4 ms·

I wonder if something using hydrogen as the buffer would work - it has a density of 37 kWh/kg (or 2.4 kWh/litre). Instead of fuel cells (which are still expens

I wonder if something using hydrogen as the buffer would work - it has a density of 37 kWh/kg (or 2.4 kWh/litre). Instead of fuel cells (which are still expensive and relatively low capacity), using excess electricity to electrolyse water. The oxygen and hydrogen can be stored in tanks, and when you need the power it can be combusted, generate steam and drive turbines. There isn't really any new technology here, so it should be relatively cheap and quick to setup too. What am I missing?

philipkglass 10y ago
The volumetric energy density of hydrogen is very low, so either you need enormous tanks or very strong tanks plus extreme compression. One way of making enormous "tanks" that can tolerate fairly high pressures is by solution-mining caverns out of natural underground salt formations. But this is geographically limited to where such salt formations occur, like parts of Texas and Louisiana. The other problem is that the round-trip energy efficiency isn't great. You might expect 75% efficiency for electricity-to-hydrogen from electrolysis and then 60% hydrogen-to-electricity if you burn it in an efficient combined cycle gas turbine for 45% efficiency overall. Oh, and you irreversibly lose energy as heat when you compress the hydrogen, for further losses. And it's pretty expensive to buy big industrial-scale electrolysis units but run them only during the few hours each day when there's excess renewable energy you want to store (though it becomes a more attractive idea as the penetration rate of renewables, and corresponding excess generation times, increase.)
- imtringued 10y ago
  The conversion factor is not that important because without storage the excess energy would be lost anyway if we assume electricity demand doesn't shift from night to day.

4 ms·

I wonder if something using hydrogen as the buffer would work - it has a density of 37 kWh/kg (or 2.4 kWh/litre). Instead of fuel cells (which are still expens

by lucaspiller 10y ago

philipkglass 10y ago
The volumetric energy density of hydrogen is very low, so either you need enormous tanks or very strong tanks plus extreme compression. One way of making enormous "tanks" that can tolerate fairly high pressures is by solution-mining caverns out of natural underground salt formations. But this is geographically limited to where such salt formations occur, like parts of Texas and Louisiana. The other problem is that the round-trip energy efficiency isn't great. You might expect 75% efficiency for electricity-to-hydrogen from electrolysis and then 60% hydrogen-to-electricity if you burn it in an efficient combined cycle gas turbine for 45% efficiency overall. Oh, and you irreversibly lose energy as heat when you compress the hydrogen, for further losses. And it's pretty expensive to buy big industrial-scale electrolysis units but run them only during the few hours each day when there's excess renewable energy you want to store (though it becomes a more attractive idea as the penetration rate of renewables, and corresponding excess generation times, increase.)
- imtringued 10y ago
  The conversion factor is not that important because without storage the excess energy would be lost anyway if we assume electricity demand doesn't shift from night to day.