4 ms·

I'm wondering why we don't use hydrolysis -> store hydrogen -> burn hydrogen -> run a steam turbine for energy storage. Efficiency would be low, at about 70% *

by ajuc 6y ago

I'm wondering why we don't use hydrolysis -> store hydrogen -> burn hydrogen -> run a steam turbine for energy storage. Efficiency would be low, at about 70% * 60% ~= 40% but capacity would be huge. 1 kg of hydrogen has specific energy of over 140 MW. We could even capture CO2 as well with that energy and make methan and use normal gas powerplants for retrieving the power :) Just build double the number of solar panels to account for efficiency loses. Should be cheaper than grid-scale energy storage with 90%+ efficiency.

_ph_ 6y ago
Hydrogen is difficult and consequently expensive to store. Also, the low efficiency is a problem. Pumped storage hydroelectricity is way more efficient.
- ajuc 6y ago
  Then combine with carbon from air and store methane. Pumped is great when you have the geography for it but most countries don't. And building dams is pretty harsh on the environment too, just in different ways than CO2 emmisions.
  - _ph_ 6y ago
    Right, I think we will convert any hydrogen produced via electrolysis to methane for better storage. That methane would be completely compatible with the storage/distribution/usage infrastructure which many countries already have in place. I was commenting on the statement, that hydrogen by itself is easily stored.
- rklaehn 6y ago
  At small scale, this is correct. At very large scale, hydrogen is incredibly easy to store. You can just fill up and old depleted gas well and store terawatt-hours of energy easily. Germany has enough gas well storage to survive several months. This infrastructure is currently used for natural gas, but it can be repurposed for hydrogen. I still think that commoditized battery storage will win in the end, but storage cost is not an argument against hydrogen.
  - _ph_ 6y ago
    Besides it is not trivial to repurpose natural gas storage for hydrogen - you need an entirely different level of tightness, you would be disappointed about the amount of energy you can store this way, as hydrogen is way less dense than natural gas, so the capacity of the storage would be poor.
    - rklaehn 6y ago
      For very large scale storage we are not talking about steel pressure vessels that are subject to hydrogen embrittlement, but depleted natural gas reservoirs which are just gas-tight geological formations and have no issues whatsoever with hydrogen embrittlement. For small and medium scale storage you are right. Which is why hydrogen for cars and even trucks is a bad idea.
      - _ph_ 6y ago
        And you would get much less hydrogen stored at the same pressure than methane. To store reasonable amounts of hydrogen, you need very high pressures. Gas powered cars use like 60 bars of pressure, hydrogen 700.
        rklaehn 6y ago
        Yes, that is correct. But the end to end efficiency of Electricity -> H2 -> Electricity is much better than Electricity -> H2 -> CH4 -> Electricity. Hydrogen at 0°C and 100 Bar (~10MPa) has a density of 8.3447 kg/m^3. It has an energy density of 120 MJ/kg. So about 33 kWh/kg. So you end up with 278 kWh/m^3. Now of course you have to multiply this by the H2->Electricity efficiency. Let's be very pessimistic and take 0.6 or 60%, which is what a gas turbine plant can achieve today. You end up with 166 kWh/m^3 of usable electricity per cubic meter. One of many german gas storage facilities https://www.nafta-speicher.de/en/company https://www.nafta-speicher.de/en/company has a volume of 1.8e9 m^3. That translates into 300 Terawatt-Hours of storage capacity for just this one facility.
        6y ago
webreac 6y ago
hydrogen as storage is not efficient. This problem is reduced if hydrogen is used for transport.
reincarnate0x14 6y ago
That was part of the old nuclear age dream back when a fleet of reactors would make power too cheap to meter, although using methane or propane instead may be easier to work with from an engineering perspective. Moving energy around as liquefied gas is also significantly more efficient in most circumstances. IIRC there was some study on doing something like that in Germany in the 2000s but I'm not finding references to it now. If you don't have to build the dam (since it already exists), pumping water back up into the reservoir is going to be better in the limited locations you can do that, and given the relatively tiny amount of energy storage vs power production I suspect the economies of scale on that won't change without a preceding sea change in global commitment to fossil fuel retirement. There is also a better transition path to that as we already are building amazingly good gas turbines that could just as well be burning synthesized or biogas on demand from solar or nuclear over-generation. I sort of suspect that may end up being politically poisonous to the people that would normally be pushing for carbon-neutral storage options. It would be way more than double the solar panels though. Solar generation is generally maxing at around 25% capacity factor, so replacing an existing fossil fuel generator requires 4x or more the nominal capacity in solar plus whatever efficiency loss in storage, so going with a pure solar + storage replacement of a 1500 MW combustion plant could easily require 12,0000 MW of equivalent generation.
- ajuc 6y ago
  > It would be way more than double the solar panels though. We're comparing energy storage so no matter how much fossil fuel powerplants we replace - it would be x solar panels for energy storage with 80-90% efficiency (for example this gravicity stuff or hydro or batteries) and 2x for methane synthesis.
kolinko 6y ago
There is a lot of push into hydrogen because of that. I know Germany is doing that.
imtringued 6y ago
Germany is already investing into power to gas infrastructure for both hydrogen and methane. What you are talking about is already reality albeit at a small scale.

