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Comment by rob74 | Hacker News Reader

I'm definitely no expert here, but...

"Storing" electricity using H2 is relatively straightforward: use electricity to electrolize water and get H2 (and O2), store the H2 (presumably liquefied) and then burn it to either generate electricity again or to power existing energy-intensive processes (e.g. smelting iron ore). Not sure how efficient the electricity -> H2 -> electricity conversion is, but ok...

Now, if you use methanol, you get the H2 like before, then "make it react" with CO2 (and CO2 is not really eager to react with anything IIRC) to get methanol, and then you burn it, getting CO2 which has to react with more H2 or otherwise you wouldn't be carbon neutral. Sounds to me like this process can only be less efficient (and more complicated) than the H2 process? Potentially much less efficient and much more complicated?

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The key argument of the paper this is based on is that storing H2 is difficult if you don't have salt caverns. Then you need H2 pressure tanks, and that is expensive and also requires a lot of energy. And you don't have salt caverns everywhere.

The authors compare this in an energy model, and come to the conclusion that methanol comes out on top if you don't have cheap (aka salt cavern) h2 storage. But of course, there are a lot of assumptions going into this.

Nice bonus: It's an open source model, so others can test it with different assumptions.

H2 storage can also be done by liquefaction, which is a lot more practical than compressed when we are talking longish-term storage. Yes, you will use energy to cool and liquefy H2, but a lot of this can be recovered when you go back again.

Even the H2 process is horribly inefficient. Just use the electricity directly and store the small amount that is needed for peak levelling in ordinary batteries.

All these ways of using hydrocarbons are less efficient than batteries and only make sense when the hydrocarbon has a higher energy density and when the density is actually needed.

Just install a battery in every new home, make all new homes comply with passivhus standards, put solar panels on top of all new commercial buildings, generally stop wasting energy. And strengthen the interconnects between countries so that places like Spain can sell excess solar to France and thence on to the rest of Europe.

There is a difference between short-term and long-term storage. Smoothing out hourly or daily variations is pretty easy with batteries or hydro. The problem is deficits on cloudy, calm winter days. The amount of batteries would to cover a week would be too expensive.

For now, this would be covered by gas plants but at some point need to have green solution. It is also possible to over build solar and wind to cover more days and produce excess capacity. Generated fuels work well for long-term storage since can be generated when there is excess, stored for long period of time, and are used by long-distance vehicles.

> There is a difference between short-term and long-term storage.

True. But there's no reason you can't use both.

So the "smooth out daily variation" and "store energy to address seasonal changes" are 2 problems that can be attacked independently. Maybe some solution(s) may be useful for both jobs, but this is not necessary.

I suspect in most cases, batteries will be more practical / economical for short-term storage. For long-term storage (or transporting energy across the globe) methanol is just one of many options.

> Just install a battery in every new home, make all new homes comply with passivhus standards, put solar panels on top of all new commercial buildings, generally stop wasting energy.

We should definitely do all that. But even that isn't going to be enough. What do you do about the gazillions of existing homes that can't be well insulated, don't have space for solar panels or heat pumps etc.

I have a quite modern house (built in the 50s) but I can't get a heat pump because it has microbore heating.

> I have a quite modern house (built in the 50s) but I can't get a heat pump because it has microbore heating.

Get an air-to-air heat pump like we use in Scandinavia. A quarter the price and a better coefficient of performance. Doesn't heat your water of course.

I'll add that German plans up to now were to build turbines that could take both gas and H2. Even though these have very different combustions. H2 was brought in to power the green transition. The turbines were to be developed.

Now they're actually planning them and cutting cost, surprise surprise, the turbines are gas only.

> I'm definitely no expert here, but... "Storing" electricity using H2 is relatively straightforward

Never assume that anything is easy at scale.

I remember watching my high school chemistry teacher generate hydrogen and oxygen, and then burn the hydrogen. (And show that a match became more intense in pure oxygen.)

But that doesn't mean it's "relatively straightforward" to do that on massive scale: It turns out the electrodes were a precious metal, and the water had to be fresh water. If you run electrolysis in seawater, you get chlorine gas instead of pure oxygen.

Also, don't forget that it's very hard to compress hydrogen. Without going into the details: Compressing hydrogen takes energy, and keeping it cold (so it stays compressed) also takes energy. (It's hard to compress hydrogen to have the same energy density as propane.) And then, getting electricity back from hydrogen isn't 100% efficient.

If you're not careful, the cost to make hydrogen, store it, and then generate electricity back can be more than what the electricity is worth.

(FYI: Estimates for hydrogen cars put the electricity -> hydrogen -> electricity path at roughly 50% efficiency, compared to electricity -> battery -> electricity, which is > 90%. This generally implies that hydrogen will cost more, per mile, than electricity.)

Where synthetic liquids (and indeed methane) can be interesting is if you want to ship the energy somewhere. So you can make the methanol somewhere with abundant cheap electricity and CO2, then ship or pipe it to places which lack that.

It's a lot easier and cheaper to transport methanol or methane (either piped or in the form of LNG) than H2 since it takes a lot leas space and we already have a lot of infrastructure for it.

In the long run it is cheaper to transport the energy as electricity.

That depends on the distances involved - eg if you want to generate cheap solar electricity in the Middle East or South America and export it to Europe or North America (which is something people in the industry have discussed as being potentially economical in the long term) this isn't really practical.

My amateur understanding is that the benefits are: A) H2 is exceptionally difficult to store at scale. Salt caverns are an option, but that is limited B) methanol can be used off the shelf by existing generators so the prices are much more economical and they can use both fuels during a transitory period

Liquid H2 requires cryogenic tanks. The tank will loose heat, so need continuous power to keep it cool. Or there will be H2 leak over time that will empty the tank. When BMW made their hydrogen combustion engine, the tank would get empty within a month of parking turned off.

The continuous power though is actually quite minuscule in this context. NASA has a lot of test data published, e.g. for their 125 000 liter storage tank, the heat ingress in 24 h is 7.2 kWh while the energy content of the hydrogen in the tank is 290 000 kWh.

What is being proposed for energy storage is signficiantly larger than this, and then the square-cube-law gives even less heat ingress as compared to the energy of the tank contents.

The question is still what’s more efficient and cheaper. If storing a huge amount of liquid hydrogen in a tank and using a % of it to keep it liquid is cheaper than the methanol infrastructure and its multiple conversions, then it will succeed.

Only if you leave out the part about storing H2 in a tank vs storing methanol in a tank. There is a reason why they say without salt caverns to store H2, this is the cheaper process.

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