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Comment by tinco | Hacker News Reader

Not sceptical of the achievement which no doubt was a small feat. But is desalination and purification something that's been a blocker for electrolysis? I don't remember ever even seeing this in efficiency charts of for example hydrogen powered cars. Maybe I always glanced over it, but I just assumed there is always plenty fresh water available for hydrolysis, no need to even consider sea water?

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There is no fresh watter at sea wind generator fields.

Nice, that's a cool scenario I hadn't thought of. I haven't heard of any deep sea wind generators, but obviously that might have great yields. I wonder if that far out at sea it wouldn't be easier/more feasible to have solar panels instead of wind mills.

Tidal turbines are a good contender. The tides are constant.

As someone who has spent a fair bit of time in / around salt water I’m skeptical of these claims. I want to see all in deployment costs with maintenance. Are these deep water or do they need to be shallow water where they will be banged up even more in storms etc

I don't know about tidal forces, I do know in the Netherlands they create energy from salt / fresh water dialysis. https://redstack.nl/en/

Tidal turbines are viable in inlets where currents are consistently strong during tidal changes, the problem is they often disrupt the ecosystems around where fish need to spawn. Altering the total water flow into estuaries is sketchy and the good places are typically shipping lanes. You could put them in a place like Gibraltar and live with reduced water exchange in the Mediterranean, but it will be met with a lot of resistance.

Ideas that rely on moving a mass up and down 10 feet every 6 hours require floating platforms the size of Rhode Island. Not cheap to build.

Neither strategy is a contender in my book. I recall a research project in France which the results were unappealing. The environmental costs were high and power generated was low. You have to be careful getting scientific knowledge from the mainstream press or researchers who need to sell their research which means it is more akin to marketing than scientific knowledge.

Attempts at tidal power extraction in the Bay of Fundy have failed because the turbines broke, every time.

Attaching a simple float to a cable and pulley turning a generator onshore seems not to have occurred to them.

Numerous (i.e. all) wave energy startups have likewise gone bust trying to keep machinery working exposed to maritime weather. It seems never to occur to them to keep the stuff that would need attention onshore and indoors.

Using [1] temperature difference between deep water and surface water may be even more efficient

[1] https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_convers...

You can bypass the heat engine, and just condense humidity onto coils with cold deep water running through them. You only need an insulated pipe to bring the deep water up through. The more water you move, the less insulation you need.

Offshore wind is proven tech at this point, to the point that there are commercial offshore wind farms that have been built without any subsidies. Mainly in Europe but starting also in the US. There is no major R&D necessary to make it happen, just scaling and cost engineering.

The Biden administration target for 2030 is to have 30 GW installed generation capacity in offshore wind.

Yeah but none so far away that you couldn't just lay a cable to transmit the power to the shore.

> Offshore wind is proven tech at this point

Shallow water only. The North Sea is perfect, the east coast of the US looks good in places. Deep water is unproven currently and in the R&D stage with no known economically viable solutions.

Major construction projects are ongoing, based on already proven solutions.

Bullshit. Best so far is Hywind, which is 3x the cost per MWh of shallow offshore.

There is also https://en.wikipedia.org/wiki/Wave_power

Its easier to lay an electric cable to shore than to build a hydrogen plant at the sea, deal with corrosion, move hubdreds of staff there every day by boat and canisters of pressurised hydrogen.

I am not seeing the practicality of this outside of some really niche areas.

Desalination produces extremely concentrated brine as a waste product. Dumping that brine into coastal waters can kill a lot of marine life, so I imagine keeping the plant offshore helps.

The current way the waste is handled is by laying a pipe from the shore deep underwater away from the coast. The brine is diluted with fresh seawater and pumped all the way down.

By having the plant offshore, drawing in fresh water to dilute the waste becomes cheaper, and it's cheaper to build a vertical pipe to discharge the waste deep underwater.

There's other byproducts like chlorine gas and sodium compounds released from cracking salt molecules. Small amounts, but keeping that offshore is a plus in my opinion.

why do you need desalination, you only need a small amount of fresh water for electrolysis. Any standard city water supply will power a very large electrolysis setup.

