Through this article, Designolle emphasizes the critical role of safe, scalable hydrogen storage solutions like Vallourec’s Delphy vertical underground system in enabling the reliable integration of hydrogen into the renewable energy mix and supporting the global energy transition.
Hydrogen is becoming an increasingly important part of the renewable energy mix. From production to end use, safe hydrogen storage is needed to ensure a reliable supply along the value chain. Vetted and tested for commercialization, Vallourec’s Delphy underground vertical storage system provides a scalable solution with a capacity range from one to 100 metric tons.
There are promising signs worldwide that hydrogen will play a big role in the energy transition. The Hydrogen Council recently reported a 90 percent increase in investment in projects that passed the final investment decision (FID) in 2024 compared to 2023. This represents a cumulative 4.6 Mt p.a. of clean capacity past FID (up 53 percent from 2023). The positive upswing is partially due to supportive policies and action plans being designed and implemented globally. In February 2025, the European Commission notably published its strategy to foster its regulatory framework and investment program for low-emissions hydrogen production.
This decarbonization journey involves green hydrogen development, utilizing renewable energy to power the electrolysis process. However, renewable energy, such as solar and wind, only offers intermittent hydrogen production through electrolysis. In contrast, hydrogen end users need a continuous and reliable supply for processes like refining ammonia and e-fuel production. To manage intermittent production and effectively integrate hydrogen into a future decarbonized energy mix, large-scale hydrogen storage is the key.
What is Vertical Hydrogen Storage?
Until recently, hydrogen storage was limited to small-capacity cylinders or bullet tanks holding up to one metric ton or vast spaces like salt caverns, offering up to 10,000 metric tons of storage capacity. Vertical underground hydrogen storage, such as Vallourec’s Delphy solution, fills the gap, providing a viable, secure and scalable option for onsite storage from one to 100 metric tons.
“Vallourec partnered with third-party certification expert DNV to accompany its technology qualification process according to DNV’s Recommended Practice RP A203. This process addresses all potential risks and tests and validates the technology’s entire storage system architecture”
Leveraging Vallourec’s 50-plus years of metallurgical expertise, the pressure vessels are designed using special alloys that resist hydrogen embrittlement. Vallourec’s range of hydrogen-proof premium connections ensures a tight system assembly.
Vertical storage offers a flexible solution that can be easily installed at facilities where surface area is at a premium. Delphy requires 30 times less acreage than an above-ground alternative. And because it is a modular solution, its storage capacity can be optimized according to project needs.
Focus on Safety
Delphy, above all, is a safe hydrogen storage system. Throughout its development process, safety has been at the forefront. Vallourec partnered with third-party certification expert DNV to accompany its technology qualification process according to DNV’s Recommended Practice RP A203. This process addresses all potential risks and tests and validates the technology’s entire storage system architecture. The qualification plan was defined (Statement of Endorsement reached in 2024) and testing took place on a demonstrator built at Vallourec’s research facilities in France. Vallourec and DNV are currently reviewing the test results, targeting a full technology qualification by mid-2025.
This follows a regulatory compliance assessment, specifically the European Pressure Equipment Directive (PED). In 2024, a third-party inspector reviewed the demonstrator’s design and manufacturing. After the pressure test, the inspector confirmed compliance with the PED—a mandatory step before Delphy can be put on the market.
The system’s intrinsic safety comes from the pressure vessels’ design, subsurface geometry, and passive safety features implemented in the design. Its state-of-the-art instrumentation and automation provide further safety assurance, with various detection systems that react to potential leaks or hazardous events.
Vallourec joined with experts from third-party classifier Bureau Veritas to perform a comparative quantitative risk assessment. The test concluded that Delphy’s safety perimeters are half of what equivalent above-ground options need to ensure safe distance. This benefit is a strong asset in easing integration into industrial sites and during the permitting process.
Delphy Storage Unlocks Value: Case Study for Green Ammonia Projects
Italian technology and engineering group NEXTCHEM (part of the MAIRE group) and Vallourec assessed the integration of Delphy storage into hydrogen and green ammonia production projects around the world. They ran a case study on a typical project and compared several scenarios. The study determined that integrating Delphy hydrogen storage with green ammonia production could significantly reduce the levelised ammonia (LCOA) cost by up to 15 percent.
Accelerating Toward Commercialisation
With technology validation well underway, Vallourec stands ready to support hydrogen market development worldwide. It is targeting Delphy’s first commercialisation in 2025 as part of its strong ambitions to develop its businesses in New Energy sectors.
