3

We generate "green hydrogen" using electrolysis of water which is powered by Renewable energy sources like Solar Panels, Wind mills, Hydro power etc.

When we obtain such hydrogen and store it for use later on to generate electricity, the output can be below 30% of the input electricity.

Why even produce such green hydrogen through sheer wastage of electricity produced through renewable means? Why not directly use that electricity to power industries and homes?

People say "hydrogen can be an alternate fuel". I think we can directly make a transition to "electric vehicles" rather than finding "alternate fuels" endlessly until there are no more options left but "electricity"(green, of course)

0
3

It's a matter of energy density. Compared to lithium-ion batteries, compressed hydrogen gas stores about 150 times as much energy per kilogram, or twice as much energy per liter.

If you're using the energy immediately after generating it, then yes, direct power makes sense. But if you're storing it for later, or need to use it to power something that can't be plugged in (such as an airplane), then you want to store it in a compact form. Something like gasoline would be a better choice than hydrogen (better volumetric density and easier to handle), but we don't know how to turn electricity into gasoline. We do know how to turn electricity into hydrogen.

2
  • The storage part is the important thing here.
    – Erik
    Sep 30 at 8:01
  • 1
    I disagree that we don't know how to turn electricity into gasoline. If we have a source of carbon dioxide, we can turn electricity into gasoline. Why it's not done is that (1) the energy efficiency of the whole chain including Fischer-Tropsch reactor is way too low to even remotely make economical sense, (2) we don't have enough stationary sources of sustainable carbon dioxide. So if the carbon dioxide is not sustainable, the produced gasoline won't be sustainable either. Capturing the gaseous carbon dioxide emissions of moving vehicles for reuse makes even less sense than using hydrogen.
    – juhist
    Sep 30 at 16:01
1

Try to use electricity and nitrogen to create ammonia for fertilizer production. I'm sure you see the difficulties in that, as electricity is not an element and thus the only element you have is nitrogen. The element hydrogen is missing. Ammonia requires hydrogen and nitrogen.

Then, try to use electricity to create hydrogen from water (electrolysis) and use that hydrogen and nitrogen to create ammonia for fertilizers. Now you have all the elements you need to make the ammonia molecules.

Similarly, I'm sure that iron production from iron ore is far easier to be done with hydrogen (that takes the oxygen from the iron ore away and makes water as a byproduct) instead of direct electricity. I have heard about plans to make iron using hydrogen to replace coal-based iron production, but have never heard about plans to make iron using direct electricity. However, later on in the steel production chain you might need an electric arc furnace if you need high temperatures, and that actually uses direct electricity and not hydrogen.

Also hydrogen is very easy to store. Salt cavern storage costs about 50 euros per cubic meter. If you can cram hydrogen there at a pressure of 100 bar, it's 0.5 euros per natural cubic meter of hydrogen. A natural cubic meter weighs 0.08988 kg so at density if about 120 MJ/kg (using the lower heating value here) or 33.333 kWh/kg, a natural cubic meter stores approximately 3 kWh. So storage cost is 0.5 EUR / 3 kWh or 0.167 EUR / kWh. The current batteries cost 100 EUR / kWh, nearly three orders of magnitude difference. Even if you take into account that converting hydrogen back to electricity has 50% energy efficiency, hydrogen storage is still 300 times cheaper than lithium ion. Why is this important? Because if you live anywhere far away from the equator, solar power is heavily seasonal. You get lots of it during summer, and practically nothing at winter. Solar power (specifically, photovoltaics, as solar-thermal is very expensive and its cost is not falling exponentially) is projected to become the cheapest electricity production method. Hydrogen allows storing solar power created during summer for consumption during winter. Batteries are way too expensive for seasonal energy storage, although in areas near the equator batteries win for charging during every day and discharging during every night (because batteries have 99% efficiency compared to 75% for hydrogen production and 50% for converting back into electricity or 37.5% for the whole hydrogen chain).

And before you claim that hey let's transport solar power from equatorial deserts long distances, remember that electricity transportation has very large losses and is extremely expensive. Electricity has to be produced near where it's consumed. (Actually you could transport the power as hydrogen using very low losses, having far cheaper transmission pipelines than electricity transmission lines. The trouble is creating that hydrogen in the first place has high losses and converting that hydrogen back into electricity has high losses.)

I agree that whenever electricity is available, it should be consumed immediately. If electricity production all the time matches consumption, then you only use electricity immediately. But production using intermittent renewables never matches the consumption, and that's why you need storage. Batteries win for storage between days, hydrogen wins for storage between seasons.

So what you are missing is failing to realize that renewables are intermittent. If we could produce load-adjustable nuclear power plants cheaply enough then you'd be partially right, hydrogen would not be needed for anything apart from chemical reactions that require hydrogen.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.