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Comment by jnsaff2 | Hacker News Reader

So estimating the lifetime of the battery at 5000 cycles and lets say round trip efficiency at 95% we end up with $0.082 / kWh. (EDIT: originally I claimed $0.074 which is wrong) that the battery adds.

So I'm guessing in the long run this will considerably lower the cost of electricity on the island as adding PV capacity is much cheaper than keeping a coal plant running and this battery allows to install much more and use the energy at night. Not sure whether Hawaii has much wind power but it would seem to be rather windy place.

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Can you explain your logic a bit more? I'm struggling to understand how you calculated the $0.074, and what you are saying it represents.

Edit: I suspect your calculations just represent depreciation over the batteries lifetime, which is only one of the costs involved.

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.

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

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.

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

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.

Typically at the moment we talk about a price of about $15 a MWH for Wind and $14 for Solar (last year anyway). So around $0.15 p/KWH for the power to charge and discharge it. Assuming the wind/solar is only going for a third of the day that brings the average price up to about $.209 p/kwh when we take into account battery wear cost. That is definitely economically viable in a very large number of places in the world.

Incidentally the totals work out about the same on a home solar system, my battery is 0.09 p/kwh and the Solar output averages out to about 0.07p/kwh but get paid for export at 0.15 p/kwh.

You misplaced a zero, $15/MWh is $0.015/kWh.

That's close to my guesstimates of about $0.10/kwr. So I tend to believe it.

The important thing is battery storage is competitive with peaking plants over a period of hours. And lowest cost when it comes to short term supplies on the order of seconds to an hour.

Also the logistics of containerized batteries is great. You need a place to put them and a grid connection. And nothing more than that.

Are you assuming zero cost for the power to charge the battery?

No. This is additional on top of energy production. Energy production cost was already in the base price quoted. The energy consumption will be roughly the same unless the price changes dramatically.

But this allows more PV generation to be put in which is the cheapest way of producing energy.

it won’t make any impact on the prices there because it’s a drop in the bucket compared to what they spend importing oil and diesel to burn for the majority of their electricity

rountrip is closer to 85% and you have to add the power electronic, also the graph is cell cost of module/pack/gigapack and security systems...

The windy side of Maui has a bunch of wind turbines.

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