Solving the Achilles Heel of Battery Storage
A Nickel Iron battery bank. Minimum and maximum water lines are marked on each cell to indicate when watering is needed. Photo courtesy of Iron Edison.
By Luke Simmons
Going “off the grid” and using the sun or wind for electricity can be a liberating achievement – gaining independence from utility companies, reducing dependence on fossil fuels, and taking a giant step towards a sustainable lifestyle. The heart of a typical off-grid system is a set of flooded deep-cycle batteries, which require periodic refills of distilled water. But, relying on store-bought water in plastic containers is hardly sustainable, and some are finding distilled water shortages at their local grocers.
“This one issue could easily turn into the systems’ Achilles Heel if a situation arose where we couldn’t get to a store so we could buy distilled water,” said Tammy Reiss, who lives off-grid and uses around a gallon and a half of distilled water per week in her household’s nickel-iron battery bank. “I also cringe having to buy all those unsustainable plastic jugs that the distilled water comes in.”
Tammy and her husband Matt say becoming more self-reliant is what sold them on an off-grid solar powered battery storage system in the first place. Their battery bank consists of 20 Iron Edison nickel-iron cells; each cell is 1.2 volts and 300 amp-hours. The cells are wired in series to make a nominal 24 volt, 300 amp-hour battery bank. The individual cells are in a clear casing with minimum and maximum water level lines marked, so it’s easy to see when water needs to be added.
As a flooded battery recharges, electrical energy is converted to chemical energy and water in the electrolyte evaporates. Watering is typically required every four to six weeks, but in hot summer months when solar exposure is the highest, watering can be required every week. Both lead-acid and nickel-iron chemistries require these periodic distilled water refills.
Matt and Tammy say they grew tired of going store-to-store looking for distilled water and began researching home water distillers. They eventually settled on a one-gallon capacity model from American Water Distillers for under $100. The unit has a total draw of 720 watts and is rated to make a gallon of distilled water in four hours.
“We found putting it in a cool area, like our basement, cuts this time by a half hour,” said Tammy. Water vapor condenses more easily on a cool surface.
The Reiss’s used to pay $1.29 per gallon of distilled water in upstate New York. Now, the water costs nothing and is distilled by excess energy from their solar array. Matt usually distills twice a week, on sunny days when his solar panels are producing excess energy.
“What’s great is the whole system is fully sustainable now,” Matt said. “I don’t have to worry about getting to a store; I can make my own [distilled water].”
For those looking to distill their water at home, Matt advises that higher wattage does not necessarily indicate a more efficient distiller. Further, stainless steel models are recommended, as impurities from plastic could seep into the water and damage a battery.
While some may attempt to make their own homemade distilled water, using coffee makers or self-constructed units, the end product may not be suitable for batteries. Most such equipment does not actually distill the water. The minerals and ions found in tap water can harm the metal plates inside a battery and reduce its capacity and longevity.
“There are a lot of do-it-yourself instructions on the web on how to build or acquire distilled water,” Tammy explained. “If you can’t guarantee 100% pure distilled water as the end result, do not use the end product in your batteries.”
Using sealed lead-acid batteries, which don’t require any watering maintenance, is another option for off-grid systems. But they don’t last nearly as long as their flooded counterparts, and contain lead which is difficult to recycle and toxic to the environment.
The Reiss’s nickel-iron battery bank is rated for at least 30 years of service. It is fully recyclable and environmentally friendly, containing no toxic elements.
Luke Simmons is a system designer and sales manager at Iron Edison Battery Company. He is NABCEP-certified in PV Technical Sales and specializes in both grid-tied and off-grid renewable energy systems. He can be reached at (720) 432-6433 or luke@ironedison.com.
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