Also you seem to be massively underestimating the effect of corrosion, and needing to transport stafff and eqipment back and forth offshore

Tbh I got myself a bit mixed up. Desalination and hydrogen electrolysis have similar problems.

Brine waste is still a problem with electrolysis. Everything that isn't water is left behind, and must be disposed of. Some of the dissolved gases and ions also get liberated, but in fairly small quantities.

The article in question is about seawater electrolysis, and my understanding is that the dissolved ions in the water should improve efficiency (though I'm no expert).

As far as corrosion, you're vastly overestimating the problem. We've been dealing with salt water corrosion for at least the last century. It isn't that bad if you keep up with maintenance.

I used to work in the marine coatings industry, and the technology today is incredible. With a properly maintained coating and sacrificial anodes maintained regularly, corrosion damage is minimal. After all, we have countless steel cargo ships and oil rigs on the water today. A quick Google suggests that the lifespan of a cargo ship is on the order of 15-40 years. USS Olympia is a steel hull ship that's been in the water since 1945, and she seems to be doing fine.

Salt water corrosion is a problem we know how to deal with, all it requires is regular maintenance.

The cost of a good marine coating for something the size of an oil rig would be a couple hundred thousand dollars, and will last many years with regular maintenance.

And as far as ferrying crew to the rig, the ferry from Seattle to Southworth costs about a million dollars a year, running 8 hours a day, ferrying up to 2400 people a day across 9 miles [0]. Extrapolate that to two or three round trips a day and you're down to a few hundred thousand dollars a year. Since the ferry is going to what is effectively a power station, it could even be powered electrically, which would further drive down the cost.

Realistically, we've been building and manning offshore platforms for a very long time. Oil rigs don't rust out and collapse into the ocean. Cargo ships don't fall apart unexpectedly. We have a lot of steel floating in the ocean with no problems, as long as they are maintained.

Yes, there are problems building structures in hostile environments. But we've been doing it for a very long time, and most of these problems have solutions.

[0] https://leg.wa.gov/JTC/Documents/POFCostAnalysis.pdf

Yes, exactly this. These membranes will foul and need replacing. I don’t see why anyone would use this over freshwater. There’s plenty of freshwater available in many places. It literally runs into the ocean. You just don’t build one of these plants in the desert. It might be interesting in niche cases - desert countries where they're already producing water via desalination. But those countries tend to produce energy from fossil fuels anyway, and it's less effective to burn fossil fuels to split water than it is to just split methane to begin with. Maybe in the far future.

> You just don’t build one of these plants in the desert.

If you're generating the electricity in a big solar field which would ideally be built in a desert (few clouds, cheap land) then building the electrolysis plant nearby makes sense. There are lots of areas like north Africa, western Australia, the southwest of North America, the Arabian peninsula, etc where sunlight and sea water are readily available but fresh water is at a premium. Ultra high voltage DC makes power transmission over continental scales technically possible, but the losses are still significant, having the option to use power close to where it is produced enables a lot of possibilities.

In Arabia and North Africa it makes more sense to use the solar to displace fossil fuel derived energy than to produce hydrogen - again if you want hydrogen and you’re burning fossil fuels for electricity it makes no sense to use the electricity to get the hydrogen - use methane and cut out the middleman.

There might be some places where this could work, but they do seem quite niche.

You can both provide power locally (if needed - the desert regions with little rain and cheap land tend to have minimal population) and also produce hydrogen with excess power, which could be exported to other locations, used locally as an alternative to other energy storage methods like batteries, and for various things which are not trivially electrified like industrial process heat or vehicle fuel.

No one here is arguing that fossil fuels should be burned to conserve solar energy for other uses.

Excess power would have to be very sporadic, too sporadic to offset fossil fuel generation - in which case it’s too sporadic to justify capital expenditure for electrolysis and hydrogen production. I just don’t see it.

Even fresh water needs to be filtered before running it through the electrolysis. But yes, part of the problem with electrolysis is the power cost compared to current "blue" hydrogen, which is decarbonated natural gas. Some of the better places to get electricity though have been places with little fresh water, so being able use saltwater instead helps with this idea.

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