Green Hydrogen and Water – It’s all about location
Location is everything in green hydrogen production. There must be a source of consistent, abundant green energy to power its electrolyzers, as well as a reliable water supply for the hydrogen creation process. The best source of energy for these facilities is usually solar – but, typically, good places for solar farms do not have a steady supply of water. Most PV projects are being built in arid areas, meaning abundant solar power but pre-existing water stress.
Luckily, there is a possible solution: desalination. This process supplements the water supply needed to produce hydrogen in places that do not have a readily available source of freshwater. Desalination, sometimes denoted as ‘desal’ or ‘de-sal,’ takes seawater and uses reverse osmosis to remove the salt from about 50% of it, then sends the remaining 50%, now extra-salty water known as brine, back into the ocean. Originally used to supplement drinking water, desal has been around since the 1960s and has grown steadily in the last few decades . It has since become important to green hydrogen projects as a way to supplement or replace local water resources in H2 production.
Desalination has received some pushback stemming from its energy intensive nature and concerns about harm to sea life. However, there are emerging solutions to these challenges:
- Desalination is seen as energy intensive, and therefore is thought to add significant costs to hydrogen production. Yet around 80% of the cost used to make hydrogen goes toward energy for electrolysis, making desalination a small part of the energy use and cost of the project. In fact, desalination is actually a very valuable source of water for production facilities in remote areas or on the coast, and even with the small additional cost, targets such as the DOE’s plan to get H2 under $2/kilogram would still be in reach.
- Typically, water is gathered for desalination using an intake pipe that sits on the sea floor. This situation can be problematic—if the water is sucked in too quickly, large organisms like fish can get stuck on the pipe’s screen, leading to injury or death. Also, small organisms like fish larvae and plankton can pass through the screen and are later killed during the water filtering processes before reverse osmosis. Recently, practices have been put into place to resolve these issues. For example, facilities have decreased the speed of their intake process to allow fish to swim against the current so they do not get trapped. Another strategy that is gaining momentum is putting the intake underneath the sea floor and using the ocean’s sand as a natural filter to protect small organisms.
- At the other end of the process, brine is released back into the ocean. If done improperly, the water in the area where the brine is released could become extra salty and lower water oxygen levels, which can be detrimental to marine life near the release pipe. However, there are strategies that can decrease the likelihood of this problem occurring. For example, seawater can be added to the brine before being released back into the ocean to lower the salinity level and minimize the byproduct’s impact. Alternatively, brine can be pumped back into the ocean at a speed fast enough to spread it across a large area, preventing it from overwhelming a small section of the sea with its salinity.
Given these points, desalination can be a great way to provide water needed to produce green hydrogen. The costs and energy usage do not add enough to the overall project to be detrimental, and processes have and will continue to be developed to negate potential environmental concerns surrounding desalination plants. In fact, desalination and hydrogen production paired together can have some additional positive environmental effects—to learn more about one of them, check out this article about efforts to reoxygenate the ocean with oxygen produced during electrolysis.
Additional reading list:
As Water Scarcity Increases, Desalination Plants Are on the Rise (YaleEnvironment360)
Desalinated ocean water for green hydrogen production (pv magazine)
Does the Green Hydrogen Economy Have a Water Problem? (ACS Energy Letters)
Explainer: How does a desalination plant work? (Cosmos)
Seawater Desalination (San Diego County Water Authority)
