[5ersi]

So this process is "CO2 hydrogenation" meaning that it needs elemental hydrogen, which is not naturally available (except in trace amounts). To make this work one needs to first produce hydrogen which is itself an energy consuming process.

So basically, we'd burn fossil fuels producing CO2 and then reverse this process via "CO2 hydrogenation" (with significant losses) to again get the hydrocarbons (aka gasoline) ?

This whole thing would only make sense if we had abundant source of elemental hydrogen. But then why burn fuel in the first place.

(This would only make sense if all fuel totally ran out and then we'd need this process to make hydrocarbons for material use: plastics, etc..)

[chii]

> This whole thing would only make sense if we had abundant source of elemental hydrogen. But then why burn fuel in the first place.

water is an easy elemental source of hydrogen. If it is possible to fuel this electrolysis via cheaply obtained renewable energy, then it makes a lot of sense to produce fossil fuels using this method - it will allow the existing infrastructure to consume such produced fuels, so you save capital and energy on replacing them.

[danuker]

Absolutely. Look at intraday electricity prices, and you see that the energy is cheapest when the sun is shining.

Problem is, if you use it for cooling, it's strictly better to use the electricity directly (chances are the sun is shining when it's hot).

And if you use it for heating (at least from day to night), the round-trip efficiency is probably still better for batteries, or electric heating + hot water storage, because you can use heat pumps which are say, 5x more efficient than burning fuel.

[marcosdumay]

Eh... There are more uses for fuel than cooling and heating.

If you have an stationary application you will never use something like that. (Except maybe for long time storage, I don't think this will win over long time storage, but it isn't settled.)

[5ersi]

> water is an easy elemental source of hydrogen.

Sorry but this goes against the definition in elemental form (in this case it's H2).

Also there is no such thing as `cheaply obtained renewable energy`. If it was your electricity bill would be 0.

[kingkawn]

Why not use that electricity to power electric motors instead tho

[fsh]

This requires batteries which are very heavy. This is not a big problem in cars, but an absolute deal breaker in aircraft. The energy consumption of a plane scales roughly with the weight, which makes efficient battery powered flight pretty much impossible.

[pengaru]

The mass problem in larger aircraft is mostly just an issue with landing AIUI.

One could imagine battery boosters jettisoned after supporting the climb to cruising altitude which autonomously return as drones to the airport.

[dahfizz]

Current battery tech just isn't that good. A Tesla battery pack weighs 900 pounds and only holds the energy of 3 gallons of gas. They are also a hell of a lot more expensive and wear faster than a gas tank.

Carbon hydrogen bonds are one of the best ways to store energy that we have.

[anamax]

> A Tesla battery pack weighs 900 pounds and only holds the energy of 3 gallons of gas.

A Tesla battery pack is good for about 300 miles. If that's equivalent to 3 gallons of gas, that's saying that Teslas would get 100mpg.

I can believe 40-45 mpg, but 100 requires some evidence.

[dahfizz]

https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=43401

They are rated for 134 combined MPGe. That is not that crazy for an EV, the ford Mach E gets 93:

https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=43602

Electric drivetrains are really efficient, which is why EV's are practical at all.

[bregma]

What if you had massive amounts of virtually free energy just falling out of the sky in one or a few isolated locations, but only for a few hours every day, and your consumption patterns required an available-24-by-7 safely transportable consumer-safety-level supply?

Carbon-hydrogen bonds are an relatively efficient and safe way of storing energy and we have well-developed technology and infrastructure in place to take advantage of that.

[H8crilA]

https://en.m.wikipedia.org/wiki/World_energy_supply_and_cons...

It is hilarious how many people think the problem is with reversing the CO2 creation. No, it's a matter of getting the joules to sustain the modern lifestyle and the population count.

