The EU’s “Hydrogen Strategy for a Climate-Neutral Europe” of July 2020 is only the latest in a series of programs designed to foster the use of hydrogen to decarbonize and integrate the energy system. The G20, Germany, and Japan have also indicated interest in developing this technology. And more recently, a white paper jointly produced by German pipeline operators Nowega and Gascade and Siemens Energy studied practical aspects of converting natural gas pipelines as pillars of a future hydrogen-based energy transition.

Beside decarbonized hydrogen produced from natural gas, green hydrogen produced with an electrolyzer powered by sustainable electricity can be used for sector coupling (“Power-to-X”) and for the large-scale storage of renewable energy.

Green hydrogen is becoming economically more viable due to the declining costs of renewable energy as well as of electrolyzers. Linking up all elements of the energy system with hydrogen promises to deliver efficiencies, cut carbon emissions, and increase the robustness of energy systems while ensuring security of supply. In this context, one often-cited advantage is that the natural gas infrastructure could be reused with minor modifications for transportation and storage of hydrogen.

Pipelines for maximum energy density

Hydrogen can be transported as a gas in high-pressure containers, as a liquid in thermo-insulated containers, in processed form as methanol or ammonia, or in a chemical carrier medium. However, by far the most economically viable method is via pipeline, where a very high energy transportation capacity can be achieved.

The electrical transmission system is an important backbone for the transportation of renewable energy across countries. Ideally, this is complemented by the gas system: A standard pipeline can transfer up to ten times as much energy as a 380-kilovolt twin overhead power line with a rating of 1.5 gigawatts, at about one fourteenth of specific cost. But how much effort would be required to repurpose existing infrastructures to accommodate hydrogen?

With a dense nationwide pipeline infrastructure for natural gas, situated at the heart of the European energy system and long-distance transmission network, the German gas system offers unique opportunities to figure out how the most economic conversion of the gas infrastructure to hydrogen could work.

Well-developed existing infrastructure

With over 40,000 kilometers of long-distance transmission lines and more than 470,000 kilometers of distribution grid, Germany’s natural gas pipeline system is very well developed. Moreover, as a key transit country for gas supplies to its neighbors, it has the most expansive storage capacity of all EU members with a working gas volume of about 26.7 billion cubic meters and an infrastructure that’s well connected to the rest of the European gas market, making it a potential cornerstone of a sustainable and secure hydrogen energy system.

Christoph von dem Bussche is the CEO of Gascade, a German gas pipeline operator that manages a transmission system of about 2,900 kilometers, linked via major European transit pipelines to Russia and the North Sea ports. “The existing gas infrastructure is of very high value for the EU Hydrogen Strategy for a Climate-Neutral Europe,” he says. “First of all, constructing new infrastructure takes a lot of time. We can achieve our envisioned climate goals much faster using existing infrastructure. Second, using existing pipelines is very cost-efficient and can keep future energy prices low.”

Material testing: Can gas lines handle hydrogen?

But are pipelines and components designed for natural gas fully compatible with a changeover to hydrogen? Which, if any, changes are required?

At standard conditions, methane has three times the calorific heating value of hydrogen. Conversely, in pipeline systems, hydrogen with its smaller density shows a flow velocity that is up to three times higher than that of methane. This means that the same pipeline can convey three times as much hydrogen during a given period at the same pressure, while the energy transportation capacity is only slightly smaller.

Another factor is the integrity of the steel pipes and fittings. Depending on the quality of the steel and potential exposure to atomic hydrogen, in principle, embrittlement can accelerate propagation of cracks, reducing the pipeline’s service life by 20 to 50 percent. This is only likely, though, if the pipeline already has fractures and is subjected to dynamic stresses due to fluctuating internal pressure while at the same time being exposed to atomic hydrogen. The confluence of all three factors seems unlikely, however: Under normal operating conditions, there should be little load alternation, and only molecular hydrogen (H2) is conveyed.

Go with the flow: Compressing hydrogen for cavern storage

Some adaptations are nonetheless required. To compress the hydrogen to the operating pressure of the pipeline, compressor stations are required along the way. If hydrogen is mixed with methane and the existing compressors for natural gas are kept in place, some parts might need to be adapted, depending on the admixture of hydrogen. If the share of hydrogen exceeds 40 percent, the compressors will need to be replaced. A complete switch to a 100 percent hydrogen pipeline requires installing new and more turbines or motors and more powerful compressors to deliver the three-times higher volume flow of hydrogen compared to natural gas.

Since major milestones of such a large scale hydrogen energy system transition are not expected in Germany before 2030, the first pilots to convert existing pipelines to hydrogen duty are already under consideration and the hydrogen infrastructure should be built up in parallel with existing gas assets. In northern Germany, the long-distance gas network is complemented by vast underground storage facilities suitable for hydrogen. These aquifer and cavern reservoirs constitute nearly one quarter of Europe’s gas storage capacity – conveniently located close to the major ports and offshore wind parks on the North Sea coast.

A global hydrogen revolution is feasible

A shift toward a hydrogen-based energy system could be achieved fairly rapidly with only modest adaptations to existing transport infrastructures and hardware. In Germany, a number of companies and institutions have formed the GET H2 initiative to create a competitive hydrogen market and adapt the legal and regulatory frameworks. One of these is Nowega, a transmission system operator of about 1,500 kilometers of high-pressure natural gas pipelines. Nowega’s CEO Frank Heunemann believes that the German hydrogen strategy has set the right priorities. “Now it is important to set the concrete framework conditions as a basis for the development of green hydrogen as a fundamental element in the energy transition,” he says.

While subsidies can help make the first steps toward implementation economically feasible, stable political guidelines are needed if competitive companies are to develop this market in the long term, Heunemann believes: “In order to implement projects on an industrial scale using existing gas infrastructure, the legal foundation for hydrogen transport must be established in [Germany’s] energy legislation this year. It is only on this basis that companies can have a reliable long-term foundation on which to invest in development.” While the preconditions are especially favorable in countries such as Germany, the EU notes in its strategy document that other member states can also reduce investment requirements through the reuse of pipelines and storage facilities.

But if such a repurposing is possible in Europe, there is no reason why it should not also be feasible in other countries that have suitable infrastructure. “A changeover of the existing gas infrastructure for hydrogen supports the future sustainable energy supply with reasonable economic effort. And using existing infrastructure for new purposes as well makes sense in the light of a circular economy,” says Gascade CEO von dem Bussche.

Investing in hydrogen technology will not only help governments reach their climate goals, but also offers a potential course for economic recovery in a difficult global climate while preserving an edge in clean tech leadership. Giving gas pipelines the new purpose of transporting hydrogen is a realistic path toward achieving sound energy policy, environmental stewardship, and economic prosperity.