A Battery is an Electrical Energy Storage Device

A battery is the center of your solar electric system. Batteries store energy/electricity, they don’t make it. You need a battery to store the energy you’ll collect from the solar panels (or it could be wind turbines, or whatever).  You have to put it somewhere. Using a consuming device directly attached to a solar panel without some sort of battery buffer or collection system, like feeding back into the grid, doesn’t happen too often in real life. It’s too unreliable. You need a battery.

What kind of battery, how physically big it is, how it’s made, and how much electrical energy it holds are good things to know at least a few things about. Do-over’s can be expensive. Batteries for solar electricity could cost under a hundred dollars, or several hundred dollars or more. What makes it right is that you know what you’ve got and it does what you need for it to do. How batteries are built and how they’re used sets them apart.

Deep Cycle Battery - Solar

The battery type most used, by far, for solar applications is the 12 volt Deep Cycle battery. Sometimes it’s referred to as a Deep Cell battery or a Deep Discharge battery, but Deep Cycle is the most correct term. These batteries are designed to be repeatedly discharged up to 80% time after time, for years.  

The battery of any size similar to this you’re most likely familiar with is the one in your car which is probably also 12 volts. But, it’s different. The one in your car is built to provide a large current but for a short period of time. It’s a ‘starting’ battery. Technically, ‘starting’ batteries have more instant power than 12v Deep Cycle batteries do.

‘Starting’ batteries have thin “plates” to provide lots of surface area for that initial cranking oomph. Deep Cycle batteries have thicker plates. Less initial oomph, but better long term cycling capabilities (a cycle means a discharge with subsequent charge). You may have an extra/old car battery you’re thinking of using. Just know if you use a ‘starting’ battery like you would a Deep Cycle battery (repeated discharges) it could fail after not too long, as few as 30 discharges, depending on its condition. Starting batteries are not designed for repeated deep discharge – doesn’t mean you can’t use one as long as you understand it’s limitations.

Choosing a Deep Cycle battery would be easier if there were only one kind. But, there are lots of kinds.  And, many are not true Deep Cycle batteries. And more than that, it’s hard to tell. Some of the lower end ones are called Deep Cycle Marine batteries. A good word for them might be ‘hybrids’. They’re sort of a ‘Deep Cycle – Starting’ combination. But they’re less expensive and they work, especially on smaller systems. You can pretty much assume that if a battery is on the lower end expense wise it’s probably a hybrid of some sort whether it’s mentioned or not. But that’s not a horrible thing.  

Deep Cycle battery prices vary. You can spend about $90.00 on a 12 volt Deep Cycle (probably a hybrid) battery at any discount store that sells batteries and it will work, or spend hundreds of dollars to get a super smashing, true 12 volt Deep Cycle battery that will work much better – as in hold more energy and last longer. The question for you is, for your purpose, do you need “better”? Or is good enough, enough?  Totally depends on what you need/want to do.

Types of Batteries -  Page 2