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Comment by bell-cot | Hacker News Reader

Idea: Convert a cargo ship into an Aluminum Smelter. Regularly relocate it to ports where the price of electricity is minimal or negative. Profit.

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Using excess electricity to generate hydrogen would be ideal,right?

A vote for underwater compressed air energy storage here. Simpler and less dangerous all round than hydrogen.

Underwater? I’ve heard of underground compressed air storage, but not underwater.

Big balloon tethered to sea floor. Pump air in when you've got spare energy, hydrostatic pressure forces air back out when needed. The neat bit is that the air pressure doesn't tail off as the bag empties. Site near offshore windfarms and you don't need much more infrastructure.

The main issue as I understand it is that you lose a lot of energy to heat if you just pump air straight in. To be efficient you need to chill the compressed air down to water temperature and store the heat before you pump the air underwater. Then add the heat back to the air when you release it from the balloon. This is all doable, but with all those heat pumps it's not quite as simple/cheap as it might seem.

Oh, that sounds really workable! And you can store more energy in a smaller space due to the water pressure I guess.

I suspect it helps with temperature regulation for the tanks.

Do you have a favourite resource to learn about UWCAES, please?

Not me, but I hope an SME will be along in a minute so we can both learn...

Transmission prices are a big chunk of the total per MWH cost even in times of normal prices. This is also why prices go negative in the first place, it costs money to use it.

I wonder what reasonable alternatives there are to fixed transmission prices. Though probably in times of high production, transmission would be more likely to be a bottleneck and priced even higher...

Or site big batteries at every unthrottleable power plant.

Check the prices. At the current prices, they won't pay for themselves. I did the math on a 100kWH and a 10kWh battery assuming 60 days of negative energy prices (5 hours per each such day) and even assuming you can charge them fully within that window, you won't recover their cost in the 10 years they are guaranteed to work. Not even 1/3rd of their price. With abundant energy during sunny and windy days in Northern Europe, investing in panels or batteries is questionable at this point. Chances are, your neighbours are already subsidizing your energy consumption.

What numbers did you use? How much cheaper would batteries need to become to be viable?

Pump water to a higher location.

A bit of a challenge in the Netherlands :-)

Not so hard… almost anywhere they pump to will be a higher location. The Atlantic Ocean, for example.

Do they use water towers for pressurising mains water in Netherlands?

Just be careful not to dump the waste chemicals…

You will need to pay for a whole lot of fuel.

And probably not get to the place in time.

In the NL, energy prices are settled a day earlier - at 3pm, if memory serves. That floating smelter needs to be quick.

To sail the ship around? I'd think the smelting operation would cover those costs.

We have Bitcoin for that.

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