Off grid is silly unless you actually require it. Massive PV overprovision to ensure there's always something on the table is better than insane battery capacity. A couple of weeks worth of storage is a wild amount for a normal household.

I have a 22*980Ah 3.2Vn LiFePo4 array, and it holds a theoretical 13kWh at the 60% "safe" cycling rate (not below ~20%, not above ~80%, 3.0V min to 3.4V max). Taking DC->AC conversion losses into account, that ends up around 11kWh of 230VAC, which is enough for a single "normal" 24h period without generation: that doesn't include hoovering, welding, or running the dehydrator or dehumidifier. The batteries alone were USD$3500; BMS, balancer, cabling, etc. hundreds more. If I take $4000 as the unit price, then 14 days worth of power for us would represent $56k into a depreciating investment. I don't think most people are going to go for that. $56k would pay a lot of electric bills.

I'm in Ireland, which is fairly temperate, and we heat with wood (including the hot water). If you heat with electricity and you want to float that load on battery through a dim February...brutal.

EDIT: holy shitballs, that's $141,189.74 if you buy it as Powerwalls from Tesla rather than parts from Alibaba.

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justahuman74 18 hours ago | parent | next [-]

> $56k would pay a lot of electric bills.

In california, if you have AC and electric car that's 56 months.

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MediumOwl 9 hours ago | parent | next [-]

Is electricity insanely expensive, or do californians use an insane amount of electricity? I just received my yearly bill in central europe, and $56k would pay for approximately 51 years, I'm having trouble reconciling the numbers.

	▲	fragmede 4 hours ago \| parent [-]
		Don't think reasonably sized house, think mansion with 6 bedrooms, a hot tub, a sauna, and a multiple EVs. With peak rates being $0.71/KWh, $1000/month is only ("only") 1400 KWh. High, but for a household of 5 adults, each with their own TV on top of everything else, it's not inconceivable. There's also a discount if you're poor, which translates to a surcharge if you're rich. A smaller household's bill is gonna be a fifth of that, closer to $200 than $1000.

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com2kid 16 hours ago | parent | prev | next [-]

EVs cost ~$2 to charge a day for an average amount of driving.

The cost for AC dwarfs the cost to charge an EV.

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theodric 15 hours ago | parent | prev [-]

My bill was €316 bimonthly at €0.31/kWh before I put in panels. Last bill covering the two sunniest months I've ever seen in Western Europe was €100 exactly, of which in excess of €50 was the standing charge that is due regardless. The remaining ~€25/mo overage is the delta of our demand and the inverter's peak output. Next purchase will be more panels; another inverter would offer only marginal gains.

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ashirviskas 19 hours ago | parent | prev [-]

Huh, your numbers are weird. 22x980Ah of 3.2V cells would give you over 60kWh.

And the price of LiFePo4 continues dropping, it is not a good deal if your cells are aboe $80 per kWh (which at 22kWh should be below $2000).

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theodric 15 hours ago | parent [-]

Fuck. This is what I get for posting on 3 hours of sleep. My hallucinated bullshit came out so close to actual that it looked correct enough.

3.2v nominal per cell, 305Ah capacity: .976kWh per each. Call it .98. Not 980Ah, but 0.980 kWh.

.98 * 22 = 21.56kWh total pack cap.

*0.6 = 12.936 kWh available before conversion losses

We burn about 11kWh daily, so there's about a day in a full battery. Spring/mid summer worked well, but lately we aren't managing to store enough to get through the night, so I will probably add another 10 panels (5s2p) once I can find a grand I don't need.

	▲	ashirviskas 11 hours ago \| parent [-]
		I knew the numbers had to match something! Anyways, thanks for sharing. And please take some proper rest, you protect the batteries using only 60% capacity, but allow your body go below 0%. I'm pretty sure thats out of spec.