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How much should you pay for batteries ?
#1
I thought I would post and explain from my experience as it seems like a few people are paying far more than they should be for cells.

How much you pay depends on the question of how much it really costs to put 1kWh into and out of a battery pack ? If you want power off grid then the question varies a bit because it is not all about competing with the utility price.

You first have to take into account the cost of the battery and divide this by your expected cycle life energy. You have to calculate the equivalent £/$ per kWh of storage. The cost per kW is in part irrelevant at this stage, otherwise buy a supercapacitor.

Say my 3.7V cells cost me £/$ 1 each, are 2Ah and I expect them to last another 500 cycles before chemical recycling.

Volts X Amps = Watts
3.7 x 2 = 7.4W per cell capacity or 7.4 Watts for 1 hour or 7.4 Watt Hours (7.4Wh).
7.4Wh over 500 cycles = 7.4 x 500 = 3700 Watt Hours or 3.7kWh
Cost / kWh = Throughput cost
1 / 3.7 = 0.27/kWh throughput cost

This is effectively how much it costs to put energy in and get energy out at $1/cell at 2Ah and expect it to last 500 cycles.

If your grid supply cost is less than 0.27/kWh then you are better off buying from the grid (this is before even taking into account the approximate 20% losses getting the power in and out of the pack). I would argue that $1/used cell is way too high. Even half $0.50 / cell is borderline.

Buying at Korishans level of $1.25/lb for say 6 cells or £0.21/cell (10 Mar 02:44AM post) gives a throughput cost (assuming 500 cycles) of $0.057/kWh (5.7c/kWh) and looks very viable, even for on grid with a multi rate electricity tariff. With solar/wind as your additional power source you are laughing...

The interesting bit is how many cycles will a cell really last in any useable form before it has a negative effect to the whole pack as 500 may be too low when using them down to 10% capacity level ?

What I would like to know is what are your expectations, experiences and calculations for throughput cost and what your rationale is for a given price at which to buy cells ?
iomagico, Headrc, Korishan like this post
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#2
This is a very good break down. I haven't thought of it like this before, but makes absolute sense. Albeit, this does not calculate the cost of the time put into building everything. So how much is your time worth, is something you need to figure in as well.

I currently pay about $0.13/kWh. So with the calcs above, I'm borderline with my current setup. But I also plan on getting cells cheaper in the future.

This math may very well make it into the FAQ for future readers Wink
Headrc and 100kwh-hunter like this post
Proceed with caution. Knowledge is Power! Literally! Cool 
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#3
As a very good old person told me - your time is the most valuable commodity on the planet, invest it wisely.
Korishan, 100kwh-hunter, Crimp Daddy And 1 others like this post
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#4
That's what I've been saying almost from the start. And it's even more complicated because how do you value your time? How do you value the ecological impact? It's not easy at all to make a sound calculation that gives you a result that you can use to make up a definitive yes or no.

Paying for used batteries is already a bad start. You have to get them free or for a very low cost, we're talking about cents per piece. If you don't and pay the insane prices some people ask for then you have to increase the value you see in using reclaimed cells because otherwise this is already a bad economical decision before you have even started.
And then, if you decide to do it, you have to price in your work hours. Reclaiming 18650s is a very inefficient way to get cells to build some energy storage.

You can buy big cells today at 1.00 to 1.50 EUR per Ah that can be assembled into a battery in a matter of minutes and will give you thousands of cycles.
Headrc likes this post
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#5
The learning experience is why I have kept working on my battery even when it became uneconomical price wise . Besides gives you bragging rights, yes I built my second hand electrical storage device, then you have to explain that it is a Big Battery. plus I needed something to do.

Later floyd
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#6
I'm currently getting laptop batteries for ~ $0.40-$0.50/lb, but who knows how long that'll last for. I live in an area that doesn't currently have any competition though, and the only scrap metal place in town stopped buying laptop batteries altogether, so I'm the only way many places can get rid of them.
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#7
Wink 
What area is that?  Can I move there?   Tongue
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#8
(03-12-2018, 03:22 PM)Headrc Wrote: What area is that?  Can I move there?   Tongue

Watch out !!! you can start a lithium rush this way...
Your area can be flooded with 18650-diggers very fast  Wink
100kwh-hunter, hermitdave, Korishan like this post
___________________________________
18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: https://secondlifestorage.com/t-Instant-powerwall
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#9
Yeah the 2018 Lithium rush! Big Grin
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#10
(03-13-2018, 12:29 AM)Headrc Wrote: Yeah the 2018 Lithium rush! Big Grin

Energy storage is the new frontier
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