Last fall, I decided to walk the off-grid walk. Our altE customers have applications that run the gamut, from grid-tied, to battery backup, to off-grid. To get some hands-on experience with the kinds of products altE customers use every day, I took my home office completely off the grid.
Walking the walk, to me, also means not relying on fossil fuels at all. That meant no diesel generator. That, in turn, meant no lead acid batteries, since they need to stay charged when not in use. I needed batteries that didn’t mind standing at partial state of charge when the sun wasn’t shining. The answer was three Aquion Energy S10-008F Battery Stacks.
The batteries were going to live in my family’s home, in the room where I work every day. They had to be safe. Aquion’s non-toxic aqueous hybrid ion (AHI) chemistry can’t catch fire or melt down. Plus, the battery stacks were easy to integrate into my system: I just set them on the floor underneath my inverter and connected the terminals.
The system is comprised of three SolarWorld 250 solar panels, a MidNite Classic 150 charge controller, the three Aquion S10 battery stacks, a MidNite MNPV3 combiner, a Schneider XW4548 inverter, and a MidNite Whizbang Jr. battery bank monitor.
The solar array meets my office’s max 230-watt load. And with more than 5,000 watt-hours of battery storage, I thought I was set with about two days of autonomy. But during the winter at 8,000 feet in the Colorado Rockies, two days just isn’t enough. Days-long stretches of overcast skies are frequent. To keep my office truly autonomous during these bouts without insolation, I needed more storage.
Thankfully, I was able to more finely tune my setup when three more S10 stacks arrived. But they came with a dilemma: how to integrate the new stacks with the stacks that had been cycling for a few months.
To sync them in a single battery bank, I needed to bring all their voltages to within 5 percent of each other. So I fully charged up the older stacks, disconnected them, and charged up the newer stacks. The older batteries dropped a full volt during a couple of days of downtime while I set up the new bank. But all the voltages—56.0, 55.9, 56.0, 55.3, 55.2, and 55.3 V—remained within the comfy 5 percent range.
The new storage bank required some system wiring changes. I switched from a MidNite Solar MNPV3 combiner to an MNPV6 unit, with six 15-amp breakers. I also had to change the battery bank’s wiring to accommodate the increased amperage. The calculated voltage drop index (VDI, which you can calculate using altE’s wire gauge calculator) of 4 indicated that I should use 10-gauge wire.
VDI isn’t always the whole story, though. As you can see in the table below, a 10-gauge wire can only handle up to 30 A. My six-stack system had 90 A, so I went with 4-gauge wire instead.
I also made sure the H4 cables connecting the S10 stacks to the MNPV6 were the same length, so each stack would have the same voltage drop.
With twice as many stacks, my MidNite Whizbang Jr. battery bank monitor showed each stack as having double its actual capacity. To correct the reading to 42 amp hours per stack, I doubled the monitor’s setpoint from 126 Ah to 252 Ah, based on the 20-hour charge rate. I also needed to double the current limit setpoint on my MidNite Solar Classic 150 from 36 A to 72 A (based on Aquion’s recommended 12 A max per S10 stack).
Ever since the upgrade, my off-grid office hasn’t had a single power failure. I have customized my Schneider inverter to bring down the cutoff voltage to its lowest designed setting of 40 V. I’ve also been monitoring the Aquion battery stacks daily via the MidNite Whizbang Jr. and the My Midnite website, and so far the bank hasn’t dropped below 51 V.
As I’m writing this blog, I’m currently in my third day of cloudy, rainy weather in the Rockies, and the office is still running strong.
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