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Comment by jnsaff2 | Hacker News Reader

The capacity of the battery is 565 MWh.

The cycle life of these kinds of batteries is about 5000. Meaning they get about 5000 charge and discharge cycles before their useful life is over. It could be 2000 it could be 10000 and the definition of useful is also dependent on application.

So in it's lifetime this battery can store 5000 * 565 = 2825000 MWh

The cost of the system was $219M.

About 5% of energy is going lost due to inefficiencies.

$219M / (5000 * 565 * 0.95) = $81.6/MWh = $0.082 / kWh.

I am sorry for calculating the efficiency incorrectly in the original post.

This does not take into account the maintenance cost.

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Unless these are special a "useful life" rating of 5000 cycles mean that after 5000 cycles your battery will be down to about 80% capacity compared to their original MWh rating.

But full cycle is probably not the complete picture when it comes to grid scale storage since they have some control over the charge/discharge rate and they can optimize their usage, a bit like how electric cars allow you to stay in the 20-80% range instead of going all the way up to 100%.

Good point. In 0% to 100% capacity cycle, the battery will be dead long before 5000 cycles. OTOH, listed capacity may already take into account a more gentle 20% to 80%, or less, cycle. https://www.tesla.com/megapack doesn't provide specs, though.

Thanks! No need to apologise, it's fun to run the numbers.

On top of maintenance costs we probably need to account for finance costs (5% interest rate means repayments of 100mil over 10 years) and the fact batteries don't tend to ever get charged/discharged 100%.

Presumably if you built this you'd want a bit of return on your investment, so you'd have to charge more on top.

TBC: I think these batteries make economic sense (even more so if coal/petrol had externalities baked into their costs), but we don't want to oversell things

At least in theory it should be possible to recondition these batteries to make them useful again, I'm not sure who/when/how much but I suspect they will never be completely worthless.

I wonder how much the one-time costs were for this project, compared to the cost of the batteries themselves:

- land acquisition

- earthworks

- civil construction

- grid hookup

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