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Comment by opwieurposiu | Hacker News Reader

I have bought a few used electric car batteries for diy solar projects on ebay recently. I have paid $200-$250/kwh.

For example a Tesla Model S battery module, 24V, 250Ah,5.2kWh, Panasonic 18650 3200mAh cell is going for $1,045.00 + 150 shipping.

That is $229/kwh shipped. For most of these batteries you will also have to buy a BMS and/or cell balancer.

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That’s pricey per kWh - lithium tech generally is. I’ve just installed an off-grid solar system, and ended up putting together a spreadsheet of a whole bunch of battery options, got prices per kWh, and then built in a factor for lifetime/max cycles.

Ignoring max cycles, the cheapest lead acid I found was £87/kWh. Lifetime was poor, however.

The best bang for buck was OPzS lead acid cells - £115 per kWh, and a long, long lifetime and high cycle count. They’re the most commonly used cell in new grid-scale solar installs, and it turns out there’s a reason for that - over 15 years, they cost less than 20% of lithium over the same period.

That's true but those lead acid cells are only practical for stationary installations. They are far too heavy to use in vehicles.

Would you be able to share your research?

Sure. It’s scratty as sin as it was purely intended for my consumption - you can safely ignore the sheets other than batteries - panels are a pretty simple equation - more power is better, and usually cheaper per surface area, and the other gumph was specific to my requirements.

You’ll note the total absence of lithium cells - I took them out as they skewed the scale so badly that it was hard to differentiate between the others.

Also, all the prices are EUR, and I should have said €, not £, in my previous comment. Living between U.K./EU and being paid in USD sees me forgetting what currency I did something in quite frequently.

https://docs.google.com/spreadsheets/d/1w8vPBHkMyY5jvkxtK1Qh...

Where are you finding these OPzS cells?

In Europe - I bought 24 BAE Secura 6 (900Ah at C100) cells from an outfit called merkasol - they’re pretty commoditised and the prices are similar from different distributors. Went for those as they were the biggest OPzS cells I could safely carry by myself, at 60kg, and 42kwh of storage is plenty.

That seems kind of expensive still. Grid power is around 7 cents / kwh for comparison so you need over 3,000 hours of usage to break even on a depreciating battery. Or for comparison, new 18650 cells are around $2 each in bulk, so you could get almost the same kwh storage (probably 5% less) for the same price, with a lot more cycles left.

I don't know how much it adds, but the Tesla model S module has to have rigidity for the car and some puncture resistance etc. that might not be needed in a power application right? It also may need to have a much higher peak discharge and charging rate and cooling to accommodate that.

That's true. A vehicle-grade battery pack should also already come with the wiring built in so you can charge and discharge all the cells from a single point without having to make your own harness. Still, though, I'm not convinced buying a used Model S battery pack is a good deal unless you have an application that specifically needs it.

grid power where?

For PG&E in california, grid power is .23/.29/.51 per kwh (tiers depending on usage)

Here in Portland [1].

[1] https://www.portlandgeneral.com/residential/power-choices/ba...

You are forgetting delivery charges. It's between 0.11 and 0.12, with appropriate charges.

That's fair, but it doesn't really change the main point that you're looking at a stupid amount of hours equivalent to get to break-even while adding hundreds of charge cycles to an already-degraded battery. I can't really see this being a positive ROI purchase unless you want to use it for a vehicle. Used battery prices need to come down another 20-30% before it will make sense.

I would love to get that from PG&E in California. As it is, and with the high cost of energy in datacenters (because it's triply redundant, etc.) I've been researching natural gas power generation at home to power my render farm, instead of putting it in a datacenter.

I can do it for about $0.17/kWh, which is cheaper that the energy I get from PG&E. Fixed cost for the generator is about $7K to power the farm.

i'd factor in wear and tear on the generator there too they aren't meant for 24/7 use.

I'm surprised seeing that power-source chart for OR. In particular 60% NatGas+Coal, 30% hydro, 6% wind. Any idea why so little wind-power development yet?

It's not 3000 hours of usage, it's 3000 cycles.

Where are you seeing them for this price? That's significantly lower than I've seen.

https://www.ebay.com/b/Electric-Vehicle-Batteries/177703/

I have bought a few different kinds, The honda cells are currently my favorite for their build quality but they are not the cheapest.

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