Batteries

What's Right For You…

Choosing the proper batteries is just as critical as any other component of the renewable energy system. If you plan on being disconnected from the grid, your battery bank/generator is where you are going to receive all your required power. There are three main type of batteries which can be used to store power.

Flooded: this type of battery is most commonly referred to as a lead-acid battery. A flooded battery consists of two lead plates completely submersed in a liquid electrolyte. This type of battery does require minor maintenance, as the water in the electrolyte evaporates as the battery is used. Therefore, distilled water needs to be added to the electrolyte when needed.

Absorbed Glass Mat: these batteries also contain lead plates, however, the electrolyte does not flow freely around the plates. AGM batteries get their name because they contain a sponge like glass matt that absorbs the electrolyte, which then results in no free electrolyte in the battery. These batteries are sealed and use a “Recombinant Gas Effect” to retain their liquid during use. Note: Recombinant Gas Effect refers to the process which sealed batteries used to retain moister in the electrolyte. The positive electrode gives off oxygen, which is then recombined with the hydrogen given off at the negative electrode, which is then condensed and are re-introduced into the battery to keep it moist.

Gel Cell: these batteries are pretty cool, as they contain a gelatin material that suspends the electrolyte within it. This allows the battery to operated in applications where the battery may have to be mounted on its side. This battery also uses the Recombinant Gas Effect to retain moisture in its electrolyte.

Deep Cycle vs. Shallow Cycle

When choosing a battery for your bank, it is important that you make sure it is a true deep cycle battery. Even some automotive batteries will be labeled “deep cycle”, however they generally are not. Automotive batteries are technically shallow-cycle batteries and are only sufficient for short cranking periods. Deep-cycle batteries allow you to discharge time and time again without damage.

Proper Battery Bank Size

Battery capacity needs to be determined by the loads required and the charging system (solar array). Although deep-cycle batteries are designed for heavy discharges, they are like any other battery, in that, the less work they do, the longer they are going to last. A quick way to get a rough idea of what battery capacity will need to be, is you will require ~100 A/Hrs. per 3 A of solar panel current. To get the most performance and longevity out of you bank, try and purchase the largest battery bank you can afford.

Battery Information and Maintenance Tips

To allow your batteries the best performance, they need to be monitored to make sure they are not over charged or too deeply discharged. To protect from overcharging, use a charge controller between the electric generator (wind, solar, hydro) and the battery bank. Also, you want to use a controller with a low voltage disconnect so the batteries are not too heavily discharged. Also, it is important to try and keep your batteries warm (20-22 degrees Celsius) and fully charged. Here is a chart that will allow you to determine the state of your batteries: (resting)

State of Charge	Open Circuit Voltage	Specific Gravity
100%	12.60	1.265
90%	12.57	1.245
80%	12.54	1.230
70%	12.45	1.216
60%	12.36	1.202
50%	12.27	1.190
40%	12.18	1.175
30%	12.09	1.160
20%	12.00	1.148

It is also important to remember to clean battery posts every 3-6 months and add distilled water if needed. Any acid residue that is on posts will decrease efficiency between the batteries and the load source. Also, when doing quarterly checks of batteries, it is a good idea to equalize your battery bank.

Battery Equalization

Batteries need to be equalized after they have been “floated” at low voltages for extended periods of time. The concept of equalization is to equalize the specific gravity in all the cells. So, basically what needs to happen is the batteries need to experience a controlled overcharge. So, your charge controller may either have to be set or bypassed to allow the wind turbine / solar array to provide the batteries with enough voltage. You also need to disconnect all loads that may be connected to the battery bank, as you don't want to damage your 12 volt equipment.

Determining If Your Batteries Are Starting To Age

There are some signs that you will encounter when your battery bank is starting to age:

* Rapid voltage drop under light use
* An increase in water consumption
* Charger shut down early due to rapid voltage increases during charging
* Specific gravity varies between cells by more than 50 points
* Voltage varies between cells by 0.05V-0.1V

As with anything else, you get what you pay for. With a long-term investment, such as solar energy, it is good practise to purchase the best possible equipment. With a good maintenance schedule, your equipment will outlast the manufacturer's warranties.