Hacker News Reader

Comment by bit_logic | Hacker News Reader

Every time there’s a discussion about synthetic carbon fuels, there’s the same frustrating replies. I want to reply to those with one statement: the whole point is to use excess power from solar/wind. There’s always the same replies pointing out how it’s more efficient to use the power directly in EV batteries, laws of thermodynamics, and other similar things. Those completely miss the point. Solar/wind is going exponential and we have a big problem of storing excess power. Massive really massive amounts of batteries is one option. But converting that into carbon fuels that work directly in existing infrastructure and is effectively carbon neutral is a good option too. That’s where the discussion should be, not pointless arguments about efficiency of EVs.

View on HN

A problem with processes based on using excess power is that they use equipment inefficiently. If cheap power is only available for a quarter of the time then it would take 4x as long to pay for the investment in the equipment. Whatever scheme you set up to use excess power needs to be pretty cheap to make it worth running only a small part of the time, or it needs to be doing something especially valuable.

Compare to the strategy of locating somewhere that electricity is always cheap and running all the time.

Solar produces only during the day, but wind is at any hour. And these days, the idea of massive over-provisioning is being discussed to overcome the intermittent problem since solar/wind keeps getting cheaper and cheaper. The idea is simple, how to overcome the cloudy winter day issue? Simply overbuild a lot of solar/wind so it can still provide enough on a winter day. Then during summer, shutoff the excess power generation.

But what a waste of potential to do that! All that overbuilt power generation, simply turned off during summer. Batteries don't help here, it would store it, but then the question of what to do with it is still here.

If society goes the route of massive overbuilding solar/wind, then there's an opportunity to do something with effectively free power during summer. But it's ONLY during summer, so it needs to be something valuable that can also act as a energy storage.

Carbon fuel is perfect for this. Millions of ICE cars exist and are still being produced. Long distance airplanes will be carbon fuel based for a long time. And so many other uses. I think another option is water. Water can also be seen as a valuable resource that acts as energy storage. Use the excess summer power to fill up a near empty dam with desalinated water? Sounds like a perfect fit for regions like southern California or Arizona.

Oh, but look at the equipment that's shut down, doing nothing, all winter! What a waste. Sure, the electricity is a bit more expensive, but it's still fairly cheap so why not turn it on and get some use out of it?

All processes have some waste. In the end, you need estimates done with real numbers to see if it's worth doing. We aren't going to settle it with casual chit-chat.

>Use the excess summer power to fill up a near empty dam with desalinated water?

Pumped storage hydroelectricity is the biggest form of power storage at the moment, and has efficiencies around 70-80%. The losses for desalinization (pumping through media) are ruinous compared to just pumping uphill, and storing desalinized water means you can't use it without spending potential power. There might be good reasons not to mix desalinization and energy storage.

As I understand it, the main challenge with pumped storage is that you can't do it everywhere. You need fairly specific geography for it, and it's a big civil engineering project. Here's a good video on by Practical Engineering:

https://youtu.be/66YRCjkxIcg

Good video, thanks. It briefly mentions the idea of pumped seawater storage. Is that really any different from using freshwater, other than location?

I imagine the main difference would be salt content, but I can't speak to how that would affect things.

seawater is saline, you have to be careful what you do with it because you dont want to literally salt the earth where you are (soil remediation friggin sucks).

seawater is also not valuable. You don't care about the water quality in the reservoir, you just let it fall back into the sea. If it evaporates you're losing energy but you aren't losing potable water that you sell, and it doesn't require a connection to a water distribution main.

> You need fairly specific geography for it, and it's a big civil engineering project.

You need elevation difference and fairly stable soil. Everything else is technologically solveable. It's a big civil engineering project but its a profitable one and not particularly challenging.

I think the idea here was simply to use the excess energy to stock up on potable water, which people could drink later, rather than to also use it for pumped storage.

> I think the idea here was simply to use the excess energy to stock up on potable water, which people could drink later, rather than to also use it for pumped storage.

If it was a reasonable and profitable use of energy we would already be doing it, but we're not because its ruinously expensive. You also run into storage issues (how much of your excess power is being evaporated from the surface of your storage reservoir? The longer you hold your potable water the more you throw away). You also need to consider what you're going to do with the highly saline byproduct of any such process.