by ajuc 6y ago

_ph_ 6y ago

Hydrogen is difficult and consequently expensive to store. Also, the low efficiency is a problem. Pumped storage hydroelectricity is way more efficient.

ajuc 6y ago
Then combine with carbon from air and store methane. Pumped is great when you have the geography for it but most countries don't. And building dams is pretty harsh on the environment too, just in different ways than CO2 emmisions.
- _ph_ 6y ago
  Right, I think we will convert any hydrogen produced via electrolysis to methane for better storage. That methane would be completely compatible with the storage/distribution/usage infrastructure which many countries already have in place. I was commenting on the statement, that hydrogen by itself is easily stored.
rklaehn 6y ago
At small scale, this is correct. At very large scale, hydrogen is incredibly easy to store. You can just fill up and old depleted gas well and store terawatt-hours of energy easily. Germany has enough gas well storage to survive several months. This infrastructure is currently used for natural gas, but it can be repurposed for hydrogen. I still think that commoditized battery storage will win in the end, but storage cost is not an argument against hydrogen.
- _ph_ 6y ago
  Besides it is not trivial to repurpose natural gas storage for hydrogen - you need an entirely different level of tightness, you would be disappointed about the amount of energy you can store this way, as hydrogen is way less dense than natural gas, so the capacity of the storage would be poor.
  - rklaehn 6y ago
    For very large scale storage we are not talking about steel pressure vessels that are subject to hydrogen embrittlement, but depleted natural gas reservoirs which are just gas-tight geological formations and have no issues whatsoever with hydrogen embrittlement. For small and medium scale storage you are right. Which is why hydrogen for cars and even trucks is a bad idea.
    - _ph_ 6y ago
      And you would get much less hydrogen stored at the same pressure than methane. To store reasonable amounts of hydrogen, you need very high pressures. Gas powered cars use like 60 bars of pressure, hydrogen 700.
      - rklaehn 6y ago
        Yes, that is correct. But the end to end efficiency of Electricity -> H2 -> Electricity is much better than Electricity -> H2 -> CH4 -> Electricity. Hydrogen at 0°C and 100 Bar (~10MPa) has a density of 8.3447 kg/m^3. It has an energy density of 120 MJ/kg. So about 33 kWh/kg. So you end up with 278 kWh/m^3. Now of course you have to multiply this by the H2->Electricity efficiency. Let's be very pessimistic and take 0.6 or 60%, which is what a gas turbine plant can achieve today. You end up with 166 kWh/m^3 of usable electricity per cubic meter. One of many german gas storage facilities https://www.nafta-speicher.de/en/company https://www.nafta-speicher.de/en/company has a volume of 1.8e9 m^3. That translates into 300 Terawatt-Hours of storage capacity for just this one facility.
        6y ago

webreac 6y ago

hydrogen as storage is not efficient. This problem is reduced if hydrogen is used for transport.

reincarnate0x14 6y ago

That was part of the old nuclear age dream back when a fleet of reactors would make power too cheap to meter, although using methane or propane instead may be easier to work with from an engineering perspective. Moving energy around as liquefied gas is also significantly more efficient in most circumstances. IIRC there was some study on doing something like that in Germany in the 2000s but I'm not finding references to it now. If you don't have to build the dam (since it already exists), pumping water back up into the reservoir is going to be better in the limited locations you can do that, and given the relatively tiny amount of energy storage vs power production I suspect the economies of scale on that won't change without a preceding sea change in global commitment to fossil fuel retirement. There is also a better transition path to that as we already are building amazingly good gas turbines that could just as well be burning synthesized or biogas on demand from solar or nuclear over-generation. I sort of suspect that may end up being politically poisonous to the people that would normally be pushing for carbon-neutral storage options. It would be way more than double the solar panels though. Solar generation is generally maxing at around 25% capacity factor, so replacing an existing fossil fuel generator requires 4x or more the nominal capacity in solar plus whatever efficiency loss in storage, so going with a pure solar + storage replacement of a 1500 MW combustion plant could easily require 12,0000 MW of equivalent generation.

ajuc 6y ago
> It would be way more than double the solar panels though. We're comparing energy storage so no matter how much fossil fuel powerplants we replace - it would be x solar panels for energy storage with 80-90% efficiency (for example this gravicity stuff or hydro or batteries) and 2x for methane synthesis.

kolinko 6y ago

There is a lot of push into hydrogen because of that. I know Germany is doing that.

imtringued 6y ago

Germany is already investing into power to gas infrastructure for both hydrogen and methane. What you are talking about is already reality albeit at a small scale.