The “energy transition” has a long tradition in Öhringen: As early as 1910, 29 municipalities in the Hohenlohe region joined forces to found the “Überlandwerk Hohenlohe-Öhringen” and electrify the villages and towns in northern Baden-Württemberg. This pioneering spirit is still alive and well more than 110 years later: In Öhringen, the successor company, Netze BW GmbH, transported up to 30 percent hydrogen via the local natural gas network for the first time. This hydrogen is produced via electrolysis by the contracting division of EnBW Energie Baden-Württemberg AG.
While the diesel generator hall features a neoclassical architectural style with Art Nouveau elements, the hydrogen plant built right next to it has a rather austere appearance. The only clues to the high-tech equipment installed inside the two white-painted 40-foot containers are the numerous lightning rod antennas: ahydrogen electrolyzer and a gas mixing plant.
Nevertheless, the gas distribution network operator is proud of the project: “We were able to demonstrate that a mixed gas of hydrogen and natural gas can be used without any problems to heat buildings,” explains project engineer Daniela Wieland, who works in the “Technology and Innovation” division at Netze BW to advance the energy transition.
Heating and Cooking with 30 Percent Hydrogen
About 30 households in Öhringen were “disconnected” from the existing gas grid for two heating seasons in 2022 and 2023. Instead, they heated their homes and cooked with natural gas blended with up to 30 percent hydrogen by volume—and the first “hydrogen island” was born.
“Water electrolysis is one way to store excess renewable electricity,” explains Wieland.
Water electrolysis is a relevant option in the energy transition because renewable energy sources such as wind and solar power are not available continuously: Since electricity cannot yet be stored on a large scale, wind and solar power plants currently often have to be curtailed to prevent the power grid from becoming overloaded. This is where hydrogen comes in as a storage medium: Through electrolysis, excess electricity can be used to split water into hydrogen and oxygen. The hydrogen produced in this way can be stored and, when needed, either used directly as fuel or converted back into electricity through re-electrification.
But can existing natural gas pipelines even be used to transport hydrogen or natural gas-hydrogen mixtures? How does the mixture behave in the pipelines and as a fuel gas? And how safe and reliable is the necessary technology in everyday use? “These questions cannot be answered theoretically—a large-scale trial is needed,” explains Wieland.
The hydrogen is produced in Öhringen using an alkali electrolyzer © VEGA Grieshaber KG
To find answers, Netze BW has embarked on this experiment in collaboration with Öhringen residents, burner manufacturers, researchers, local tradespeople, and other stakeholders. The field test begins with electrolysis and the blending of hydrogen into natural gas. At Netze BW’s facility in Öhringen, the hydrogen is produced in an electrolyzer manufactured by Hydrogenics. The system, housed in the first container, includes a water treatment system using reverse osmosis as well as four electrolyzer stacks. The second container houses the gas blending system, which is used to blend hydrogen into natural gas in defined proportions.
Measurement technology ensures the right mixture
Measurement technology plays a central role in the blending plant: flow, pressure, and temperature must be monitored with high precision. This is because one technical challenge is ensuring the safety and efficiency of the plant across varying hydrogen concentrations. Hydrogen has different physical properties than natural gas, such as a higher flame propagation speed and lower energy density, which requires adjustments to gas processing and combustion technology. These factors make the monitoring and precise measurement of the gas mixture and operating parameters particularly important.
Daniela Wieland, an engineer at Netze BW, explains how the blending plant works, where hydrogen is blended with natural gas © VEGA Grieshaber KG
The measuring instruments used in hydrogen applications must be able to withstand specific challenges—because hydrogen has certain physical and chemical properties and, in some cases, must be produced, stored, and processed under extreme operating conditions.
VEGA Measurement Technology Meets Hydrogen Requirements
VEGA offers a range of innovative technologies designed to address the specific challenges of hydrogen applications. The company uses durable materials such as special stainless steel alloys—including 316L—and coated materials that are less susceptible to hydrogen embrittlement —for example, in the VEGABAR 83. Gold and gold-rhodium coatings on the measuring diaphragm also provide protection against diffusion.