There's nothing wrong with purifying water but its very energy intensive and already something we do. Adding more expensive potable water from excess energy generation doesn't make much sense.

One issue with carbon fuel is air pollution, we have seen during the pandemic that getting people out of cars is a big part of solving that.

Re water, in addition to filling dams with desalinated drinking water we could also refill aquifers that are being emptied by overconsumption of water (often leading to intrusion of saline water into the water table and associated problems).

If BEVs capture even a fraction of the market then you've effectively a massive distributed battery which could help soak up the excess renewable electricity. Quick estimate - if 1% of the US passenger vehicles were BEV each with 50KWh batteries on average is 100GWh of storage.

It would require dynamic pricing to the consumer to work as off-peak prices would need to be low or very low to encourage all BEV owners to take on the excess power at particular times of the day.

By the way, unfortunately dynamic pricing seems to be a very unpopular idea as far as I can see.

Yes, you can't do your price calculations based on 24/7 utilisation. But that's true for almost every other bit of technology as well. What's the average utilisation of a theatre? Of a plough?

> the whole point is to use excess power from solar/wind.

Thank you.

> But converting that into carbon fuels that work directly in existing infrastructure and is effectively carbon neutral is a good option too.

This approach seems really underrated, at least for transportation.

Hydrocarbons still have the best energy density of the realistic options. We have a century of experience building ICEs with favorable power/weight ratios. Why throw all that away?

Too often have environmentalists let the perfect be the enemy of good. I understand why they feel that way, for so long have they fought against fossil fuel companies and other interests. They feel like if they give an inch, they will take a mile and climate change is too urgent. And so they oppose any transitional technology. They want to push for only perfect solutions like EVs and batteries.

But I want those environmentalists to sit down and think. Yes, climate change is urgent, and that urgency should make you stop asking for perfection. There are 1.4 billion cars in the world. Even a 100% ban today on ICE car production is not going to change that. Cars have an average usable span measured in decades. The projections for 2050 are catastrophic if carbon emissions don't go down.

Green tech has one big overwhelming victory right now, solar/wind. It's annihilating coal and will eventually defeat natural gas as well. We can take that victory and use it to make the existing cars and airplanes carbon neutral. If you care about climate change, why is this not more exciting than EVs?

Well, is it such a big victory for renewable? I think the big winner atm. is natural gas from fracking, which could easily be the final nail in the coffin.

What's missing is a careful differentiation between doing what you said, storing excess energy, and approaches that are popularized, e.g. by carmakers unwilling to invest in R&D, where we keep on relying on hydrocarbons for things like transportation and heating and magically replace them with carbon neutral alternatives.

The first approach of using hydrocarbons as an energy buffer makes perfect ecological and economical sense and is most likely strictly necessary for a carbon neutral energy grid (barring battery breakthroughs), once we reach 60-70% renewable energy in our grids.

The latter approach however makes no sense at all, because we simply don't have enough space for wind and solar to feed our thirst for hydrocarbons with renewable power. The energy losses, both in the step creating the fuel, and in the step turning fuel to useful work, are just too great to fuel every car or heat every home in the world like that.

How big are the losses to make such a big impact as to say there is not enough space for enough solar/sun farms?

99% or what?

I think you're overestimating the amount of space we have realistically available for renewable energy. At some point I did the math for Germany.

The average German needs around 144sqm of solar panels (located in Germany) to meet their primary energy demand of around 48MWh per year (taking into account average production of solar panels in Germany). Germany has a population density of around 4300sqm / person. So in the ideal case with no storage losses you need to cover more than 3% of Germany with solar panels if you want to meet primary energy demand with solar power. (Wind energy is slightly more dense in Germany, but I haven't done the math there).

Realistically you might get something like 1% of the land area without huge resistance of the local population. Probably less, which is why offshore wind is popular. 100% renewable generation is only realistic because you can safely assume that large parts of the primary energy consumption are wasted. For example internal combustion engines are at best 40% efficient. Burning things for heating also only gets you 1J of heating per Joule expended, whereas heat pumps get you 2-3J. You just can't get away with losing another factor two to generate syngas, or even more if you want liquid fuels.

Of course you can justify some inefficiencies if you're willing to transport energy from far away (say solar power from the Sahara), but that is ridiculously expensive compared to more local generation.