[CPLX]

Primary energy assessment follows certain rules[note 1] to ease measurement of different kinds of energy. These rules are controversial. Water and air flow energy that drives hydro and wind turbines, and sunlight that powers solar panels, are not taken as PE, which is set at the electric energy produced. But fossil and nuclear energy are set at the reaction heat which is about 3 times the electric energy. This measurement difference can lead to underestimating the economic contribution of renewable energy.[7]

Seems relevant

[iso1210]

That says global 'consumption' is about 80000 TWh a year. Incoming solar energy is about 1700 times that

[anamax]

> That says global 'consumption' is about 80000 TWh a year. Incoming solar energy is about 1700 times that

Assuming that you still want oceans to work, about 2/3rds of that is not available, which get us to 500x. You also want land-based plants to work, which gets us to <250x and much of the remainder is unsuitable, so let's call it <100x.

"make equipment" through end-use solar is <20%, so we're down to <20x.

What else am I missing?

[alduin32]

Wouldn't absorbing 0.06% of the incoming solar energy have a significant impact on the planet's ecosystems, either by the absorbed energy by the massive production of PV and storage required for that end ?

I think that your statement does not rebutt the parent comment : producing the energy required to sustain our modern lifestyle and population count will have significant impacts on the ecosystems, whatever the source we use for that energy.

[fsh]

All generated primary energy will eventually be turned into heat. However, the climate effect of this direct heating is orders of magnitude smaller than the greenhouse effect from burning hydrocarbons.

[H8crilA]

Minimal effect compared to the greenhouse effect of +2, +3 or even +4C. Like not even close.

[H8crilA]

Indeed, there is hope! And note how fast the renewables portion is growing, we're looking at a fairly good projection here: 1, 2, maybe 3 decades ahead of us it should get really substantial. The biggest problem is the EROEI, which is a lot higher for the clean stuff, though still improving.

[IMTDb]

Wait, does the mean that if we wanted to use solar as an energy source for the world we would need to cover roughly 1/1700 of the entire surface of the planet with perfectly efficient panels and interconnections between the east and the west to support the energy transfer during nighttime ?

[teamonkey]

Back of the envelope calculations.

1) Assume a 1x1m solar panel generates 150W at peak.

2) It won't manage that all the time, far from it. Lets say it generates 300Wh per sq. meter. per day, or 110kWh/m^2/year.

To achieve 80000TWh we'd need about 730million 1x1m panels. For comparison, google says the land area of New York city is 783million m2.

[fsh]

You are off by a factor 1000. 80 PWh is 730 billion times 110 kWh.

[teamonkey]

Sorry, you're right. You'd need to cover a land area slightly larger than Texas.

[masta]

Not to mention that it requires capturing and probably liquifying the CO2 first, which is also energy intense. If we do CO2 Hydrogenation, it will be for Methane gases, not liquid. Methane is easy to store, has rather flexible uses and would help in keeping the grid stable.

Liquids, especially when used in ICE engines later on, would result in an energy efficiency of 5-10% max. This is abysmal and we could use that otherwise wasted energy to decarbonize many other things by directly electrifying them.

[ben_w]

Can also make sense if this is cheaper than batteries.

Electrolytic hydrogen is so easy I did it when I was nine years old — the only reason I powered the reaction using a battery instead of PV was that back in 1992, PV wasn't something a kid could easily get hold of with pocket money.

[gefhfffh]

Well, short term it may be cheaper. Long term you are going to pay, because the efficiency is horrible, 10-30% depending on who u ask

[ben_w]

PV is so cheap the efficiency is the least important part of this.

PV without batteries is the cheapest power source on earth, bids in the order of single US ¢ / kWh, but last I saw batteries had LCOE comparable with nuclear reactors (about 15¢/kWh in 2020).

I’m certainly hopeful that batteries will improve, but right now even a mere 10% efficient process for turning electricity into gasoline and then burning it is still useful as both heating and aviation fuel, and just about on the edge of useful as strategic diversity for nations that don’t want to limit strategic energy storage to just batteries.

