Process to Produce Hydrogen from Water Using Sunlight Reaches 16.2% Efficiency, on Its Way to Meeting DOE Target

It is not being proposed as a source of energy.

You could do the same yourself.

The first link is /not/ about electrolysis - which is the use of electricity to split molecules (often water, but not just that). No one thinks that is a source of energy.

The first link is actually about using solar power as the source of energy to split the water - this is, of course, an excellent idea (assuming the economics of making the plant are reasonable). Hydrogen is a very flexible and energy rich base which can be transported around and provides clean energy. (It is not the /source/ of the energy, but the transport for the energy.) It is not perfect for every use, of course, but it /is/ useful - and if it were available cheaply, we'd see a good deal more use of it.

The second link is about combing hydrogen with atmospheric CO? to make hydrocarbons - clearly, a "clean" method of producing petrol would be an ideal way to re-use existing cars and infrastructures in an environmentally friendly way. The article does say they are making the hydrogen by electrolysis - but the power source is hydroelectric. No one suggests the electrolysis is the energy source. And if there is a cheaper clean source of hydrogen - such as producing it directly with sunlight - then they would use that.

Algae or bacteria (probably genetically modified for the job) would be much more efficient to grow and process, and can be grown in places where food cannot.

However, biological photosynthesis is between 0.1% and 2% efficiency for converting solar energy to chemical energy - far, far below solar panels or this STH technology. And most of the plant's energy goes to plant growth and plant life, rather than being stored as usable oil. Even for the best oil-producing plants, STH and solar panels are two orders of magnitude more efficient. And when you take into account the energy needed for processing the oil, for collecting it, for planting it, for the tractors, the fertilizers, the people working at it, I would expect it to be a significant net /loss/.

Alternatively, find an area of water that doesn't have force 10 gales.

If we don't do something like this, there will be plenty of areas of water to use - they will be where your cities used to lie.

According to the infallible google, an offshore 3 MW turbine typically produces about 6000 MWh per year (since 3 MW is the peak, not the average).

That works out to about 24,000 windmills for the oil rig.

Of course, the windmill output is electricity - the oil rig output needs to be processed in all sorts of ways, and transported around, which greatly reduces the efficiency.

Still, there is a reason we still use oil pulled up from rigs and don't rely on wind power alone, as these numbers show.

The USA DoE's target of 25% efficiency is, obviously, totally arbitrary. It's just an aim. In reality it all comes down to the cost of the making the cells compared to the value of the generated hydrogen - if the devices are cheap enough, people will make and use them at 2.5% efficiency just as happily as a 25% efficient system at ten times the cost. You need high solar efficiency if you are putting these things on your roof or other places where space is a premium - if you are using a desert with plenty of space and sunlight, it really doesn't matter. Only output-to-investment efficiency matters.

You can do it on land, but the point in view is the difficulty of using the vast empty areas of ocean.

Cheers

Phil Hobbs

Except that they'd wind up on beaches on a large scale.

Cheers

Phil Hobbs

Right, but if you forget about harvesting, maybe we could use the empty oceans for carbon capture. Probably some critters would discover the algae food source and eat it.

George H,

Or we'd discover that the transgenetic critters produce something that poisons the whole oceanic food chain.

Cheers

Phil Hobbs

The link was about scrubbing CO2 from the atmosphere, combining that with hydrogen obtained via electrolysis to produce fuel.

If you don't think that's crazy, then sorry, but you are beyond help.

OK, they don't mention where the electricity to obtain the H2 is coming from. That makes it worse, not better.

Jeroen Belleman

Please re-read what I wrote, and think about it rather than being so keen on calling people and ideas "crazy".

Note that I have no idea how economical or efficient this whole idea is

- I will reserve judgement on its "craziness" until I know that.

As a general point, we are getting steady improvement of the availability of cheap clean energy. But that energy is often most efficiently produced in a place where it is least practical for immediate use - solar energy in a desert, wind energy out at sea, etc. And converting users of dirty energy sources - primarily oil products - into users of clean energy is difficult, expensive, and loses convenience. Therefore it makes sense to make clean energy somewhere that has plentiful supplies, and turn it into practical alternatives to fossil fuels. You keep the convenience of oil-based energy, but stop killing the planet.

So the principle here is far from crazy - it is an excellent idea. But the /practice/ of it depends on the efficiencies. Pulling CO? out the atmosphere will take energy, and that could easily be the killer here. (The electrolysis for generating the hydrogen is a minor point.) And it would all need to be done on a massive scale to be helpful.

I suspect in the future the shallow sea will be built in/on, as the value of land for building rises & the cost of moving rocks falls. Whether it would make sense to build so as to enclose new saltwater lakes who knows.

NT

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that's what completely crazy about it. It's just a way to throw away energy & money.

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It's a complete nonstarter from energy & money povs.

NT

It's economically viable when/if a carbon tax supports it, but that's not the same as crazy.

Whoa! The original post wasn't about electricity making H2, it was about sunlight making H2.

In other discussions, we find that many sources of electricity produce excess at odd times, and that excess is an opportunity to consider. A nuclear plant, for instance, can operate effectively at full capacity 24/7 with only minor (fuel) costs, IF there is a useful local sink for its extra electric output. Making hydrocarbons out of pollutants sounds useful.

There's nothing crazy, nor extra-crazy, where you're pointing.

If the energy is free where is the cost?

seems like a good use for excess energy

production", basically a solar cell dipped in water. The circuit is short, but it's still electricity making H2, even if the electricity comes from sunlight. Good luck in making that contraption economically viable.

Carbon tax distorts the economy, driving it away from its natural optimum. It may serve to drive the economy towards a different optimum state, if such exists. That may be useful, but it should be temporary because otherwise it would just be throwing away money.

Jeroen Belleman

There is no such thing as free energy. There is always a cost associated with turning it into something useful.

For decennia, the gas that came up with oil was thrown away. It was 'free energy', but turning it into something useful was too expensive. That's gradually getting better, at long last. But this was a *concentrated* energy source, much better than wind and sunlight. And it was wasted nevertheless! Economy at work.

Scrubbing CO2 from the air and turning it into fuel will always be a nett waste.

Jeroen Belleman

Not if it supports agriculture, fisheries, and the heritage of natural wildlife. It's a cost of preserving a livable environment for our descendants, a long-term investment.

By some estimates, it can reverse the CO2 trend for less than the cost of a war, and ignoring the problem isn't l ikely to be cheaper than that.

Aztec cities buried in jungle growth prove a civilization can be felled by overexploiting a resource.

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excess at odd times, and that excess is an opportunity to consider. A nuc lear plant, for instance, can operate effectively at full capacity 24/7 wit h only minor (fuel) costs, IF there is a useful local sink for its extra el ectric output. Making hydrocarbons out of pollutants sounds useful.

Not strictly accurate. A carbon tax ought to recover the cost imposed on th e economy as a whole of the "externality" of dumping extra CO2 into the atm osphere.

Because the current economic arrangements ignore that cost, they are sub-op timum.

When you talk about "optimising the economy" you need to think carefully ab out precisely what economy you are optimising, and over what kind of time-s cale.

More CO2 in the atmosphere is eventually going to let the Greenland and Wes t Antarctic ice caps slide of into the sea and produce some ten metres of s ea-level rise, devaluing a lot of expensive shore-front property.

This isn't the only incidental cost, but it is a fairly obvious one.

Submerging the sea front of every coastal city wouldn't be throwing away mo ney?