Form Energy reveals the chemistry of its long-duration battery • Hacker News Board

Re: Form Energy reveals the chemistry of its long-duration battery

#141

Post by ComputerGuru » Wed, Jul 28, 2021, 1:16 AM UTC

azernik wrote: post #79

lazide wrote: post #55

Earlier quoted context omitted.

I’m sorry, that really doesn’t make any sense. There is several missing factors here, and it’s a useless metric. Lithium ion can do ‘100 hours’ as well - based on discharge rate. It can also do 10 minutes - based on discharge rate. 100 hours is literally useless on it’s own because it doesn’t tell you anything concrete. 100 hours….. of what? It looks like a classic science writing article where they left all the impo…

100 hours = (kWh/kg) / (kW/kg) - ie capacity divided by the most cost-effective discharge rate.

I agree but that’s a highly misleading number because there’s a conflation of scenarios. Capacity is one thing, useable capacity at the requested discharge rate is another. You can’t pick and choose which numbers to use.

Re: Form Energy reveals the chemistry of its long-duration battery

#142

Post by ComputerGuru » Wed, Jul 28, 2021, 1:49 AM UTC

2Gkashmiri wrote: post #140

lazide wrote: post #124

Earlier quoted context omitted.

Not the parent poster, but do have some familiarity here. Higher battery voltage == less copper, smaller wires for the same wattage. Sometimes also a bit more efficiency too (less resistance, smaller absolute voltage drop moving current around). Your units are a bit messed up load wise - is your computer running at 1 kWh per hour? For how long? (Yeah, that is confusing - but that would be the energy used to power a 2…

Thanks. How we see load is, the product advertises 1000 watts so for me that means 1kwh or one unit of electricity. Same for something that is 200 watts or 2000 watts. I am aware of the solar thing. I have a grid tied system and I sell the energy to grid. I produce around 30 kWh a day which is good. My problem is storage. If I want to store energy, should I go with 48volt 24 ah battery or 12volt 96ah ? As I said, the…

Again, I think you are making the same mistake in your first sentence. 1000W does not mean 1kwh or one unit of electricity. It is a measure of instantaneous (or maximum instantaneous, there’s no way your pc regularly runs at 1KW unless you’re mining) power consumption, the “now” voltage times the “now” amperage (times the power factor… maybe).

For storage, none of that matters. What you need to look at is the cheapest total capacity in kWh after accounting for conversion losses at your median discharge rate. Let’s say your median consumption is 450W, then you see the efficiency of your inverter with 12V vs 48V input to produce a sustained 220V at 450W. Maybe it’s the same efficiency for both 12 and 48v or maybe one is 85% and the other is 80% so you need to multiply the capacity by that amount to get capacity after inverter conversion losses to account for the only difference between the two setups.

Re: Form Energy reveals the chemistry of its long-duration battery

#143

Post by azernik » Wed, Jul 28, 2021, 3:09 AM UTC

ComputerGuru wrote: post #141

azernik wrote: post #79

Earlier quoted context omitted.

100 hours = (kWh/kg) / (kW/kg) - ie capacity divided by the most cost-effective discharge rate.

I agree but that’s a highly misleading number because there’s a conflation of scenarios. Capacity is one thing, useable capacity at the requested discharge rate is another. You can’t pick and choose which numbers to use.

The combination of duration class and capacity is useful, though. 1MWh of 10-hour storage gives you a very clear idea of usable energy.