[gefhfffh]

PV needs physical resources that aren't for free or unlimited. PV needs space. Most energy used has still an high negative impact on the atmosphere. Low efficiency somewhere is energy potentially wasted that could reduce carbon emissions somewhere else.

Heating is waaay more efficient with heat pumps. Aviation... Well who can still afford it...

There are other forms of storage as well, e.g. hydro, heat storage, and many more

I'm not saying it doesn't have it's uses, but efficiency is important

[ben_w]

> PV needs physical resources that aren't for free or unlimited. PV needs space.

We have about 10,000 times as much space as we need for a pure-solar economy at current power use, 1,000 times what we need if we raise everyone to the power use of the average American, but still better than 100 times what we need if we want to do that while having a 10% efficient storage system because most energy is used while the sun is up anyway.

> Most energy used has still an high negative impact on the atmosphere.

Yup, and will do until it’s renewable. If it was already renewable, using that power to make more renewables has no impact whatsoever.

> Low efficiency somewhere is energy potentially wasted that could reduce carbon emissions somewhere else.

Sure, but the ideal is a global superconducting grid, and even if you do that the easy way [0] we’re a long way from the necessary industrial base to get it done.

This option is sufficiently good to be interesting in the meantime.

[0] a ballistic superconductor, specifically a charged non-conductive ring in orbit.

Second best option: a few square meter cross section HVDC cable encircling the planet, which needs quite a big investment in mining to get the materials for but has the advantage we can get most of it done gradually just by continuously upgrading existing grids until the very last step of crossing the Atlantic and/or Pacific.

[danuker]

> Heating is waaay more efficient with heat pumps.

Absolutely.

With electricity you can power heat pumps (which are say, 5x more efficient than resistive heaters), but by synthesizing fuels with electricity, you can get strictly less than a resistive heater's equivalent energy.

[Ourgon]

> Aviation... Well who can still afford it...

Oddly enough (but not really that odd) it seems to be affordable to a lot of people who jet around the globe to tell each-other and the media that people need to fly less, for the climate. It used to be for the environment but that trope seems to be worn out.

[marcosdumay]

> because the efficiency is horrible, 10-30% depending on who u ask

You mean the electrolysis efficiency? There are examples of up to 70% on the lab, but it was never economically important to optimize it.

[Gravityloss]

Hydrocarbon fuels are a lot more energy dense than batteries or hydrogen (with tankage), so they are needed for things like long distance flight for now.

[dahfizz]

They also make for great storage. Using solar to make a hydrocarbon fuel which is turned into electricity in our existing fossil fuel infrastructure seems way more plausible than spending trillions on batteries or pumped hydro.

[enrgtw2022]

Yep.

Batteries aren't great for super-cold areas. Pure hydrogen, my understanding is that it's pretty much impossible to make a 'leak free' tank. So for things like backup power generation there is an additional challenge. More thinking about need to top off than risks, I'm not qualified to speak to whether such a tank would be a risk.

[fsh]

I don't think that leakage is a serious issue in high-pressure hydrogen storage. The tanks used in hydrogen fuel cell vehicles have leakage rates of a few mL/minute [1]. The first generation Toyota Mirai has a storage capacity of 85000 standard liters of hydrogen. It would take tens of years to leak out a significant fraction of that.

[1] https://link.springer.com/article/10.1007/s42154-020-00096-z

[Gravityloss]

Right battery chemistries with right thermal management and especially right software would work well also in cold climates. Bjørn Nyland from Norway tests a lot of this stuff on youtube.

[bryanlarsen]

Why do this? Because we don't have electric or hydrogen airplanes yet, and it takes forever to approve an airplane and for it to become widespread.

Even if it is only 10% efficient, some form of carbon capture is going to be required to hit carbon zero. This is one of the most promising mechanisms for carbon capture.

[jiri]

stored hydrocarbons are way more easy to handle than stored h2. On top of that, h2 is hard to contain, it can leak everywhere.

[pfdietz]

The energy has to come from somewhere.

[mlatu]

yes, and it is our duty to think about where we lose it and how not to.