Using Batteries to Power Your Off-Grid Homestead

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Deep-cycle batteries
Deep-cycle batteries
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Batteries play a central role in providing power to  your homestead.
Batteries play a central role in providing power to  your homestead.
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A battery bank's enclosure should be ventilated and isolated from the home.
A battery bank's enclosure should be ventilated and isolated from the home.

A properly sized, well functioning battery bank is the heart of any off-grid electrical system. It absolutely makes the difference between days filled with pleasant convenience and complete, ongoing frustration. Anyone who is considering going off-grid (and those already in the frying pan with inadequate systems) should become a battery aficionado long before buying the first (or next) piece of solar, wind, or hydroelectric equipment. Bad battery advice is easy to come by, and the dangers of misusing battery banks are very real. So let’s get down to business.

The types of batteries used for off-grid system storage are called deep-cycle batteries. Don’t be conned into trying auto motive batteries for this application (one of the most common bits of bad advice); they just aren’t designed for it. If they were, solar catalog companies would sell you batteries rated in cold-cranking amps rather than amp/hours. The two most widely used types of deep-cycle batteries for home power systems are lead-acid (cheaper, more common) and nickel cadmium. These have two very different personalities, which you should consider before choosing what’s right for you.

But before talking about each, there is a rule pertaining to both that should be followed: never mix and match batteries.

In fact, never even mix and match same type cells of different ages. The optimum situation is to buy all new cells at one time, use them for their lifetime, and then replace the whole set. If you come across used batteries, always get the exact same cells for the entire bank, and try to get ones that have already been together or, at the very least, have had similar usage. This rule has to do with the voltage of each cell within each battery running consistently as close to all the rest as possible. When an imbalance in voltage occurs, some cells stay topped out or receive too much voltage, while others never fill.

When considering lead-acids, remember that they are temperature-sensitive. A lead-acid cell has half the capacity at 25°F that it has at 80°F The result is that the colder the bank gets, the quicker it will both charge and discharge. You’ll want to take this into account to avoid working with half the power when the days are shortest.

  • Published on Feb 1, 1999
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