In a new Nature Communications study, researchers propose a new method for hydrogen storage using existing pipes located at the bottom of lakes and reservoirs.
Hydrogen has surfaced as a promising alternative to fossil fuels for energy generation in several industries. The focus is especially on green hydrogen, which is produced via electrolysis of water using renewable energy sources like solar, wind, and air.
Nonetheless, the broad adoption of green hydrogen has faced challenges, primarily due to a lack of adequate storage solutions.
This study recommends the use of high-density polyethylene (HDPE) pipes as a means of storing green hydrogen. HDPE pipes are used at the bottom of lakes, reservoirs, or hydropower storage systems for water management.
Phys.org spoke to the study’s first author, Dr. Julian David Hunt, a Research Scientist at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.
He pointed out that his past work on compressed air energy storage (CAES) in the deep sea inspired his exploration of new strategies for hydrogen storage.
Limitations of current storage solutions
Several hydrogen storage options are available today, varying based on how the hydrogen is being stored.
As an example, compressed hydrogen needs to be kept in specialized tanks under high pressure, liquid hydrogen must be stored at extremely low temperatures, and underground storage solutions depend on the specific region.
With region-dependent solutions, such as salt caverns and depleted natural gas reservoirs, the method is not very scalable. This is because these resources may not be geographically available where hydrogen storage is needed.
Dr. Hunt and his team’s use of HDPE pipes is a more widely applicable method as these pipes are already present at the bottom of lakes, reservoirs, and other hydropower storage systems.
However, pursuing this option proved challenging because of the insufficient information regarding the underwater depths of ocean floors, riverbeds, lakes, and other water bodies.
Dr. Hunt said, “The main issue is the lack of bathymetric data of lakes and reservoirs. Essentially, this data represents a topographic map of the seafloor or lakebed, providing information about the shape, features, and composition of submerged areas.”
Purpose of HDPE pipes
The real purpose of the HDPE pipes is for water management in water bodies. They can be utilized to transport water for a variety of purposes, including agriculture, consumer needs, and drainage.
The material is made to withstand high pressures underwater, making it highly durable and it is also resistant to corrosion and degradation, making it suitable for long-term use.
Additionally, gravel is added around these pipes to ensure they are stable and don’t move due to water currents, acting as a support for the pipes.
These factors are also desirable if HDPE pipes need to be used for hydrogen storage.
HDPE pipes as storage
Hydrogen can be injected into these pipes from the top, pushing out the water into the pipes. Hydrogen needs to be stored at a certain pressure to avoid unnecessary expansion or compression. This is naturally achieved due to the pressure of the water column above the pipes.
By maintaining the internal hydrogen pressure at the same level as the water pressure outside, the system ensures that the hydrogen does not expand and exert stress on the pipes.
When water levels and, consequently, water pressure fluctuate, pressure relief valves are in place to adjust the flow of both water and hydrogen, thus maintaining a steady pressure in the pipes.
If heavy rain causes the water level to rise, this will lead to an increase in pressure. In such a scenario, pressure relief valves are used to withdraw hydrogen, letting in the excess water to maintain the pressure in the pipe.
This only works because hydrogen is insoluble in water, making this process harmless to aquatic life and minimizing environmental impact.
Endless possibilities
The researchers used data from the Oroville Reservoir in California to understand the potential of the proposed storage solution.
They found that the levelized cost of hydrogen storage using their proposed method came out to around 0.17 USD per kilogram at a depth of 200 meters in a year.
They further found that the method is more space-efficient than solar power generation, requiring about 38-times less area for storage than for solar panel installation.
In addition, this technology demonstrates great versatility, making it compatible with current hydropower infrastructure. It can also accommodate varying water levels in reservoirs, thereby increasing storage capacity when those levels rise.
The researchers also used data from artificial lakes and reservoirs.
The data indicate that the global capacity for hydrogen storage in lakes and reservoirs is estimated to be 15 PWh (petawatt-hours), comprising 12 PWh in natural lakes and 3 PWh in artificial reservoirs.
The Caspian Sea alone represents more than half of this potential (6.4 PWh).
“The possibility of storing hydrogen in hydropower reservoirs and lakes substantially increases the possible locations for large-scale hydrogen storage, particularly close to the demand for energy (cities, industrial districts) or renewable energy supply (solar, wind, and hydropower plants),” said Dr. Hunt.
Future hydrogen economy
“Hydrogen storage with gravel and pipes in lakes and reservoirs is a competitive alternative for long-term hydrogen storage and can support the development of future hydrogen economies,” explained Dr. Hunt.
Since the method uses existing infrastructure, it is cost-effective. Moreover, since hydrogen is insoluble in water, this approach poses no environmental risk.
However, Dr. Hunt pointed out, “The main environmental impact is the existence of large pipelines at the bottom of the lake/reservoir, which could disrupt the fauna and flora at the bottom of the reservoir.”
The lack of comprehensive data in this area is a bit of a problem, with Dr. Hunt hinting it could be an area of research he would like to explore.
“An interesting research [topic] would be to combine all the possible options for large-scale hydrogen storage in one database, including geological, reservoirs, lakes, and oceanic storage,” he concluded.
