#### completelycharged

##### Well-known member

- Joined
- Mar 7, 2018

- Messages
- 1,053

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 ?