Renewable electricity provides the energy for all processes described here. Depending on regional availability solar, wind, hydro or nuclear power can power the four key processes: desalination, electrolysis, air separation and Haber-Bosch.
Unless sufficient fresh water is available, sea water can be processed to a quality sufficient for electrolysis. For each kg of ammonia approximately 1.6l of water are needed. With Reverse Osmosis, the electrical energy required for 1t of ammonia is less than 1 kWh.
Electrolyses split the water into hydrogen and oxygen. The oxygen itself has potential value and could feed into processes not considered here. To produce 1t of hydrogen approximately 50MWh are required. The cost of the electrolyser itself is expected to fall from around $900 to as little as $400 in the next 10-20 years if GW scale is achieved. (Saba, 2018)
The nitrogen needed for the ammonia generation is readily available from the ambient air, which consists to 78% of nitrogen. A tonne of nitrogen requires 80kWh of electrical energy.
The Haber Bosch process converts nitrogen to ammonia by a reaction with hydrogen using a metal catalyst. A tonne of ammonia requires 176kg of hydrogen and 824kg of nitrogen. Electrically driven Haber Bosch processes can produce a tonne of ammonia from 1.16MWh. (Smith, 2020)