Replacing a Lead-acid Battery Bank
By George Harvey
In the February 2018 issue of Green Energy Times, there was an article, “Batteries: Lead-Acid vs. Lithium,” in which a number of battery types were discussed (bit.ly/GET-offgrid-batteries). Now, we can look at a process of determining what is best to buy for a specific system.
As many readers know, the editor of G.E.T., Nancy Rae Mallery, has lived for years in an off-grid home. In fact, she founded G.E.T. to let people in on the secrets she found that freed her from dependence on fossil fuels and gave her energy independence. Her electricity is dependent on photovoltaic panels, which provide power and charge a bank of batteries. A propane generator is set up to come on as needed, but whole years have passed without a need to use it.
The batteries have turned out to be the most troublesome part of the system. Having gone through 17+ years of off-grid living, she finds it necessary to install a fourth set of batteries. Understandably, she said, “I don’t want to have to replace my batteries ever again, and I don’t want that generator to come on.”
Fortunately, new technology is available. To be sure she was getting the right system, Mallery has been doing much research and checking the math on what to install. She considered a lot of possibilities from a lot of companies.
She wanted a system that needs very little or no maintenance, can be fully recycled at the end of its life, and is very forgiving if something goes wrong. Her perfect system would have to be capable of being discharged fully without harm to the batteries. It would also have to be capable of getting through an accident, such as a puncture or collision, without catching fire, which many lithium-ion batteries would do. She decided that the best technology for her was lithium iron phosphate (LiFePO4).
LiFePO4 batteries have another important advantage. Even though they cost more initially than lead-acid batteries, their lifetime costs are lower because they last longer.
A number of companies manufacture LiFePO4 batteries. Mallery feels that she could recommend RELiON, SimpliPhi, Sonnen, and Iron Edison to readers, based on her research for lithium options. The choice came to questions of what suitable models were available, specifics of the company warrantees, and company product and engineering support.
Her current system has 24 2-volt Rolls batteries, delivering 48 volts. Her Xantrex SW4048 inverter and the 2 Outback MX60 charge controllers are in good condition. Since the costs of inverters and charge controllers are high, the strong preference was to install a 48 volt battery bank that would work with the existing components and that would store enough energy to last at least 5 to 7 days with no sun. This would mean that she must allow for just under 500Ah of storage capacity, based on current usage. Some options led to a more costly system, partly just due to the number of batteries and more cable connections involved. These facts limited her choices but simplified her search and decision.
Considering the companies involved, she found herself inclined toward the RELiON brand, partly because of the expected longevity and the fact that the engineers seemed very willing to work with her. She asked engineer Craig Quentin, from RELiON Battery Company, what a lifespan of 15 to 25 years meant, in terms of realistic expectations. He said “reliable lifespan estimations are achievable, and 15-25 years is a solid prediction. This is based on the life-cycle testing we have conducted and graphed. At 1 cycle per day and 100% Depth of Discharge (DOD), 5,000 cycles is 15 years. That’s worst case scenario. It only gets better from there with lighter DOD’s and less frequent discharges.”
The remaining questions were what numbers and sizes of batteries in amp-hours (Ah) to use for economic efficiency. Suitable RELiON batteries of 100Ah, 200Ah, and 300Ah are available. She considered the numbers of batteries, numbers of cables, and what size would be most convenient for a minimum system expansion of the system and also for possible increased needs from the addition of an electric vehicle in the future.
In the end, the model she chose was the RELiON RB48V200. Three of these batteries will supply her with 28.8 kilowatt-hours of electricity, an upgrade from her old system. And hopefully, it will provide many years of trouble-free service, and the last battery replacement she will ever have to buy.
Learn more about RELiON batteries at relionbattery.com, or 844.385.9840.
We will look at more battery products in coming issues of Green Energy Times. Stay tuned!