The hydrogen economy - Where is the water?

“Green hydrogen”, i.e. hydrogen produced by splitting water with a carbon “free” source of electricity via electrolysis, is set to become the energy vector enabling a deep decarbonisation of society and a virtuous water based energy cycle. If to date, water electrolysis is considered to be a scalable technology, the source of water to enable a “green hydrogen” economy at scale is questionable. Countries with the highest renewable energy potential like Australia, are also among the driest places on earth. Globally 380,000 GL/year of wastewater is available, and this is much more than the 34,500 GL/year of water required to produce the projected 2.3 Gt of hydrogen of a mature hydrogen economy. Hence the need to assess both technically and economically whether some wastewater treatment effluent, are a better source for green hydrogen. Analysis of Sydney Water's wastewater treatment plants alone shows that these plants have 37.6 ML/day of unused tertiary effluents, which if electrolysed would generate 420,000 t H2/day or 0.88 Mt H2/year, and cover ∼100% of Australia's estimated production by 2030. Furthermore, the production of oxygen as a by-product of the electrolysis process could lead to significant benefits to the water industry, not only in reducing the cost of the hydrogen produced for $3/kg (assuming a price of oxygen of $3–4 per kg), but also in improving the environmental footprint of wastewater treatment plants by enabling the onsite re-use of oxygen for the treatment of the wastewater. Compared to desalinated water that requires large investments, or stormwater that is unpredictable, it is apparent that the water utilities have a critical role to play in managing water assets that are “climate independent” as the next “golden oil” opportunity and in enabling a “responsible” hydrogen industry, that sensibly manages its water demands and does not compete with existing water potable water demand.