle battery normally provides 12V to 13V.

Watts measure the power resulting from a voltage pushing an amperage.  For example, a TV operating at 120V and 0.5A uses 60 watts (W).

Watt-hours measure energy consumption, that is the number of watts of power multiplied by the number of hours the power is used.  so a 13 watt compact fluorescent bulb operating for 10 hours will use 130 watt-hours
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