By Irina Slav
Gigawatt upon gigawatt of green hydrogen capacity is being planned across Europe, Asia, and Australia. According to proponents of the technology, green hydrogen – the kind produced through electrolysis powered by solar, wind, and other renewable energy sources – is the best way to decarbonize heavy polluter industries. There is much talk about the falling costs of solar and wind and how they will make green hydrogen viable very soon. What nobody seems to want to talk about is water. Electrolysis is the process of breaking down water into its constituent elements – hydrogen and oxygen – using an electric current. The process is performed in an installation called an electrolyzer. When hydrogen advocates talk about the bright future of the technology, they focus on the costs associated with the electricity needed for the electrolysis. But electrolysis, besides electricity, needs water.
Tons of water – literally.
One industry source told Oilprice that the production of one ton of hydrogen through electrolysis required an average of nine tons of water. But to get these nine tons of water, it would not be enough to just divert a nearby river. The water that the electrolyzer breaks down into constituent elements needs to be purified
The process of water purification, for its part, is rather wasteful. According to the same source, water treatment systems typically require some two tons of impure water to produce one ton of purified water. In other words, one ton of hydrogen actually needs not nine but 18 tons of water. Accounting for losses, the ratio is closer to 20 tons of water for every 1 ton of hydrogen.
Speaking of water purification, organic chemists explain that the simplest way to do this is by distilling it. This method is cheap because it only needs electricity, but it is not fast. Regarding the electricity cost, distilling a liter of water requires 2.58 megajoules of energy, which translates into 0.717 kWh, on average.
This doesn’t look like much at first glance, but let’s see how things look on a larger scale. Germany is the country with the most ambitious plans for green hydrogen. The cost of electricity for non-household users in Germany was an average of $0.19 (0.16 euro) per kWh as of last year. At a power consumption rate of 0.717 kWh, the distillation of a liter of water, then, would cost $0.14 (0.1147 euro). For a ton of water, that would be $135.14 (114.72 euro).
However, electrolysis needs as much as 18 tons of water – not accounting for losses during the process – to produce one ton of hydrogen. That means that the cost of water purification for the production of a ton of hydrogen would be $2,432 (2,065 euro). This is based on the assumption that the water would be purified using the cheapest method available. There are other – much faster – methods, but they are also costlier, involving ion exchange resins or molecular sieves.
Other alternatives to distillation, according to chemists, are unreliable at this point.
So, providing the right kind of water for hydrolysis costs money, and while $2,400 per ton of hydrogen may not sound like much, the cost of purifying water is not the only water-related expense in the technology that seeks to make hydrogen from renewable sources. Besides being pure, the water to be fed into an electrolyzer has to be transported to it.
Transporting tons upon tons of water to the site of an electrolyzer means more expenses for the logistics.
To cut these, it would make sense to pick a site where water is abundant, such as by a river or the sea, or, alternatively, close to a water treatment facility. This puts a limit on the choice of locations suitable for large-scale electrolyzers. But since an electrolyzer, to be green, needs to be powered by renewable energy, it would also need to be in proximity to a solar or a wind farm. These, as we know, cannot be built just anywhere; solar farms are most cost-effective in places with a lot of sunshine, and wind farms perform best in places where there is sufficient wind.
Needless to say, these places are not, as a rule, close to waterways, except offshore wind, which seems perfect for the production of green hydrogen. Unfortunately, offshore wind is also the costliest form of the three renewable sources – solar, onshore wind, and offshore wind – normally mentioned in the context of green hydrogen production. According to Rystad Energy, the capital costs of an offshore farm are twice as high as those of its onshore counterpart and four times as high as the costs of a comparable solar installation.
Not all costs associated with the production of hydrogen from renewable energy sources are the costs of those renewable energy sources. Water is the commodity that the process needs, and it is a little odd that nobody seems willing to discuss the costs of water, including the European Commission’s Green Deal Team.
Perhaps the cost of water supply, storage, and purification is negligible compared with other costs that need to be addressed first. Yet it is an actual cost that should be added to the total when estimating how far the technology of producing hydrogen from renewable electricity has progressed and how viable it has become.
For now, experts appear to be unanimous that it is not viable – not without significant government support.