> we simply don't have enough space for wind and solar to feed our thirst for hydrocarbons with renewable power.

I'm not sure if this is the case or not. To give some numbers:

Current global oil consumption is 54225 TWh, or 6.2TW [1] Current global solar panel generation capacity is 628 GW (2019) [2]. Median capacity factor maybe 25% [3] Current global wind power capacity is 650 GW [4]. Median capacity factor maybe ~37% [5]

Other renewables are unlikely to achieve the same growth as wind and solar, so can be ignored.

So we need to install 15x current renewables, times whatever the hydrocarbon creation process efficiency is, to produce all our annual oil demand.

Assuming a 50% process efficiency, we'd need to install 30x what we have now. That's a big installation, but it's not outside the realms of possibility. There's a lot of untouched desert in the world.

[1]: https://ourworldindata.org/grapher/oil-consumption-by-region... [2]: https://en.wikipedia.org/wiki/Solar_power_by_country [3]: https://emp.lbl.gov/pv-capacity-factors [4]: https://wwindea.org/blog/category/statistics/ [5]: https://energynumbers.info/uk-offshore-wind-capacity-factors

Thanks for doing the math. On a global scale it does look better than the math I did for Germany.

However, I think 50% process efficiency is too high. High temperature electrolysis is about 60% efficient, but then you only have hot uncompressed hydrogen. There are a number more steps involved to get to a liquid fuel, each of them with considerable losses. I can't find the sources right now but I believe I remember something like 15% end-to-end efficiency for getting to something you can fuel your car with.

Yeah, it probably is. There's not really a nice process for making liquid fuel - hydrogen isn't a great fuel really. My understanding is that the biggest problem with making a practical liquid fuel is ironically getting the carbon. Hydrogen is in water, but carbon is only really in carbon dioxide - which is at very low atmospheric concentrations and so takes an incredible amount of energy to capture.

Ammonia would be easier (ubiquitous nitrogen everywhere), but isn't a particularly nice fuel either. At least it's easier to store than hydrogen.

Bucky Fuller had the idea to just connect the world's electricity grids together. He called it "World Grid" I think.

That’s more efficient, but difficult politically and logistically.

How would that be more efficient? The transmission loss would be outrageous between the summer and winter hemispheres. Compare that with transmission loss for LNG tankers at the moment, effectively 0 even with the occasional leak in transit.

1) The main loss for LNG wouldn’t be transit, it would be efficiency during synthesis.

2) Any inefficiency during transit of LNG isn’t leaks, it’s the fuel burnt moving it around.

3) The cost of building high efficiency LNG power plants wherever you need power is another cost that should be considered.

Geography may also be a problem. Running a gigawatt cable from sun-soaked Australia anywhere in SEA is enormously expensive. Instead, packaging the energy into carbohydrates produced from waste water (cleaning it in the process) and waste CO₂ may be much more economical and convenient. You can likely produce the best quality Jet A fuel or octane 98 gasoline with little other fractions by tuning the synthesis process (unlike an oil well which gives you a mix you can't control).

Beside that, a transatlantic jet, let alone a Falcon 9, won't ever fly with battery power. You still need highly energetic fuels where power density is at a huge premium.

Not even power density but also the ability to get lighter as you go farther.

The need to fly commercial liquid-fuel planes beyond the near/medium future far from certain. To my understanding we could quite easily use electric ships for most trans-oceanic cargo, and supplement it with some rail tunnels/bridges crossing from the UK, over the Faroe Islands, to Iceland, Greenland, Baffin Island, and Québec. The only tectonic "issue" would be crossing the Mid-Atlantic Ridge on Iceland.

Sure, it'd be quite a large civil engineering feat, but the speeds would be hard to beat. It'd be just a 12h ride from London to NYC, assuming TGV's top speed of 575 km/h.

A potential alternative could be to use a low-flying plane and deploy a series of HVDC-fed buoys/platforms straight across the Atlantic for fast-charging.

You're right about the Falcon 9 though.

The article provokes these replies by prominently making this absurdly stupid statement:

This technology could be retrofitted to coal fired power plants.

No, it can't! The power plant is run precisely when you don't have excess power to store. Conversely, you don't have concentrated CO2 when the power is available. It might work for a cement kiln, but not for a power plant.

