Factsheet Water Management in Electrolysis Plants
Electrolysis plants can be used to produce green hydrogen utilising electricity from renewable sources. From 2026 onwards, the first electrolysis plants on a 100 MW scale are expected to commence operation. In addition to renewable electricity, water is a crucial operating medium for these plants-used both as the substance split into hydrogen and oxygen, and as the coolant that removes process heat.
Is domestic hydrogen production’s water usage compatible with Germany’s available water resources, especially given the effects of climate change and recurring droughts? This factsheet provides an overview of the topic. Beyond this general consideration, water availability depends in particular on the location of the electrolysis plant and must therefore be assessed on a project-specific basis.
1. What is the water demand for hydrogen production via electrolysis? – An Example:
It is important to distinguish between water consumption and water use. Consumption refers to water being withdrawn from the local water cycle, whereas use means the water is returned in a controlled manner to the local cycle. The quantities required depend essentially on the type of cooling, water quality, and the electrolysis process, and can vary significantly.
Hydrogen Production with a 100 MW Electrolyser – Example:
Water consumption: 19 m³ of purified water per hour
Approximately 10 litres of water are consumed per kilogram of hydrogen, which has previously been demineralised and cleaned of all substances. A 100 MW electrolyser typically consumes around 19 m³ of process water per hour at full load, producing 1.9 tonnes of hydrogen per hour.
Water use: 5 m³ of process water from water treatment per hour (see also section 4.)
During the treatment of 19 m³ of process water from freshwater (e. g. groundwater or surface water), an additional 5 m³ of water per hour is required for process water treatment. This additional water absorbs the residual substances removed from the process water and is returned in a controlled manner to the local water cycle.
Cooling in a 100 MW Electrolyser – Example:
The process heat generated during electrolysis can, depending on the location, be used for local heating networks or must be dissipated by cooling systems. Several options exist for cooling, each with different water and energy demands. Whether they are suitable depends on the location of the electrolyser. One option is a wet recirculating cooling system, which is expected to be used in many planned large-scale electrolysis projects. Wet recirculating cooling systems function by spraying cooling water in a cooling tower, thereby releasing process heat to the surrounding air.
If a 100 MW electrolyser is operated at full load, this system requires around 76 m³ of cooling water per hour, which must be filtered before use. The breakdown is as follows:
Consumption in a wet recirculating system:
Approximately 51 m³ of water per hour evaporates during the cooling process and returns to the water cycle as precipitation, but not directly at the site.
Use in a wet recirculating system:
A further 25 m³ of water per hour is required for cooling but is subsequently returned to the local water cycle.
2. What is the expected total water demand for the electrolysis capacity planned in Germany?
Assuming 4,000 full-load operating hours per year, a 100 MW electrolyser consumes approximately 76,000 m³ or 76 million litres of purified water annually. The 10 GW of electrolysis capacity planned in Germany would collectively consume 7.6 million m³ of water per year. Surface water abstraction rates vary according to the flow conditions of the water body from which it is taken. When drawing water from a river or lake, abstraction (and thus production in the electrolyser) may need to be reduced to the environmentally safe and legally permitted level, especially during low water periods.
For comparison: According to the Federal Statistical Office (destatis), 176 billion m³ of water are available annually in Germany. In 2019, only 24.1 billion cubic metres were withdrawn for use, representing just 13.7 % of the total supply. If 10 GW of electrolysis capacity were installed, water consumption for hydrogen production would increase national water use by a mere 0.35 % compared to current levels.
A significant proportion of the planned electrolysis capacity will be installed offshore,
thereby reducing the share of water consumption from surface and groundwater sources.
3. What are the water demand implications for a project such as the planned 300 MW RWE electrolyser in Lingen?
RWE intends to extract water from the River Ems for electrolysis. The necessary water intake structure is already in place. If the planned 300 MW electrolysis capacity is operated for 4,000 full-load hours per year, a total of 1.2 million m³ of water will be required annually for production and cooling.
For comparison: The mean flow rate of the River Ems is approximately 80 m³ per second, resulting in around 2.5 billion m³ of water flowing towards the North Sea each year. Thus, the water demand of the 300 MW electrolyser amounts to 0.1 % of the available water in the Ems.
The water consumption for producing process water for hydrogen generation in a 300MW electrolyser, assuming 4,000 full-load hours per year, is around 228,000 m³. The water use for cooling – a wet recirculating system is planned in Lingen – is about 900,000 m³ per year, of which approximately 600,000 m³ evaporate via the cooling systems and around 300,000 m³ are returned to the Ems annually.(1)
For comparison: The water demand of Lingen’s approximately 60,000 inhabitants
is about 2.8 million m³ per year.(2) The river’s water level can fluctuate significantly throughout the year. To protect the water body, a minimum flow of the Ems must not be undershot due to ongoing water abstraction for electrolysis. If the flow of the Ems drops too low, water abstraction for electrolysis must either be stopped or compensated for, in accordance with the water law permit.
4. How is the process water treated?
Solid particles are removed from the cooling water by mechanical filtration. The process water required for electrolysis is physically purified and additionally demineralised so that only purified water is split in the electrolyser. During this water treatment process, only a portion of the water becomes purified water through demineralisation and physical filtration. This is 75-80 % for freshwater sources and 40-50 % for seawater. In addition, small amounts of salts are used as descalers in the cooling water circuit, and cleaning agents are used in water treatment. These process materials are approved for this use and have been tested for water compatibility.
5. What is the quality of the water released back into the water cycle after treatment and cooling?
a. Are foreign substances present?
The residual solution left after water treatment is released back into the local water
cycle as process water, together with wastewater from the cooling circuit. This
solution contains almost exclusively substances that were already present in the
source water. It may also include small residual amounts of the process materials
used. Continuous monitoring ensures that the returned water quantities are
compatible with water protection requirements.
b. How is it ensured that the water returned from the electrolysis plant is not too warm?
To protect water bodies and their ecosystems, the Surface Water Ordinance (Oberflächengewässerverordnung) stipulates requirements for the maximum temperature and permissible temperature increases for various types and states of surface waters. These limits must not be exceeded when discharging wastewater, to avoid negative impacts on water quality and aquatic life. Compliance is not determined solely by the discharge temperature, but also by the temperature after dilution. The potential for heating the water body and the environmental impact are assessed as part of the approval process; compliance with compatibility with water bodies must be demonstrated to obtain a discharge permit. Ongoing monitoring ensures that the requirements are consistently met.
6. What principles are used to assess environmental impacts?
The abstraction of water from surface or groundwater for hydrogen production requires a permit under the Water Resources Act, as does the discharge of wastewater.
As part of the permitting process, the impacts of water abstraction and discharge are comprehensively assessed to ensure that no adverse changes to the water body occur. In particular, the requirements of the Surface Water Ordinance and compatibility with the management objectives under the Water Framework Directive (Wasserrahmenrichtlinie) must be met. In addition, the requirements for nature and species conservation must be met.
(1) https://de.wikipedia.org/wiki/Ems mittlerer Durchfluss der Ems bei Versen (Nähe Meppen)
(2) calculation: 46.5 m³ per person per year
