The use of hydrogen is among the key pillars of global decarbonisation, with many countries already publishing their strategies to support the mass production of the element. At present, most of the world’s supply of hydrogen is produced using fossil fuels, with significant associated carbon dioxide (CO2) emissions. But, in response to the call for a net-zero economy by 2050, energy companies and governments around the world have begun the drive toward cleaner supplies of hydrogen.
Achieving low- or zero-carbon hydrogen, however, is not without its difficulties. Chief among these is the potential for even greater competition for water sources. Michael Barlow, head of the environmental law team at Burges Salmon, says that there are several prevailing anxieties around water use for hydrogen production, stemming from pre-existing and growing concerns around water availability and quality.
Water is a finite resource that is very much under growing pressure. Only last summer, the UK and Europe experienced droughts in many regions, thus illustrating such pressure. Unfortunately, climate change means that water scarcity events are likely to happen more severely and frequently, which will also have a negative impact on water quality. Climate change, coupled with population growth and increased demands from other industries, means there will inevitably be great competition for water, and there is real concern than finding an effective balance across competing water needs will prove difficult, especially in already water scarce regions.
How is water used in the production process?
The means and amount that water is used in the hydrogen production process varies significantly based on the technology used, the source of the water and its quality.
Blue hydrogen largely uses natural gas in a process called steam reforming, which combines natural gas and heated water in the form of steam. The output is hydrogen and carbon dioxide, the latter of which is captured using carbon capture technology.
Alternatively, green hydrogen production uses water as a feedstock for electrolysis; a process where water is fed into an electrolyser, and an electrical current splits it into its singular components – oxygen and hydrogen.
“The data we have reviewed suggests that, on average, 20 litres of potable water are required for every one kilogram of hydrogen (kgH2) produced,” notes Barlow. “Data suggests that approximately half of that water is utilised in the chemical production of hydrogen and due to impurities and inefficiencies, half will be returned as wastewater post-production.
“With different qualities and compositions of water, those ‘water input’ against ‘water output’ ratio amounts are subject to change. For demineralised water, the amount of water required per kgH2 produced can be slightly lower. Conversely, seawater or poorer quality wastewater means that the amount of water needed will be a lot higher. Simply put, the higher the water quality, the better the ratio between water required and the amount of hydrogen that is produced.”
Additionally, thermal management may use significant volumes of water for cooling purposes, relevant for both blue and green hydrogen. Although other ‘dry’ cooling technologies are being developed by the industry, Barlow says that data emanating from industry indicates that it is a more energy intensive means of cooling compared to ‘wet’, albeit using a lot less water.
Alternatives to utilising potable water
Given the strain on water resources, particularly in areas of the world which experience frequent drought, utilising potable water for hydrogen production is a non-starter. Therefore, many green hydrogen producers are looking out to sea, or to wastewater, to provide the water needed for the electrolysis process. Such water inputs require treatment and desalination respectively, but, according to Barlow, will provide an additional water supply for hydrogen production in addition to, or instead of, mains water.
Hydrogen technology company, Logan Energy, has begun to use seawater to produce green hydrogen. Their project, ‘SEAFUEL’, located in Tenerife, uses between 200 and 300 litres of seawater which, once desalinated and demineralised, produces around 100 litres of purified water. That, in turn, produces approximately 10 kilograms of hydrogen a day, which has the potential to fuel 1000 kilometres of transportation.
“The beauty of seawater, of course, is that it is an almost infinite resource. More than 75 per cent of countries have direct access to seawater,” says Bill Ireland, chief executive at Logan Energy.
“Let’s say we live in Alice Springs, Australia, and there is a drought. You cannot tell people you are going to use what little water they might have to produce hydrogen, but equally, saving the water they do have and driving petrol tankers across the country to power transport and infrastructure has negative implications for the climate, ironically making more droughts likely in the future. Instead, you could transport three tankers of water to Alice Springs, use two tankers of the water to produce enough hydrogen to be able to power vehicles over the same distance as one tanker full of petrol would, and give the third tanker of water to the local community to help with the drought conditions.
“It is this kind of lateral thinking we need going forward, to join up different needs, and it is why I say we are not a hydrogen company, we are an energy solutions provider using hydrogen and other technologies like batteries to tackle the climate emergency in an economic manner.”
The challenge of desalinating seawater
Desalinating the water itself, however, can be an arduous and expensive process. Reverse osmosis is the most common method, consuming the least amount of energy when compared to other means.
After a series of pre-treatments removing larger impurities, the sea water is ready for reverse osmosis. At its core, reverse osmosis is a process that separates dissolved minerals and other impurities from water. Sea water is pushed through semi-permeable membranes under very high pressure, with the membranes acting like microscopic strainers which allow the smaller water molecules to pass through and leave behind salt and other minerals and impurities behind.
According to Barlow, one of the challenges that desalination presents relates to the large associated costs of developing the infrastructure and the cost of powering an energy intensive desalination plant. Large associated costs are currently a contributory factor why early developers are opting to use potable water as a feedstock. However, as the number of hydrogen production plants increase, and competition for high quality mains water intensifies, Barlow expects that desalinated water’s role in hydrogen production will grow.
“Additionally, from a logistical standpoint, desalination plants and treatment centres must be located by abundant water sources. Locational considerations are also required in securing a consistent supply of renewable energy, close to sources of wind or solar energy. The additional challenge of locating the desalination plant near the source of water is significant,” explains Barlow.
The hydrogen conundrum
Despite these considerations, the industry may still face questions over the coming years in regions where water is especially scarce. Justifying desalinated or treated water – at that point, good quality water – being used for hydrogen production rather than for other domestic or agricultural purposes may prove difficult. But, while blue hydrogen is less water intensive as a means of hydrogen production, the process still produces carbon dioxide (albeit usually with carbon capture technology). Green hydrogen, therefore, is still considered the ideal means of hydrogen production from a sustainability perspective.
As the World Economic Forum states: “In an era of water insecurity, it is crucial that the hydrogen industry makes it clear that it does not negatively impact water security or other water-heavy industries.” Being aware of the potential issues, and adapting to mitigate for them, is the first step.