blog Sustainability Tech

Breaking the Battery Bank

I’ve been studying going solar for energy savings and disaster prep… and even with recent improvements in battery capacity things are looking rough.

We use about 100KWH a day… Sometimes a lot less, but sometimes a lot more. Yeah, that’s a lot, but our in-law suite alone is almost the size of my old house.

That much power draw requires a bank of around 16,700Ah at 12 volts… Technically we are only drawing around 8,400Ah a day, but everything I’m reading says that you can’t go below 50% charge on Lead Acid batteries. Lithium Iron Phosphate can go lower without degrading battery life and can handle more cycles, but also costs nearly twice as much, so while the long-term savings are solid, the initial outlay is significantly more.

Batteries cost between $2-$4 per Ah, depending on whether you go Lead Acid or LiFePo4. This means that going 100% off-grid with a mere 24 hours of backup for cloudy days would cost in the neighborhood of $50k… just for the batteries.

I felt like I was messing up my calculations somewhere, since the F150 Lightning is supposed to power a house for several days, so I went and checked on that. Tests and teardowns seem to indicate that the F150 Lightning has a 110 KwH battery, which an online calculator tells me is about 8,000Ah… and I imagine that those numbers are the accessible charge, not draining down to zero, since I can’t imagine Ford would release a vehicle that would be unrecoverably dead if you accidentally drove it down to zero.

So that kinda checks out.

Double the 8,000Ah of a F150 Lightning, throw in some inefficiency for operating in a 50 degree basement and using scraped together parts, and a Lead Acid battery bank probably does need to be around 16,000Ah.

We essentially have two houses on the same utility account and have very old HVAC units, so you can probably figure a modern house eats around 60KWH a day, which a Lightning would indeed be able to supply for a few days…

And Google now tells me that the average household uses about 30KWH. Huh, I guess I need to prioritize getting new HVAC units, because 100KWH per day is bonkers. I guess we’ll start with saving energy and maybe getting some solar panels, if they pay for themselves, because if I can find a way to halve our energy usage, that makes the goal of being able to go off-grid in an emergency more attainable.