If you are installing a solar electric system that will be tied to your utility grid, you will still need deep cycle batteries if you are trying to use power in the event of an outage. Without deep cycle batteries, you can only use power at the time you produce it (i.e. you will not have power when the sun isn't out if you don't have batteries in your solar electric system).
A solar battery must be able to provide long periods of deep discharge each evening and night, followed by a full recharge in only a few hours of sunlight each afternoon. There are several different types of batteries to choose from depending on your system size and your available budget.
Type of Solar Batteries
- RV / Marine / Golf Cart - Light Strength - RV or Marine type deep cycle batteries are basically for boats & campers and are suitable for very small systems. They can be used but do not really have the capacity for continous service with many charge/discharge cycles for many years. Regular or car type batteries should not be used at all because they cannot be discharged very much without internal damage. A very popular battery for small solar systems is the Golf Cart battery. They are somewhat more expensive than deep cycle recreational batteries but are probably the least expensive choice for a small system on a budget.
- Flooded - Industrial Strength - These are Lead acid batteries that have caps to add water. Trojan, Surrette, and Deka are probably the most well known. They are reasonably priced and work well for many years. All flooded batteries release gas when charged and should not be used indoors. If installed in an enclosure, a venting system should be used to vent out the gases which can be explosive.
- Gel - Industrial Strength - Not to be confused with maintenance free batteries, sealed gel batteries have no vents and will not release gas during the charging process like flooded batteries do. Venting is therefore not required and they can be used indoors. This is a big advantage because it allows the batteries to maintain a more constant temperature and perform better.
- AGM - Industrial Strength - Absorbed Glass Mat batteries have a woven glass mat that is used between the plates to hold the electrolyte. They are leak/spill proof, do not out gas when charging, and have superior performance. They have all the advantages of the sealed gel types and are higher quality, maintain voltage better, self discharge slower, and last longer. The Sun Xtender series by Concorde Battery is one example of AGM batteries.