I'm no expert, but I'd imagine figuring out a (safe) way to use it with your water heater would be the low-hanging fruit, in terms of least-complexity for the amount of grid consumption you'd potentially save.
this post was submitted on 29 May 2024
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That's an interesting idea. A water heater is a really underutilized battery that most households have. I suppose you could hook it up to a thermostat with a set point a couple degrees higher than the mains (or gas) powered thermostat.
A quick search says in my location with a 100W panel, I'll generate 400Wh as my daily average (1.44 MJ). With a 150 L tank, that gives you about 2.25 K increase in temp for a day.
That's not nothing.
Get a DC to AC converter, plug your computer into it, and mine Monero.
I had a spare 50W panel and charge controller that used similarly for camping. Had more or less the same thought as you: I should use this year round.
Ended up building a wooden box with a couple of old car batteries inside along with the controller. Kept it outside and ran a cable inside carrying 12v (make sure you put an inline fuse after the battery in case it short circuits along the way. Used the 12v from that and some old car chargers to set up a charging station for all my devices.
The car chargers were all random plug styles since they were from a box of stuff I've accumulated over the years, so I cut those off and spliced on USB-A female ports so they could charge any USB device. Worked great.
If I had to do it over again, I'd do it similarly but use 12v USB-C power-delivery adapters instead so I could charge bigger stuff like my laptop.
3 years seems pretty good for using a car battery outside of it's preferred use case. I guess that depends on how good/bad you were about deep cycling it.
Currently, the batteries I'm using are my power tool batteries, which are 18V so they charge through a dedicated (12V) charger, and I have a little USB A/C and low powered inverter that uses them. I probably wouldn't necessarily want to put my lithium batteries through every day cycling, though.
I've thought about generating hydrogen with it to use for experiments and such, but idk if I have the space for that.
Awesome effort! If not done already, you may want to look into venting that outside box. I believe there are examples of the out gassing of enclosed lead-acid batteries causing corrosion of nearby metals. Hilarity ensued.
It doesn't exist anymore, but yeah, good call. I never replaced it once the batteries finally gave out, and I moved less than a year later.
It did have vents on the sides for airflow, but that was more of a consideration for heat build up and keeping the controller from cooking in the summer. It was also less a "box" and more like a small doghouse (including shingles lol). I atually gave it to a neighbor after I was done with it; they cut a hole in the door and used it as a cat house.