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Comment by lukev | Hacker News Reader

This is built in to wholesale energy markets and well understood. Energy prices go negative with some degree of regularity and it is built into the system.

If you already have a grid interconnection and a handy energy sink, you can definitely make money just buying excess power for a negative price at certain times. So far, though, it's not quite frequent or extreme enough to justify a bespoke infrastructure investment.

And if you're going to make some kind of investment, better to spend money on some kind of energy storage tech (i.e a chemical or physical battery.) Then you not only take excess power off the system when it isn't wanted, but also help power the evening peak when usage ramps up just as solar is ramping down.

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Iceland developed a aluminium-smelting industry to make use of the country’s plentiful (cheap) geothermal energy supply.

Except that aluminum smelting requires near constant power levels or the smelting pots will freeze and need to be replaced. So it's not really relevant here.

I was just on this https://www.youtube.com/watch?v=-Ss_wHCS1Aw

The smelteries use hydropower, and the power wasn't just laying around, each smeltery requires building a massive dedicated hydropower plant.

Fun fact: this is why the US aerospace industry grew up in the pacific northwest.

At the beginning of the 20th century we went on a bit of a dam building spree up there (and all over, but heavily up there). Then when WWII broke out and we got a huge demand for airplanes (which require light aluminum), the industry congregated around where there was an excess of cheap hydro. Hence Boeing, Lockheed, and friends all being out of Seattle.

How does one enter the market to buy negative priced energy? How much money could I make if I boiled off my swimming pool?

In the UK there is a provider than bills the "live" electricity price using smart meters, (in reality I think it's 30 min chunks but close enough). Sometimes at low demand and high wind and solar output prices go negative.

https://www.energy-stats.uk/octopus-agile-london/. I think the all time low was -10p/kWh. Most of the time it's around -3p though when it does go negative. Assuming you had a 20kW (massive) heater you'd only make maybe £1-5/day running it when the prices are negative, which isn't hugely often ATM. So probably not economical, yet.

I think some people with a pool would be totally fine, esp in colder months, using it as an energy sink, make it possibly more pleasant / usable.

The author mentioned just such an energy storage tech: water.

Water (pumped hydro) storage is really great, but only works well at scale where the geographic features support it.

the article mentioned desalinating water as a way to use negatively priced energy and storing the value in a commodity for sale or consumption at a later date, not pumped hydro storage

Stored water for hydro power generation is also a commodity for later sale or consumption.

Existing hydro (not pumped) also acts as storage: a decrease in the load on a normal hydro dam means more stored power... and all the infrastructure exists including grid connection.

It a lot of cases that doesn't happen. The water levels in the headwaters and the amount of flow on the downstream river are controlled with goals other than power production. Like not causing floods, and having enough water depth for navigation. In Ontario, Canada, if the plant doesn't run at capacity, generally the water is sent through the spillway without generating power. I'd assume that to be common in many hydro-electric installations.

To be fair, they didn't really mention water as a battery. Yes, they used the phrase "bottled electricity", but that was in reference to the large energy cost of desalination. You can't then get the energy back out like you could with an elevated lake.

but you can schedule large swathes of energy intensive industries that don't rely on human fingers so that they happen at cheap power and no longer happen at expensive power.

humans don't desalinate water with their bare hands...

The problem with water is that to make it cost-effective requires appropriate geologic configuration and massive infrastructure investment. In California for example, all the appropriate locations are used, there are no more viable locations (according to the USGS)

What about electric water heaters? I am unfamiliar with the usage patterns and losses over time, but having my home water heater having some variability in temperature would be ok with me — I’d simply adjust the handle in the shower.

Colleagues of mine are working on a system using these kinds of water heaters. Specifically, they are working for a standardized protocol to allow these devices to negotiate prices / indicate to the grid how much they could take.

From what I heard they said something like a half-time for the heat in these devices of about 1 to 2 days.

Could do the same with freezers. And maybe a few degrees with fridges.

And boost those with phase-change materials at the right thaw points.

With a properly installed thermostatic mixing valve, you don't even need that. The water will always exit at a safe, constant-ish temperature regardless of the water temperature in the heater, by mixing in the cold supply.

Interesting idea. It'd have to be done carefully because there are problems with going too cold or too hot:

* Too cold: Legionnaire's disease. Presumably not right away, so maybe there's some wiggle room if you're careful about timing.

* Too hot: scalding, particularly if you have kids. Maybe a new design could have a thermostatic valve on the output to give more flexibility.

Thermostatic valves are common in institutional water heating installations.

There are also quite a few people who use thermal storage with wood fired boilers. The boilers burn the most efficient and cleanest when they are near full output, then hot water is stored in an insulated tank to intermittently supply the house with heat.

Description of one such system: https://www.newhorizoncorp.com/PDF/ekomanual.pdf

You can't build pumped hydro storage. You can only "discover" suitable sites.

Yeah, I was surprised by the OP’s assertion that energy prices never go negative. I think spot prices have been negative in eg Texas on windy (and maybe also sunny) days.

They have gone negative briefly in Germany, as well. Both still rare occurrences at this point, though.

Due to issues with transferring energy, German producers will often pay Netherlands ones to shutdown their windfarms and export electricity there.

Briefly? It's very common. Even UK _retail_ energy prices go negative a fair bit. https://www.energy-stats.uk/octopus-agile-london/

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