Ceramic measuring cells are ideal for applications where durability and exceptional pressure resistance are essential—such as in natural gas applications. The VEGABAR 82, with its oil-free ceramic measuring cell and high overload capacity, is a suitable sensor for many processes—including pressure monitoring in hydrogen pipelines. Due to their increased chemical resistance, these sensors are also used with aggressive media such as the potassium hydroxide solution used in electrolysers.
Precise Pressure Measurements During the Blending of Natural Gas and Hydrogen
VEGA’s measurement technology also plays a role in the implementation of the hydrogen island. The devices help ensure that the blending plant operates safely and efficiently. The sensors and measurement systems used in Öhringen monitor various critical parameters and enable precise control of the hydrogen-natural gas mixture. The blending plant consists of several components that ensure the two gases are mixed safely.
The pressure readings are displayed on-site and also transmitted to the higher-level control system © VEGA Grieshaber KG
Natural gas and hydrogen are fed into the mixing plant separately. While the hydrogen from electrolysis enters the plant at pressures between 3 and 10 bar, the natural gas arrives at a pressure of up to 13 bar. For precise control, it is necessary to determine the standard volumetric flow rates of hydrogen and natural gas. To do this, the measured operating volumetric flow rates are used, along with sensors that measure pressure and temperature. The reference variable of the control system is the hydrogen content in the mixed gas. This is primarily determined by calculating the ratio of the standard flow rates at the gas meters.
Any significant deviations from the set hydrogen concentration are monitored using the mixed-gas meter, which is also installed in the system (standard flow rate of hydrogen + natural gas = mixed gas). If this flow ratio deviates, the mixed-gas line is shut off. The hydrogen concentration is continuously monitored using a gas quality analyzer from Mems AG. In this way, the hydrogen is metered and fed into the mixing section, where it is homogeneously mixed with the natural gas. Various safety mechanisms in the plant control system, as well as safety shut-off valves, ensure that the plant operates safely and efficiently.
Even after mixing, the standard volume flow is calculated based on the operating volume flow, pressure, and temperature, and is then fed into the low-pressure network (70 mbar) and the medium-pressure network (700 mbar) via a buffer tank. The pressures are monitored here as well. The VEGA pressure sensors used in Öhringen, such as the VEGABAR 82, feature increased precision and long-term stability. With their ceramic measuring cell, they also offer high durability. Furthermore, the sensors enable robust pressure monitoring, even under varying operating conditions, which is necessary for the safe and stable operation of the mixing plant.
100 Percent Hydrogen in the Future
“The Öhringen Hydrogen Island project has already yielded important insights,” Wieland summarizes. “Blending hydrogen up to a concentration of 30 percent by volume proved to be technically feasible; no adjustments to the infrastructure itself were necessary. Only a few heating units at customers’ sites had to be replaced.” VEGA’s measurement technology played a key role in monitoring and optimizing the plant, enabling safe and efficient operation.
The measurement results showed that both the gas network and the household appliances operated reliably, even with higher hydrogen concentrations of up to 30 percent by volume in the gas mixture. In addition, the increased accuracy and reliability of the VEGA measuring instruments proved to be beneficial. This makes it possible to control the system even under dynamic operating conditions.
And so the NETZlabor Öhringen Hydrogen Island project is providing important insights for the further development of the hydrogen economy. “It has shown that existing gas infrastructures can be adapted for operation with hydrogen at minimal cost,” says Wieland.
In the long term, the project is intended to help develop new business models for the hydrogen economy and advance the integration of renewable energy into the heating supply. In a follow-up project, Netze BW plans to heat its own office buildings in Öhringen exclusively with 100 percent hydrogen by volume produced through electrolysis. The heating systems are currently being retrofitted for this purpose. Here, too, VEGA’s measurement technology will continue to play a key role in ensuring the safety and efficiency of the systems—thereby helping to advance the energy transition not only in Öhringen but beyond.
