Deep Cycle Batteries

All About Batteries

Batteries provide electrical storage in renewable energy (RE) systems. If you want to use your electricity anytime other than when the system is producing it, you will need batteries. So if, during a nice sunny day, your solar array produces a lot of electricity, you’ll need batteries to access that power after the sun goes down. And although it may seem counter-intuitive, it’s also true that if you have a wind turbine or solar panel array that is connected directly to the Utility Grid without batteries, you will not be able to use the power they produce during a grid power outage. If you need to be able to use power at any time, you need batteries. But which ones? The first thing to do is to identify the type of battery you will use in your system.

Deep cycle batteries

Batteries used in RE systems are different from car batteries and that difference is critical. RE systems by nature are cyclical: energy is captured and stored, then later consumed, in a (usually) regular charge cycle. For example, in a battery-based solar electric system, the energy produced daily by the solar panels is stored in the battery bank, which is then used by loads at night or on not-so-sunny days. This repetitive process subjects the batteries to a slow, daily charge and discharge pattern. Car batteries are not meant to be used in this way. They can release a great deal of their stored energy at once, to start the engine, then they immediately receive a rapid recharge from the car’s alternator. They’re not meant to recover their charge slowly, as would happen in a solar electric system. They’re very impatient that way! In fact, a car battery in a RE system would quickly die and need to be replaced. Deep cycle batteries, on the other hand, can be gradually discharged by as much as half of their capacity and will patiently await gradual recharge. When properly maintained, a deep cycle battery can last four to 10 years.

There are two divisions and three main types of deep cycle batteries used in RE systems. The divisions are flooded and sealed batteries. Flooded batteries use a fluid electrolyte, have ports to access their cells’ fluid reservoirs, and require maintenance (adding fluid). Sealed batteries use non-fluid electrolyte contained in inaccessible cells. There’s only one flooded type: flooded lead-acid batteries. Sealed batteries include AGM batteries and gel cell batteries.