4 ms·

If water access is the bottleneck, you can build storage and reuse it. 1 GWh of hydrogen is equal to 30 tons, or 270 tons of water. That's so small you can lite

If water access is the bottleneck, you can build storage and reuse it. 1 GWh of hydrogen is equal to 30 tons, or 270 tons of water. That's so small you can literally order a prefab off the internet here in Australia, installed and delivered for $10k. Extrapolated, that would represent $0.01/kWh in capital costs, or a complete rounding error of costs over the lifetime of the plant. You could even truck it in from a thousand miles away without really impacting the cost very much. To explore the problem a different way, here in Australia, 8 million megaliters of water was used in farming in the last year. Total energy consumption (not just electricity) in the same period was 1714 TWh. Storing 3 weeks of our energy needs would require 26,700 megaliters of water be converted to hydrogen, or 0.3% of the amount yearly used in farming, already distributed in regional areas.

Manfredo_1 6y ago
The challenge lies in moving the water, not in building a container to store it. > You could even truck it in from a thousand miles away without really impacting the cost very much. Lets' do the math. Trucking costs ~$.15 per short ton per mile as per Google. So shipping 270 tons over 1,000 miles works out to $40,000. And you're using the thermal energy density of hydrogen, not the electrical energy density - as in, accounting for inefficiency of electricity generation. 1 GWh thermal is typically 500 MWh electrical for both fuel cells and turbines. The actual cost would be double that, given that most systems are 40-60% efficient. So if by "without really impacting the cost vey much" you mean "increasing the cost by a factor of 5-9x", then sure. Moving large amounts of water is energy intensive, most infrastructure built to move water relies on gravity to move water from alpine reservoirs to lowlands. And unless you're capturing the output of whatever you're using to transform hydrogen back into electricity, then this is a recurring cost not a capital cost. This is easier to do for some implementations, like electrochemical cells, but much harder for gas turbines.
- reitzensteinm 6y ago
  Yeah, I mean in the case where you're recapturing the water. Trucking it to use it once is madness, and storage isn't really relevant if you've got a pipeline or a river to draw from. You're totally right about thermal vs electrical, even with a fuel cell.
  - pfdietz 6y ago
    If the volume involved is high enough to be problematic, it's high enough to justify building pipelines. The cost of trucking is irrelevant.
    - reitzensteinm 6y ago
      Right. I was just sketching out that you could build it self contained in a desert if you really had to and still make it economical. Ad absurdum only, not a serious suggestion.
pfdietz 6y ago
0.3% of water used for irrigation would be totally fine. The heat of formation of water is 13 MJ/kg. If we can convert hydrogen to power at 50% HHV efficiency, this means 1000 TWh of storage would require hydrogen from about 1/4 of a cubic kilometer of water. This is small compared to the water used in the US for irrigation (about 100 cubic kilometers per year). (It would be somewhat higher than this due to the need to reject waste heat from the bottoming cycle of the CC plant, and at the electrolysers and hydrogen compressors.) A key point, though, is that nuclear uses water too, for cooling. For every MJ of power from a reactor, 2 MJ of waste heat is produced, and this heat goes out the cooling towers (there are dry cooling solutions, but they make nuclear even more expensive, less efficient, and less competitive). The heat of evaporation of water is 2.26 MJ/m^3, so 1000 TWh of power from nuclear would require evaporating 1.6 cubic kilometers of cooling water. But it's worse than that. Hydrogen only has to handle the last slice of power demand (that 500 TWh is about 1/9th the US annual power consumption; your 3 weeks out of 52 would be even less), but nuclear would have to produce all of it, or at least a major chunk (and the reactors have to operate at high capacity factor or the cost of their power becomes even more ludicrous). So the water use of nuclear would actually be an order of magnitude higher than that. The water argument is an argument for wind and solar (and hydrogen), not an argument for nuclear.

Manfredo_1 6y ago

The challenge lies in moving the water, not in building a container to store it. > You could even truck it in from a thousand miles away without really impacting the cost very much. Lets' do the math. Trucking costs ~$.15 per short ton per mile as per Google. So shipping 270 tons over 1,000 miles works out to $40,000. And you're using the thermal energy density of hydrogen, not the electrical energy density - as in, accounting for inefficiency of electricity generation. 1 GWh thermal is typically 500 MWh electrical for both fuel cells and turbines. The actual cost would be double that, given that most systems are 40-60% efficient. So if by "without really impacting the cost vey much" you mean "increasing the cost by a factor of 5-9x", then sure. Moving large amounts of water is energy intensive, most infrastructure built to move water relies on gravity to move water from alpine reservoirs to lowlands. And unless you're capturing the output of whatever you're using to transform hydrogen back into electricity, then this is a recurring cost not a capital cost. This is easier to do for some implementations, like electrochemical cells, but much harder for gas turbines.

reitzensteinm 6y ago
Yeah, I mean in the case where you're recapturing the water. Trucking it to use it once is madness, and storage isn't really relevant if you've got a pipeline or a river to draw from. You're totally right about thermal vs electrical, even with a fuel cell.
- pfdietz 6y ago
  If the volume involved is high enough to be problematic, it's high enough to justify building pipelines. The cost of trucking is irrelevant.
  - reitzensteinm 6y ago
    Right. I was just sketching out that you could build it self contained in a desert if you really had to and still make it economical. Ad absurdum only, not a serious suggestion.

pfdietz 6y ago

0.3% of water used for irrigation would be totally fine. The heat of formation of water is 13 MJ/kg. If we can convert hydrogen to power at 50% HHV efficiency, this means 1000 TWh of storage would require hydrogen from about 1/4 of a cubic kilometer of water. This is small compared to the water used in the US for irrigation (about 100 cubic kilometers per year). (It would be somewhat higher than this due to the need to reject waste heat from the bottoming cycle of the CC plant, and at the electrolysers and hydrogen compressors.) A key point, though, is that nuclear uses water too, for cooling. For every MJ of power from a reactor, 2 MJ of waste heat is produced, and this heat goes out the cooling towers (there are dry cooling solutions, but they make nuclear even more expensive, less efficient, and less competitive). The heat of evaporation of water is 2.26 MJ/m^3, so 1000 TWh of power from nuclear would require evaporating 1.6 cubic kilometers of cooling water. But it's worse than that. Hydrogen only has to handle the last slice of power demand (that 500 TWh is about 1/9th the US annual power consumption; your 3 weeks out of 52 would be even less), but nuclear would have to produce all of it, or at least a major chunk (and the reactors have to operate at high capacity factor or the cost of their power becomes even more ludicrous). So the water use of nuclear would actually be an order of magnitude higher than that. The water argument is an argument for wind and solar (and hydrogen), not an argument for nuclear.