Commercial Batteries
All standalone and battery'backup PV systems require battery storage. Photovoltaic modules charge the batteries during daylight hours and the batteries supply the power when it is needed, often at night and during cloudy weather. Utility gridtie systemds supply power directly to the utility grid; no battery storage is needed.
A deep-cycle lead-acid battery is designed to be regularly deeply discharged using most of its capacity. A deep-cycle battery is designed to discharge between 50% and 80% depending on the manufacturer and construction of the battery. Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge, as there is a direct correlation between depth of discharge on your battery and the number of charge and discharge cycles it can perform.
A deep-cycle lead-acid battery is designed to be regularly deeply discharged using most of its capacity. A deep-cycle battery is designed to discharge between 50% and 80% depending on the manufacturer and construction of the battery. Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge, as there is a direct correlation between depth of discharge on your battery and the number of charge and discharge cycles it can perform.
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- Sizing Information - Sealed Batteries - AGM vs. Gel |
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Sealed Batteries Sealed batteries are the choice for emergency backup power systems, and they're a good choice if batteries are going to be moved regularly, or if regular maintenance isn't practical. You'll find sealed batteries in computer UPS power supplies, in all those portable battery pack gizmos to start your car or inflate your flat tire, in many self-powered medical equipment pieces, in most automatic gate openers, in cordless electric trimmers and lawnmowers, and in a lot other surprising places. They're clean, spillproof, and easy to live with. But in return they're more expensive, and they're a little fussier about their charging. Sealed batteries should not be subjected to charging voltages above 2.35 volts per cell (14.2v for a 12-volt battery), for anything more than a few minutes. In a more or less fully charged battery, higher charging voltages would produce gassing. This creates pressure in the battery. Since exploding batteries are an unpleasant concept, manufacturers install one-way pressure relief valves. But that venting gas is water that you've lost from the battery with no way to replace it. A charge controller setup for perfectly acceptable wet cell battery charging at 14.8 volts, will kill a sealed battery within a few months. So make sure your charging sources are setup properly when you install your expensive sealed batteries. AGM vs. Gel There's two ways to build a sealed battery, and both claim that their way is superior. We sell both kinds, so here's the honest scoop. Absorbed Glass Mat uses a fiberglass-like material between the cells to hold the liquid electrolyte. AGM batteries are by far the most common sealed battery type, are easier to make, generally cost a bit less than gels, and because their electrolyte is more liquid, can tolerate higher charge and discharge rates. But because they're almost starved for electrolyte, AGM cells are more easily damaged by overcharging. They can't afford to lose any water. Gel cells use a jellied electrolyte with more liquid content, and are more tolerant of the occasional overcharge. But they absolutely must be assembled without any air bubbles or voids, so they cost more to build. The extra cost may be offset by the extended life expectancy gels typically offer -- 20% to 30% longer regardless of the cycle depth. |
