Decarbonisation Technology - February 2024 Issue

Ultrapure water for electrolysis

Discover the mission-critical feedstock for MW- and GW-scale green hydrogen and ammonia projects of the future

Stephen B Harrison sbh4 Consulting

F or each kilogram of green hydrogen produced, 9-10 litres of ultrapure water are consumed by electrolysis. This equates to circa 200 litres of water per MW of electrolyser capacity. To generate that amount of ultrapure water, circa 1.5 times as much fresh water is required. Most large-scale green hydrogen projects are proposing to use renewable power generation from wind and solar resources. The optimum location for wind power generation is often offshore, and the best places to generate low-cost solar power are generally in arid desert locations. Neither location has unlimited access to fresh water, so seawater extraction and desalination will be required. To generate desalinated fresh water, approximately twice as much seawater is required. So, for each litre of ultrapure water, three litres of seawater must be extracted and processed. Seawater processing to ultrapure water will be an essential aspect of the MW- and GW-scale green hydrogen and green ammonia projects of the future. Desalination is key for electrolysis in arid locations with ideal wind and solar conditions Electrolysers are an expensive capital asset and represent a high portion of the capital investment for green hydrogen projects. Project economics can be improved if the electrolysers have a high utilisation rate, meaning they operate for many months per year and many hours per day. Integration of wind and solar can improve the firmness of renewable power generation. Hybrid schemes of this kind will be optimal in countries such as Egypt, Australia, Namibia, Oman, and Chile. However, these locations are not blessed

with abundant fresh water supply. Seawater extraction in many of these places is possible, but desalination adds to the cost and complexity of ultrapure water production. The technologies that will bring fresh water to electrolysis schemes are exactly those that are relied on today to make potable water available in arid locations. Desalination is used extensively in the Middle East to make water available for the emerging vertical farming sector and coastal cities. “ The technologies that will bring fresh water to electrolysis schemes are exactly those that are relied on today to make potable water available in arid locations ” Water tankers deliver fresh water to many villages in South Asia, and drilling for groundwater is common in inland locations without natural rivers. While the technologies are known, they must be adapted to make fresh water available for green hydrogen projects. Globally competitive green hydrogen and green ammonia production International competitiveness is essential for GW-scale projects that are being developed to produce green ammonia from green hydrogen as a clean energy vector for international trade. The market is global, and the customers are free to choose the lowest cost supplier. Shipping costs are small in comparison to renewable power generation and electrolysis costs, so optimal electrolyser utilisation and low-cost renewable power generation are essential.