I'm sure you know that. But the idiot who put a picture of cooling towers into the article clearly doesn't. He probably doesn't know the first law of thermodynamics, either.

> The power plant is run precisely when you don't have excess power to store. Conversely, you don't have concentrated CO2 when the power is available.

Unless you have some way of buffering the CO2. Biologically, this is what CAM photosynthesis does [1], and i have a vague memory of there being an industrial equivalent. Something like dissolving the CO2 in calcium hydroxide, to make calcium carbonate, then later on sparging it with hydrogen to recover the carbon?

[1] https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism

I was sort-of hoping for this comment. What it boils down to is, what is easier? Storing hydrogen, or storing both CO2 and a hydrocarbon, or is there another way? With lots of caveats, because the chemistry isn't exactly the same. (I think there is another way, and it's ammonia and/or hydrazine.)

> Something like dissolving the CO2 in calcium hydroxide

That's terrible. Calcium carbonate needs to high heat to release CO2. Unless you want to leave CaCO3 well alone (that's the enhanced weathering concept), this is approximately the last compound you want to make. Simply storing liquid CO2 under pressure (80 bar or so? not nice, but doable) sounds much more appealing. (Ammonia is better in every respect, though.)

By golly, I agree! And I would agree even if I wasn't working on technology to achieve this.

Unfortunately, the article does not say how the zinc oxide nanoparticles will help with being able to use solar/wind power to produce syngas.

In fact it is not clear how these nanoparticles could actually be used to make an industrial catalyst. Current catalysts also use nanoparticles - on a substrate with enormous surface area/volume ratio, but these nanoparticles are created on that substrate.

I am curious about what the researchers plan as the next step.

Yes, it's worth making use of the excess power. The Orkney islands, for example, are using their excess wind and tidal power to produce hydrogen:

https://edition.cnn.com/videos/business/2020/03/06/orkney-hy...

You don't need carbon to store energy, you can just stop at hydrogen (or use nitrogen to make ammonia).

Processes can be refitted to use pure hydrogen or it can just be added in small increments to existing gas burning plants.

Replacing anything that burns fuel with carbon in it with alternatives that dont is a better solution.

Lots of homes and buildings use natural gas for heat. It would be nice to replace that with something carbon neutral, but the infrastructure can't handle hydrogen levels above 10-20%.

hydrogen is notoriously difficult to store. Being an atom "thick" generally means it leaks through containers regardless of what you try to do.

And I don't know if you've played the game "Oxygen Not Included", but creating liquid hydrogen is no easy task either.

A more dense energy storage substance (such as a hydrocarbon) would probalby be more efficient in terms of transportation / use / storage.

I didn’t expect to see ONI in a hacker news thread!

Yes, hydrogen is an absolute mess to handle in free form, while hydrocarbons... stable, energy dense, and something we’ve had experience working with for a couple of centuries now.

A nice side effect would be that synthetic hydrocarbons might possibly reduce the dependency on oil for manufacturing plastics, dyes etc. It’s incredibly exciting... I don’t see how this isn’t a huge win.

Hydrogen leaks in an oxygen atmosphere (like the one here on earth) are pretty dangerous, as they are effectively invisible in daylight, due to almost all the energy going directly to infrared. Due to that NASA test engineers used to walk with a broom in front of them in areas where hydrogen leaks could happen. If the broom suddenly caught fire, there was a burning hydrogen leak in front of the engineer! A picture of this can be seen here:

https://spinoff.nasa.gov/spinoff1997/ps1.html

Not just leaks, hydrogen can destroy the structure of many metals and make them brittle: https://en.wikipedia.org/wiki/Hydrogen_embrittlement

And another issue is the very low density - you van see it with hydrolox rockets, how big they are & how their liquid hydrogen tanks are compared to the LOX tanks. This adds up in tank weight, removing some of the energy/density benefits. This is one of the reasons many next gen rockets are opting for liquid methane instead of liquid hydrogen.

I was going to ask if anyone knew what the efficiency of this process was. Obviously we can't get a perpetual motion machine out of it, so it must be taking more energy to form the syngas than gets released from the fuel in the first place, right?

Right.

Reply on news.ycombinator.com