How much should you pay for batteries ?

completelycharged

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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 ?
 

Korishan

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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 ;)
 

DarkRaven

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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.
 

floydR

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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
 

Joey Kendrick

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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.
 

wim

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Headrc said:
What area is that? Can I move there? :p

Watch out !!! you can start a lithium rush this way...
Your area canbe floodedwith 18650-diggers very fast ;)
 

Spazmor

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You wouldn't fully drain the 2000mah every cycle though would you? because you'll try to extend the lives of cells. so.. maybe 70% of 7.4Wh = 5.18Wh
 

Korishan

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Spazmor said:
You wouldn't fully drain the 2000mah every cycle though would you? because you'll try to extend the lives of cells. so.. maybe 70% of 7.4Wh = 5.18Wh

Sorta correct. It depends on what you did the test on from low voltage to upper voltage. But, generally speaking, the tests are done from about 4.2V down to 3.2V or 2.8V (depending on the charger and your settings). Then use the voltages from 4.1V to 3.2V as the working voltage. So yeah, you use about 70-80% of the tested capacity. Thats why it's good to have about 1/3 more than what you actually would need.
 

Saucebeast

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Good read, thx all for posting. Im not entirely concerned with competing with the grid, the environmental bit is big for me. Im in Miami and Im bracing for more hurricanes and more flooding, besides the fact that I hate messing with fuels and ICEs, the gas frenzy leading up to Irma was real. I for one love the modular nature of diy cells. I plan on one day converting a car and my boat to electric and I can then move cells around to power whatever Id be using. The benefits are kinda endless for me.
 

cheamc

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In my country, the grid cost is so cheap that it didn't justify to make all this powerwall or battery bank. No matter how you calculate it.

It is just for hobby and interest. And such hobby parts are expensive to buy.
 

completelycharged

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If your country is subsidising the electricity then this does make your own power wall a difficult proposition. In the majority of other countries where the power cost is representative of the actual cost of production + supplier and distribution margin then pricing is starting to get to the point of being fully economic, for new cells..

Recycling used cells that still have plenty life left in them is a huge win for everyone if done right and the economics of using used cells, if they are cheap or free then this would make even subsidied electricity viable to compete against. Note "cheap"....

If you buy a solar panel at the current market price (wholesale rate) then your energy cost out of the panel is less than $0.02/kWh over the life of the panel. The down side is that if it costs $0.15/kWh to store that energy and release it again then this starts to be difficult to compete with, excluding any environmental consideration.

My belief is that using recycled cells for a powerwall is just as good in certain terms to planting a tree.....
 

cheamc

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completelycharged said:
If your country is subsidising the electricity then this does make your own power wall a difficult proposition. In the majority of other countries where the power cost is representative of the actual cost of production + supplier and distribution margin then pricing is starting to get to the point of being fully economic, for new cells..

Recycling used cells that still have plenty life left in them is a huge win for everyone if done right and the economics of using used cells, if they are cheap or free then this would make even subsidied electricity viable to compete against. Note "cheap"....

If you buy a solar panel at the current market price (wholesale rate) then your energy cost out of the panel is less than $0.02/kWh over the life of the panel. The down side is that if it costs $0.15/kWh to store that energy and release it again then this starts to be difficult to compete with, excluding any environmental consideration.

My belief is that using recycled cells for a powerwall is just as good in certain terms to planting a tree.....
My country is subsiding the energy as much as free for usage of not more than 200kwh/month. It mainly for the poor. With my average $0.06/kwh, it doesn't make sense to get into solar and powerbank.
Mainly as hobby/interest.
It is a joke in my country where produce 2nd or 3rd most solar panel in the world. We local have difficult to get a panel and the price is expensive.
But such subsidizing lead to people wasting the energyand resource, not creative and country development.
Getting a new cells here is so tricky where market is floating with fake China product. The recycle cell from the laptop is not cheap too. While people mostly using clone laptop battery that not sure what cell is inside.
 

completelycharged

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The economics for a powerwall with $0.06/kWh electricity cost would only make sense if it is to cover blackouts/loss of power and you value the lost power highly.

Solar could still work but if you end up exporting more than around 25% and do not get paid for it then it is not viable. Guessing you have a disc based electricity meter, which will spin backwards when exporting, so in theory, you could export the small amount and effectively reduce your bill. The economics at $0.06/kWh would take some time to recover your costs though.... more than 10 years..

That said I am also guessing the local utility would not allow this "if" they knew it was heppening.....
 

cheamc

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completelycharged said:
The economics for a powerwall with $0.06/kWh electricity cost would only make sense if it is to cover blackouts/loss of power and you value the lost power highly.

Solar could still work but if you end up exporting more than around 25% and do not get paid for it then it is not viable. Guessing you have a disc based electricity meter, which will spin backwards when exporting, so in theory, you could export the small amount and effectively reduce your bill. The economics at $0.06/kWh would take some time to recover your costs though.... more than 10 years..

That said I am also guessing the local utility would not allow this "if" they knew it was heppening.....

It is pretty efficient for energy supply here as average blackout occur once a year. At most twice. Only last 2-3hr. Which mostly happen during summer where people using aircon a lot.

In my calculation if you save the solar system investment money in the bank, the pay dividen is much more higher than the investment. Nothing to worry and maintainance free.We do have grid tie solar program. But it not profit anymore and more favor to solar farm. Blame the utility company monopoly.

Yes, it is illegal to supply energy back without proper authorities certified. For safety reason. I have done that before. It like reduce my bill most 7%/month.But as hobby/interest, that is nothing much to play around if put it into grid.

No matter how I calculate and reason, it is not economicsto invest on it. Can't paid back at all. Unless some drastic $/kWh up and solar equipment price cheaper.
 

Anannaki

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DarkRaven said:
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.

Could you share a link for such cells.
 
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This makes me realise that although i spent about 4-6 weeks looking for cells, i found 180 laptop packs brand new in boxes unopened with an average of about 7 cells per pack (some 6, some 9, so 1260 total cell, at 2300mah each) for 300gbp! A bargain...! (so less than 24p per cell!)
have had very few dead cells (maybe 7 in 100 as an average so far)...

i think i need to find more at this price! seems buying in bulk is the way to get deals, too many people on ebay are selling 10's or 20's of cells for way too much.

the time aspect hasn't really been much as testing i have just been swapping batteries in the morning/evening and charging/leaving, the thing that takes time is pack building more than testing IMO.
 
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