A startup’s quest to store electricity in the ocean | Hacker News Reader

A startup’s quest to store electricity in the ocean

techcrunch.com

68 pointsrbanffy51 comments

It sounds quiet inefficient to me. The energy differential comes from the different salt concentrations, so you have to move a lot of water to exploit a relatively low mass differential.

Mentions of efficiency are conspicuously absent from the article.

Another potential problem is marine ecology: pumping high-salt sea water to the top and releasing it en masse might lead to much larger fluctuations in salt concentration than what the ecosystem is used to.

That said, we need many different approaches to solve energy storage, and I hope to be wrong, and that they end up very successful.

Yeah no mention of how it would effect marine ecology is bad, but the avg startup/mega-corp doenst care see how far people are trying to make deep sea mining legal, even with its obvious implications of destroying the sea

Uh, did you get the words mixed up? Perhaps "the avg person doesn't care see how far startup/mega-corps are trying to make deep sea morning legal"?

According to the article, both the reservoirs are sealed — the brine won't affect salinity in the surrounding water.

There's a pretty short video in the article from the company itself that answers all that.

From the article:

[Company] has tested a small model of the reservoirs in wave tanks and off the coast of Reggio Calabria, Italy. It’s now deploying a pilot of the floating components in advance of a full demonstration plant. By 2026, it’s hoping to deploy several commercial projects at sites around the world.

At full size, the turbines would generate around 6 to 7 megawatts of electricity each, and there will be one for every 100 meters of pipe. Deeper sites would have more storage potential, and each commercial site would host multiple reservoirs. Sizable hopes to deliver energy storage for €20 per kilowatt-hour (about $23), about one-tenth what a grid-scale battery costs. —-

Testing in calm reservoire is different from potentially .wild offshore (ocean/sea)

What happens to 100-200 m long pipe in underwater waves when e.g. a hurricane or a storm comes?

Even in a storm, just a few meters below the surface (half the wavelength), the sea will be calm.

The bigger issue with this idea is that it's a megastructure sitting in the ocean, and salt water turns everything it touches into shit. Oh, and there's very little energy storage potential from just a salt gradient. You need to move way more water, to get less energy, but your container costs are fixed.

Land-based pumped hydro has no shortage of engineering problems (and risks if, you know, you get a dam collapse), but this has colossal capex costs.

> What happens to 100-200 m long pipe in underwater waves when e.g. a hurricane or a storm comes?

Nothing, to a rounding error. The effects of surface storms are only noticeable to ~2x wave amplitude.

There are plenty of other forces at work, especially tides, but storms will only affect the surface plant.

What happens to 100-200 m long pipe in underwater waves when e.g. a hurricane or a storm comes?

That’s an excellent question, but it is also similar to asking what will happen to wind turbines in a storm.

Maybe some will break. Maybe that’s an acceptable outcome. Probably they can be improved to reduce that risk

This platform (from video in the article) seems fragile compared to wind turbines or oil rigging platforms.

I know that underwater is calm even during storm but happens to the top part that is connected with pipe to bottom part?

It's anchored to the seafloor. Also surely we have the technology to hold a pipe in high sea, as this is what petrol platforms are doing.

platforms are on stilts, no? Quite different from floating. But yea, seems doable.

There are floating platforms as well if the water is too deep for stilts.

ah! ty

Waves and weather can literally make concrete attached to rocky shores go flying... so one must not underestimate those forces.

My understanding of this technology is that it's closed-circuit. No water is exchanged between the power plant and the ocean once filled with ocean water.

To be honest, I find it a bit hard to understand even from the video. The top part doesn't look like it has any container at all.

right? really badly explained visually (no matter how visible the tanks are in reality)

I must have missed the video apparently...

What I don't understand is how the top reservoir is floating when filled with brine. Are the small floaters enough to hold it up?

Otherwise I love the fact that's simple. Simplicity scales. It's also salt water, so assuming they're not putting anything else than NaCl, it can break and it's no big deal

Have some air at the top of the top reservoir, assuming that the top reservoir is at most about 10 m deep in water (to avoid damage from storms). Or have the air in separate chambers fixed to the top reservoir.

Do I get this right?

- they concentrate salt water once to get "heavier than sea water" brine. Hope not chlorinated.

- it's then a closed system shuffling between bottom and top tank(s)

- everything floating is soft, so no strong forces unless a wave crashes on top

- advantage of ocean: "free standing" within height/depth margins, free water for initial fill

And really not visible in the video:

- the disk you see floating is a V shaped bladder with the storage in the V below surface and floatation sprinkled all around and segmented in to "cake wedges".

The maintenance on this will be a real killer and by the time you build the robotic infrastructure to maintain it you’re not a power company anymore kindof how Amazon isn’t a bookseller.

