By Gavin Bollan , Technical Director, ITPEnergised
Hydrogen is increasingly being hailed as a vital part of the solution that will help solve the global climate crisis. New green hydrogen projects (hydrogen produced from renewable electricity generation) are being created at an unprecedented rate and the global 2040 target capacity for green hydrogen is more than 200 GW.
However, sustainability should be a holistic consideration that considers all outputs from the system. If the balance is tipped and ‘green’ takes on a murky tinge because the overall process to create green hydrogen can prove damaging to the environment, then its environmental credentials may not be as commendable.
So, while officially speaking, it could arguably still be called ‘green hydrogen’, if the process is causing aquifer depletion or groundwater pollution because of how the feed water is extracted or the effluent is being disposed of, then it does somewhat undermine its environmental benefits.
This would be a case of partially solving a problem only to create another, possibly even greater one.
Huge volume of water required
To achieve the 2040 green hydrogen target, we would need 1.7 million cubic metres of fresh
water per day. With water becoming increasingly scarce , and the sheer amount of energy required to process this volume of water, it begs the question of whether ‘green hydrogen’ is less sustainable than its name might imply?
Green hydrogen currently requires very pure water, from which most, if not all, of the salts have been removed. This is achieved through a desalination process, which, if hydrogen is to continue to grow at its current trajectory, needs to be able to significantly increase its capacity.
The challenge of disposing of reject brine
The more impure the feedstock (or water source) is to begin with, the more waste will be produced. Seawater, for example, has to go through an intense desalination process to separate the pure water from the dissolved solids. As the demand for pure water increases, the issue of what to do with the waste product intensifies. Developers of green hydrogen projects are faced with the challenge of what to do with the reject brine and how to dispose of it responsibly.
For example, disposing of hypersaline discharge into a constrained environment, such as hot, shallow seawater could lead to a build-up that would be beyond the tolerance levels of plants and animals living in that environment.
It is crucial therefore that responsible developers think creatively when it comes to disposal and seek expert advice .
Where there is enough room to do so (such as in large desert areas), effluents can be concentrated to a very high level of dissolved solids and stored in a holding vessel on land — a salt pan, effectively — and left to evaporate. There would still be the residual salt to deal with in time, but this may be preferable to relying on the sea as a sustainable disposal route.
This method of effluent management requires heat, space and sunshine, which are not often in great abundance in many locations in the world, therefore this method of effluent management does not present a widespread solution.
For green hydrogen to be sustainable, the environment that receives the waste product from the electrolyser feed water treatment system, be it land, sea or another watercourse, must be able to accommodate the effluent without adverse effect. That is what developers will need to focus on and the impact of which they will need to evaluate.
Substantial use of energy
There is also the issue of energy usage. As noted above, when the feedstock is seawater, a substantial amount of energy is required to perform desalination.
The hydrogen production process, including conditioning, drying, compressing and storing, can be power-thirsty, even before the energy required to purify feed water is considered. The system needs to be designed to be as energy efficient as possible to maximise the hydrogen output and so as not to waste excessive energy through running the hydrogen plant. It is important as it will also impact on the economic viability of the project.
More efficient technology may be on the horizon
Technology of the future may well be able to ease the current challenges facing hydrogen production. For example, a combined desalination-electrolysis system is currently being developed in China. The process uses a low-energy method to purify seawater through novel membrane technology.
While innovations such as this are heartening and could reduce the overall energy consumption per quantity of hydrogen produced, they do not yet solve the key problem of how to deal with the waste brine. This technology is still at the research stage, but it would need to prove scalable and cost-effective to make it an attractive alternative to pure water electrolysis.
Although pressures on the desalination market are already showing signs of increasing as the world demands more green hydrogen, the conversation around the sustainability of the practice has yet to keep pace.
Expect tighter regulations and environmental assessments
There is no doubt, that the noise around the responsible disposal of liquid waste effluent from green hydrogen production will gain volume as demand increases still further. When this happens, my prediction is that awareness will grow, and correspondingly environmental assessment requirements will increase and regulations will tighten, meaning that developers will need to be extra vigilant to ensure they comply . Additionally, those who are against the use of green hydrogen, may also see this as an opportunity to undermine its value.
If the production of hydrogen is to be both green and sustainable, developers will need to consider new and innovative disposal methods and ensure they can respond with confidence when customers and regulators insist on accountability.