サステナビリティ
海水から得られる水素と淡水？太陽エネルギーによる解決策が登場
Securities.io を Google の優先ソースに追加
水と水素の需要に応える
Among the most required resources in many regions of the world with growing populations is freshwater. This is a growing concern, and potentially a factor of geopolitical instability, with, for example, the discussion of who gets to use the Nile River’s waters almost bringing Egypt and Ethiopia to war.
While desalination methods are becoming more common, they are very energy-intensive, and even mass deployment of solar panels is often not enough.
Another thing we need is more renewable energy in a form that can be stored away and used as a fuel for heavy-duty equipment and industry. In theory, hydrogen would be a good option, but it has so far failed to be deployed at scale due to too high costs.
Here, too, solar power can help, but the cost of hydrogen production through electrolysis has limited its use.
It seems that both problems could be tackled at once by a new solar-powered electrolysis technology, using not fresh water, but seawater. It is even producing fresh water as a by-product of its hydrogen generation.
It was invented by researchers at Johns Hopkins University, Michigan State University, Cornell University, Lehigh University, and MIT, who published their results in the journal Energy & Environmental Science, under the title “Over 12% efficiency solar-powered green hydrogen production from seawater”.
海水を有効活用する
Seawater is maybe the most abundant resource on Earth, covering 70% of the planet’s surface. It is also easy to access for most of the world’s population, as more than 40% live in the 100km range (62 miles) from the nearest coast, and more than 50% in the 200km range (124 miles).
出典: StatsMapsNPix
“That’s why we came up with this technology. We thought, ‘OK, what is the most abundant resource on the Earth?’ Solar and seawater are basically infinite resources and also free resources.”
Unfortunately, seawater is salty and unsuitable for both human consumption and the irrigation of crops. This is why alternative supplies of fresh water in dry regions are being considered, like 大気水収集 or 廃水の高度処理.
Still, desalination is likely the only durable solution at scale for supplying abundant water to many countries. As those countries are also often in sunny regions, solar-powered desalination, either 太陽光淡水化 or direct evaporation, is a potential solution. The fixed costs of these systems, however, are making the production of water rather expensive.
“Water and energy are both critically needed for our everyday life, but typically, if you want to produce more energy, you have to consume more water.
On the other hand, we need drinking water, because two-thirds of the global population are facing water scarcity.”
As a side note, seawater is also not a suitable source of material for hydrogen generation, which requires ultra-pure (distilled) water.
太陽光のより効果的な利用
So far, the economics of desalination has hit the problem that you need to build large and expensive solar collecting facilities while trying to produce water as cheaply as possible.
What the researchers of this study did was to make these facilities produce something more valuable (hydrogen) while also making water at the same time.
As a rule, photovoltaic installations can only utilize a portion of the solar output, as 100% efficiency is impossible, and some of the wavelengths are too short or too long to be used by the panels’ silicon.
This leaves a lot of solar energy wasted in photovoltaic facilities. Worse, this solar energy generates heat, which further reduces the efficiency of the solar panels (most designs work best below 30°C (86°F).
すべてを同時に実現する
As these problems seem impossible to solve separately, at least in a way that is economically competitive, maybe the solution is a more holistic approach. It was with this concept in mind that the researchers considered potential synergies if the same device produces at the same time power, hydrogen, and freshwater, using only sun and seawater.
The design they conceived looks to solve every problem at once, by making each limitation of a given sub-process the solution for another problem:
- Hydrogen and freshwater production is done in the same device, to share capital costs and utilize the full solar spectrum.
- The water comes from seawater, removing resource constraints for hydrogen production.
- The production of ultra-pure freshwater absorbs heat, keeping the solar panels cool and increasing electricity production.
- Seawater never comes into contact with the electrocatalyst, producing hydrogen, removing problems of corrosion and unwanted chemical reactions.
- As the power is directly utilized for hydrogen production in the same device, there is no need for batteries, upgrades to the power grid, etc.
先進的な製造
While looking simple in concept, managing to perform efficiently all these operations at once is a real engineering challenge.
The evaporator and PEM electrolyzer are separated by an air gap, which avoids direct contact between seawater and electrocatalysts.
A few other features were added to improve the design:
- Using a capillary wick that traps the water into a thin film that is in direct contact with the solar panel to allow it to cool the solar panel with evaporation.
- Leverage the thermal effect to increase vapor pressure, a must for higher production rates of distilled water and efficient hydrogen generation.
- Using the energy released by the vapor-to-liquid phase change to improve hydrogen production efficiency.
- Using unilateral seawater flow to avoid salt accumulation, is a permanent issue for all desalination systems.
At the end of the process, slightly more salty seawater can be sent back into the sea, and distilled water that has not been turned into hydrogen can be used as clean drinkable water.
“The design was challenging because there’s a lot of complex coupling: desalination coupled with electrolysis, electrolysis coupled with the solar panel, and the solar panel coupled with desalination through solar, electrical, chemical, and thermal energy conversion and transport.”
プロトタイプのテスト
When testing their hybrid solar distillation-water electrolysis (HSD-WE) device, the researchers found that the small 10 cm x 10 cm cell could produce 200 milliliters of hydrogen per hour, with 12.6% energy efficiency, directly from seawater under natural sunlight.
The test was performed outdoors, with real seawater and realistic weather conditions, notably with cloudy weather reducing the hydrogen output at one point of the day.
経済的実現性
The researchers calculated how much hydrogen would be produced by their prototype in various locations. When compared to the current average of $10/kg for green hydrogen, it is clear that it a lot more efficient past the first year of operation, falling to $5/kg with three-year operation and $1/kg with 15-year operation.
This is because traditional green hydrogen costs are quickly plateauing, constrained by energy and capital costs.
In comparison to the classical electrolyzer, the HSD-WE is mostly passive and gets its energy from the sun directly, without extra capital costs of connection, water transport, storage, etc.
“We want to avoid carbon emission, avoid pollution. Meanwhile, we also care about the cost, because the lower the cost we have, the higher the market potential for large-scale adoption. We believe there is a huge potential for future installation.”
企業 水不足を解決する
XYL 価格チャート
Together with the European Veolia, Xylem is a global leader in water purification, wastewater treatment, and desalination. It employs 23,000+ (of which 6,000+ engineers) people and operates in 150 countries, with a focus on the USA, with 35,000+ direct industrial customers.
Its main market is municipal drinking and wastewater, but it also provides dedicated solutions to other sectors like healthcare, power, food & beverages, oil & gas, microelectronics, etc.
出典: Xylem
Xylem can provide the critical patented pieces of equipment to clean or produce water like ozone generators, UV lamps, desalination membranes, ultra-pure water generators, etc. But it also provides “simpler” equipment equally critical to water-related operations like turbines, pumps, piping, injection, software, etc. as well as maintenance, repair, and installation services.
出典: Xylem
The water market is still a very fragmented one, with Xylem one of the largest companies in the sector but still holding “only” a 10% market share out of its $80B served addressable market.
The company spends around 4% of its sales on R&D. It should benefit from new regulations regarding PFAS (Per- and polyfluoroalkyl substances, or forever chemicals), with 6,000+ utility facilities needing such PFAS treatment.
Overall, this makes the company’s investing profile less like that of an industrial company (often cyclical) and more like that of a utility company growing with the overall economy or a little bit above that rate, like most of its consumers.
Xylem Inc.の最新情報
参照された研究：
1. Xuanjie Wang, et al. (2025) “海水からの12%以上の効率で太陽光駆動グリーン水素生産”。 Energy Environ. Sci., 2025, Advance Article. https://doi.org/10.1039/D4EE06203E