Wait a second $23/kWh? I pay ~ $0.15/kWh for power at my residence the majority of the year. Is this a proof of concept number? What am I not understanding such that the power this produces is 4 orders of magnitude more expensive than what’s in place currently?

kWh of capacity, as compared to a kWh of capacity on a battery, over the lifetime of the product.

On each of these kWh you'll have (hopefully) multiple orders of magnitude of charge cycles

I think they mean kWh of storage capacity – your talking about your energy costs which in a battery is the round-trip cost.

Battery capacity and energy consumption are measured in the same unit.

"An average lithium battery costs around $139 per kWh in 2024" - random result from first page of googling in ddg

https://www.renogy.com/blogs/buyers-guide/how-much-does-a-li...

It's like saying gas at the pump costs you $3/gallon but building a storage facility costs $100/gallon. Yes, they're both $/gallon, but these aren't the same measurements--one is for a gallon of dispensed gasoline and one is for constructing storage with the physical capacity of a gallon. One is the price of gas and the other is the price of storage. You can store and then dispense many, many gallons over the lifetime of that one-gallon storage.

How exactly are they pushing the brine against the ~50BAR pressure differential?

They're not dealing with a pressure differential. Or at least I don't think so.

I don't think the Journalist who wrote the article understood the technical details, but from digging a little at their website I think what's going on is they're moving heavy brine up and down, all of it equalized with local pressure.

Despite them describing it as pumped hydro, I think its better framed as a cousin of the "chunk of concrete suspended over a mine shaft" style gravity battery. Replace the mineshaft with water and the concrete with salt.

Oh, right thanks for clarification. They are indeed not pumping just any salt water, but much heavier brine (which they get who knows where).

So if there is any leak in the system, it will kill local wildlife right, like the brine pools under ice in Antarctica.

If there’s a catastrophic collapse, sure.

If there’s a leak? I don’t see why it would; the brine will be immediately diluted.

Relying on a salinity differential, even between salted and unsalted, seems like a terribly small amount of energy. There are projects to put large spheres at the feet of offshore windmills to pump water in and out. That has some pressure challenges but store a lot more.

The advantage I see for the salinity difference is that you can make them a lot larger than the pumped water ones. But is worth it, I'm skeptical.

Maybe I'm missing something but won't submerged structures like these get all covered in barnacles in a few months?

I don't think it is a problem for the outside shell, or maybe just a minor one. For the interior of the reservoirs, I guess the hyper salty water will kill everything that tries to grow there.

> Sizable’s reservoirs could connect to any grid that’s near waters that are at least 500 meters (1,640 feet) deep.

How many big cities are there on earth with that depth available nearby?

Could also be interesting in case the idea of under water data centers ever returns

https://en.wikipedia.org/wiki/Project_Natick

Or it could help offshore wind farms provide a more stable/predictable output.

It depends on the definition of "near", but there's a sizeable population within ~40km, which is a reasonable distance for an offshore wind-farm.

Almost the entire Mediterranean is >500m depth within just a few km of the shore, and that's half a billion people. All of the eastern seaboard of the North+South American continent is available at 100km distance (another 100-200mn people). Most of west Africa, all of Australia, and almost all of the western flank of the Pacific.

Maybe a quarter of all people live within 40-50km of a 500m deep sea. Definitely a large TAM.

80% round-trip efficiency sounds very good. What am I missing?

That to store enough energy with just haline gradient the reservoirs need to be enormous

And under water construction is expensive. And durable construction in a marine environment is challenging (and makes things more expensive).

That doesn't mean it's a bad idea but they are factors that add to the overall cost. 20$/kwh is very attractive of course. But that's also a number that e.g. CATL is chasing with sodium ion batteries. And they are going to be making those by the gwh/year from next month.

Whatever happened to the BYD Sodium ESS [1]? By 2024 they were already taking orders and building a something-something giga-actory

Fingers crossed for both CATL and BYD

[1] https://www.energy-storage.news/byd-launches-sodium-ion-grid...

It's in the ocean, which corrodes and destroys All.

I’ll stick with my freshwater fish tank. Fewer bobbit worms as well.

So they have to build megastructures that withstand 10-20 bars of pressure changes? I don't get it otherwise.

Is the salt NaCl?

This seems like it could mess up local weather by bringing up water of different temperatures if deployed at scale (and if not at scale, what's the point?).

> if deployed at scale (and if not at scale, what's the point?).

The "at scale"s might be very different between "what would be enough to affect local weather" and "what would store all the excess electricity generated in non-peak hours".

Whatever this is, leave the ocean alone unless this is beneficial to its inhabitants.

Should we not do the same on land too, since it's significantly more scarce than ocean?

This seems relatively non-invasive. It seems like the thing is closed-circuit, so there isn't even a brine / freshwater problem.

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