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New approach for energy storage

The power-to-gas energy storage process from ETOGAS offers a compelling approach to what is currently the greatest challenge of the energy transition: the storage of renewable energy. Siemens has supported the company in Stuttgart from the beginning and is supplying reliable and safe automation systems for the plants.

ETOGAS, Germany - By the year 2050 – this is the country’s ambitious goal – 80 % of Germany’s energy supply should be provided by renewable energy sources. However, one prerequisite for this is the availability of sufficient storage capacity for energy from renewable sources, according to Michael Doll, head of electrical engineering at ETOGAS. He says, “Everybody knows the problem, which is that, at certain times, more energy is produced from wind and the sun than is consumed. Our plants can chemically store this excess energy.” The first step in this process involves water being split into hydrogen and oxygen via electrolysis. In the second step, the hydrogen is then converted with carbon dioxide (CO2) to methane (CH4), which is directly fed into the natural gas network and can also be stored in the existing infrastructure for natural gas storage.

(Photo: kati ebner)

From idea to application

The general feasibility of the process was successfully proven on a kilowatt scale in 2009 at a demonstration plant at the Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW, Center for Solar Energy and Hydrogen Research Baden-Württemberg), ETOGAS’s research and development partner. Already back in October 2012, ZSW inaugurated a research plant with a connected electrical load of 250 kW.

This plant consists of an alkaline pressure electrolyzer, a methanation unit, and a process control system for control and regulation, which is already state of the art for future large-scale industrial plants. “Of course electrolysis is not a new process; however, the challenges were not to be underestimated,” reports Doll. “We are one of the first companies making this classic method of electrolysis and methanation switchable and thus providing it with a load capacity. After all, this is one of the basic requirements for suitability as an energy storage medium.” The research plant with a capacity of 250 kW can flexibly respond to a changing energy supply from wind power and photovoltaic systems as well as sudden power generation blackouts.

Safe process control

As this is a chemical process, power-to-gas plants are operated and also automated like regular process plants. ETOGAS uses the Simatic PCS 7 process control system, which has proven itself in the process industry. For ETOGAS, the scalability of the system is a particular advantage of PCS 7. Because this plant – like many other power-to-gas projects – started out as a pilot system, the experience gained there can be transferred quickly and smoothly to the large-scale system. “Maybe we could have automated the research plant in a different manner, but having the first plant already equipped with PCS 7 paid off. This made the switch from the pilot to the production system much easier,” emphasizes Doll.

And the step to the production system was seamless. In Werlte in Northern Germany, the world’s largest power-to-gas plant has been developed, constructed, and put into operation. The plant has a connected electrical load capacity of 6 MW and converts excess renewable energy into hydrogen and methane. The plant will produce an average of 3 million m3 of synthetic methane per year. The same automation technology components, based on Simatic PCS 7, were used as in the 250 kW plant. Siemens also supplied the switch cabinets and provided engineering services such as some of the programming and the electrotechnical project management as well as the electrotechnical connection of the approximately 1,000 I/O devices.

Following successful tests of the new renewable energy storage technology, this first industrial-scale plant was successfully put into operation in the fall of 2013. The experience and results obtained in the research operation now benefit the new system. The synthetic methane generated with the help of renewable energy, called e-gas by Audi, is intended for customers of the new A3 g-tron. Using this fuel, drivers can drive almost CO2 neutrally, with a CO2 balance of 20 g/km. The amount of gas from Werlte is sufficient to supply 1,500 A3 g-trons with an annual mileage of 15,000 km each – for a total of 22.5 million km.

The field devices installed in the system deliver reliable measurements of current pressure and temperature. The diagnostic functions of the devices can be accessed and parameterized centrally via the Simatic PDM software tool included in PCS 7 (Photo: Siemens AG)

Insights for the future

Despite the large dimensions of the plant in Werlte, this is still a research project. And that means a two-year research phase will follow the initial operation. The remote access option offered by the Simatic PCS 7 automation system is therefore helpful not only in diagnosing possible errors but also in regard to the optimization of the entire process, as the data from the operation are analyzed by ZSW to optimize the plant still further.

There is no lack of interest in this innovative process. Wind farm operators as well as network operators and the fuel industry are currently looking into alternative possibilities for energy storage. What is crucial here is that the dynamics of the process enable a flexible response to the changing supply of solar and wind energy – which is the reason why ETOGAS and Siemens are continuously developing their solutions for the storage of renewable energy.