Deep Cycle Batteries

Battery Bank Sizing: Off Grid Solar Power System

Check out our instructional video on deep cycle battery sizing for solar and wind power systems. The video shows you the calculations for doing load analysis and battery bank capacity calculations.

Deep Cycle Batteries for Solar Power Systems

Solar Batteries (Deep Cycle Batteries) are a key component in a stand-alone renewable energy system. If you are installing a wind, solar panel or hydroelectric 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).

In renewable energy systems, deep cycle batteries provide the energy storage for your system. Unlike your car battery, deep cycle batteries that are used in renewable energy applications are meant to be discharged and recharged (cycled) repeatedly. To maintain healthy batteries and prolong battery life, most manufacturers suggest limiting the depth of discharge to about 20%. (That means the deep cycle batteries will be at 80% capacity or better.) At the very least, do not allow the batteries to be discharged below 50% Depth of Discharge (DOD). Often an inverter will have a Low Voltage Disconnect feature that will disconnect loads at a given set point. Low voltage alarms can provide audible warnings as well. Ammeters, Voltmeters, Battery Monitors can help better maintain deep cycle battery health and provide statistics about the overall health of the system.

Types of Solar Batteries

When selecting deep cycle batteries for storage from your solar array or wind turbine, you'll have the option to use flooded lead acid (FLA) batteries or sealed batteries (AGM or Gel cell). Keep in mind that FLA batteries require a bit of maintenance, however, they generally last longer than their sealed counterparts. Water miser vent caps, which reduces battery watering, can reduce the frequency that the deep cycle batteries need watering. You'll need one vent cap for each 2 V cell.

Desulphators are a Great Way to Extend Deep Cycle Batteries' Life

Desulphators are another good low cost investment that can help prevent sulfation and boost the performance of the batteries. Flooded Lead Acid deep cycle batteries can build up sulfate crystals on their lead plates over time. Our desulfators "shake" these sulfate crystals off the surface electronically and can actually save the life of a battery that would otherwise be thrown out.

Deep Cycle Batteries Range Widely in Weights

Deep cycle batteries come in many sizes: From batteries that are less than 10 pounds to ones that weigh over 200 pounds each! They can be small (and fit in a backpack) or large (2' x 2' x 1') and anywhere in between. Generally, the size and weight correspond with amp hours of storage. So if you need a lot of electrical storage, be sure that you have the appropriate space to house the batteries and brawny people to help you put them in place.

Whether you have one battery or a bank of 36, proper storage is essential. Battery boxes can provide a neat and safe way to contain the batteries or you can build your own battery box. Often people add an optional battery ventilators or battery fans that can vent the hydrogen gas that is naturally exhausted by the deep cycle batteries charging.

Deep Cycle Batteries Storage Capacity: Battery Bank Sizing

Deep cycle battery banks consist of one or more batteries, and are measured in amp hours of storage capacity. Each deep cycle battery can be 2, 4, 6, or 12 volts DC (Vdc). The choice of individual solar battery voltage will depend upon your total system voltage (12, 24 or 48 Vdc) and your desired amp hours of storage. Often the 2V deep cycle batteries offer the largest amount of storage; however, you may need up to 24 of these huge deep cycle batteries, if your system is 48 volts. Also, see our video above on Battery Bank Sizing for Off Grid Home Solar Systems, that will cover the calculations for load analysis, battery bank capacity, array wattage, charge controller and inverter sizing.

Wiring Up your Deep Cycle Batteries

Connect your solar batteries (i.e. deep cycle batteries), using solar battery interconnect cables, in series, parallel, or a combination of both depending upon your system voltage and the storage capacity you need. Read more about this in the how to section about deep cycle battery bank sizing. While deep cycle batteries may be a large expense for a sizeable off grid system, with proper care and maintenance, they should last 5-10 years. Let us know how many watt hours per day you need to provide, and the number of days of storage you need, and we'll be happy to offer specific sizing recommendations for your deep cycle batteries.