Blog - Tests and diagnosis

20. Jan 2019
 
How to calculate the cost of stored energy in a LiFePO4 cell?

 

Lead Acid or LiFePO4? This is the price per kWh stored and cycle life comparison.

The two following graphs will show you the comparison between the Lead Acid and LiFePO4 batteries. The first one compares the average number of cycles (cycle life) according to the battery type and a depth of discharge. The second graph applies these figures to calculate the cost for one kWh of energy stored – again according to the battery type and the depth of discharge.

If you wonder how we got these figures or even would like to calculate the costs for a kWh stored for your own battery storage system, follow the steps below the graphs.

 

How did we get these numbers? Plus some basic terms definitions

> A 300Ah battery costs around 330€

> It has a voltage of 3.2V. The battery capacity in kWh is then:
3.2 * 300 = 960 Wh = 0.96 kWh ~ 1 kWh

> Because we want to gain the longest possible battery durability, we will use it only for 50% of the capacity (this is so-called 50% DoD – depth of discharge). The usable battery capacity is therefore 0.5 kWh.

> With this low DoD, the battery endures storing this amount of energy for about 10 000 times back and forth (= number of cycles = cycle life). Then it begins to degrade rapidly.

> Then, I calculate the total of energy stored over the battery durability:
10 000 cycles * 0.5 kWh = 5000 kWh = 5 MWh

> The cost of storage (or discharge) of 5000 kWh was 330 € = the price of the battery itself.

> Now I can get the cost for 1 kWh stored-and-discharged easily:
330/5000 = 0.07€

The cost of storing (or discharging) one kWh is 7 cents.

 

 

 

How to calculate the cost of stored energy in a LiFePO4 cell?


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