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> You could in principle centralize ammonia production with sufficient reactant reserves to ensure continuous production from variable low-density energy source

• jandrewrogers 2y ago
  Energy density mostly and being able to deliver that power where you need it. Aluminum plants are co-located with large-scale power plants, famously hydroelectric, for the same reason. Above certain power requirements, you essentially need the power generation to be onsite. Hydrogen requires 3x the energy of aluminum per ton, so it is an even bigger problem for hydrogen. Unlike aluminum, it is feasible to have large numbers of small hydrogen production plants but then you need to transport all that hydrogen at an acceptable scale.
  • deleted 2y ago
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  • lurk2 2y ago
    > Above certain power requirements, you essentially need the power generation to be onsite. Is this due to transmission losses or just because you couldn't feasibly build enough capacity cables to transmit large amounts of power over long distances?
    • jandrewrogers 2y ago
      A single ton of hydrogen requires ~50 MWh of electricity. Small special-purpose ammonia plants, which are common for some industrial applications, typically require on the order of 50 tons of hydrogen per day. This would require ~2.5 GWh of electricity per day via electrolysis. To put that in context, that is in the same ballpark as the average output of the largest solar farms ever built in the US. The largest ammonia plant in the US requires around 2,000 tons of hydrogen per day. That would require 100 GWh per day to produce by electrolysis, which would require the entire output of a large hydroelectric or nuclear power plant, much like large aluminum refineries. Otherwise, you need to move a lot of electricity or a lot of hydrogen to have good efficiency, and there is infrastructure for neither. Converting natural gas into hydrogen is also energy intensive. One of the big advantages of natural gas is that your hydrogen source is also your energy source and there is vast infrastructure for moving natural gas around. Building green hydrogen pipelines likely makes more sense than trying to backhaul electricity from diffuse sources. A single hydrogen pipeline can reify a lot of electricity production without the concomitant transmission and management infrastructure.
      • foobarian 2y ago
        A ton of hydrogen seems to occupy a cube with a 23 meter side. Wonder if a bunch of those could be built to hold the excess gas for night time operation. 100GWh is not small, but it's not impossible. The largest solar farm in operation is 5GW, and that could get you theoretically halfway there operating 10 hours a day. It feels like the challenges are a lot easier to solve than with fusion or nuclear.
        • lurk2 2y ago
          The issue doesn't appear to be storage, but transmission. Hydrogen can leak through metal and lead to it becoming brittle, so you can't use conventional natural gas pipelines to transport it.
          • foobarian 2y ago
            Exactly, these tanks can be giant balloons right next to the solar panels all feeding the in-situ ammonia plant.
            • lurk2 2y ago
              That was my thinking, but I think what he is saying is that power plants won't generate enough electricity to make building an in-situ ammonia plant economical. You need to network power plants together to operate a centralized ammonia plant 24/7, and the network to move this energy (whether in the form of hydrogen or electricity) doesn't currently exist.
              • foobarian 2y ago
                The land area of an all-in-one plant is maybe the biggest unknown for me with respect to just getting ownership and permits and such. But it's fun to imagine just picking a giant plot somewhere in the desert and plopping down 20 GW of solar panels, enough hydrogen storage to keep the less energy intensive steps operating throughout the night, and presumably batteries for whatever still requires electric power while panels are offline. Water and air in, sweet sweet ammonia out. :-) Cloudy weather would be an interesting problem I guess.