However, it is technically feasible, and known under the promising buzzword of "power to gas" (P2G).

The process involves using electrolysis to convert electricity into hydrogen. This gas, or synthetic natural gas produced by further processing, can be transported in the gas grid and stored in gas reservoirs, where it is available for any desired use.

Scientists, plant construction firms and energy providers are already testing this technology intensively in initial pilot plants and research facilities. To learn more about progress this area, take a look at the joint Hydrogen + Fuel Cells + Batteries display at HANNOVER MESSE 2015, where 150 companies from 25 countries are exhibiting storage options for energy from renewable resources.

The technology works, but it is still very expensive. Much remains to be done before it can be used cost-effectively, but this effort may well be worth it for the energy industry. Power to gas could be the key to the use of regenerative power even at times when the sun doesn’t shine and wind doesn’t blow. The industry hopes to be able to use clean power from P2G plants to offset natural fluctuations in wind and solar power.

That makes energy providers the drivers of P2G development. Last summer Eon had already accumulated more than a year of experience with a pilot plant in Falkenhagen, Germany, with an alkaline electrolysis unit as the core element. The plant processes wind power generated by numerous wind turbines in the surrounding area northwest of Berlin. With a power input of 2 MW, it can generate up to 360 cubic meters of hydrogen per hour.

The hydrogen is fed into a nearby gas pipeline belonging to the North German grid operator Ontras. Current regulations allow natural gas to have up to two percent hydrogen content, and experts think that even higher levels are possible.

Eon offers part of the hydrogen generated in Falkenhagen to its gas customers under the name Eon WindGas. Their partner Swissgas in Switzerland also takes a share. Specific use for electricity generation is not planned. According to Eon, the experience from the Falkenhagen plant is valuable for the further development of power to gas technology.

Gaining experience is also the aim of the twelve energy suppliers in the Thüga municipal utility network, which started up a P2G plant in Frankfurt in May. It generates approximately 60 cubic meters of hydrogen per hour from 320 kW of electrical power, for a capital investment of €1.5 million.

The plant uses an electrolysis unit with a proton exchange membrane (PEM), which has the advantage of greater flexibility. It allows hydrogen generation to be quickly ramped up and down or operated in partial-load mode.

The plant in Frankfurt is intended to participate in the load balancing market during its three years of planned operation and supply negative balancing power. This means it will draw electricity from the grid when the load there is very high, in order to reduce the load on the power grid.

The key component of the P2G plant scheduled to start up by 2015 in Energiepark Mainz, near Frankfurt, is a hydrogen electrolysis system developed by Siemens with innovative, fast-response PEM pressure electrolysis units each rated at 2 MW electrical capacity. With a total capacity of 6 MW, it will be one of the largest in Germany. The stakeholders are the Mainz municipal utility company, the Linde industrial group, Siemens and RheinMain University of Applied Sciences in Wiesbaden.

The hydrogen generated from wind power is intended to be fed into the gas grid and used to generate electricity in Kraftwerke Mainz-Wiesbaden’s gas-fired power plant, or transported to industrial users or hydrogen filling stations by tank truck in compressed or liquefied form. Determining the optimal use path is one of the goals of the project, which is initially planned for a two-year run.

The only other P2G plant with a capacity similar to that planned for Mainz is located in Werlte, Germany. There general contractor Etogas built a 6 MW alkaline electrolysis plant that generates up to 1,300 cubic meters of hydrogen an hour. It is operated by Audi, which offers gas from the plant to the purchasers of its natural-gas fueled cars as a clean fuel. Unlike the plants in Falkenhagen, Frankfurt and Mainz, in Werlte the hydrogen is methanized, which means it is converted to synthetic natural gas by further processing.

Although this results in conversion losses, Audi's engines are not compatible with pure hydrogen and their aim with this project is to show that fuel can be produced in a fully regenerative manner. For this reason the CO2 used for methanization comes from a biogas plant operated by the Oldenburg energy provider EWE.

Experts even think that power to gas could reach the filling station level. According to Michael Sterner, a professor of energy science in Regensburg and a pioneer in the technology, cost effectiveness will first be achieved in the mobility sector. Eon also sees possibilities for rapid commercialization, particularly in specific applications such as the mobility sector.

However, until now none of the twenty or so P2G projects in Germany (other plants are also planned or under construction in Freiburg, Karlsruhe, Stuttgart, Schwandorf, Bad Hersfeld, Niederaussem, Herten, Ibbenbüren, Hamburg, Grapzow and Prenzlau) has reached commercial feasibility. Most power to gas projects in Germany to date are demos intended to garner operational experience. The challenge is to identify the first profitable business areas or support commercialization by means of funding programs and a favorable regulatory framework, according to a study by experts at Ludwig Bölkow Systemtechnik in Munich.

Using power to gas technology to convert electricity from renewable resources into a form that can be stored and used as needed to again generate electricity, which is especially attractive for energy supply, is presently not an economically viable option. One reason is that electricity prices are currently so low that even gas power plants cannot be operated at a profit because the fuel is too expensive, and hydrogen from P2G plants costs several times as much as natural gas.

Critics also complain about the high conversion costs with power to gas, which increase with the required number of conversion steps. When electricity is converted to hydrogen, roughly a third of the original energy is lost, and methanization to produce synthetic natural gas takes another bite of a few percentage points. However, this may be necessary because there are technical limits to how much hydrogen can be fed into the gas grid. When the synthetic natural gas is converted back into electricity, as little as a third of the input energy may remain for actual use as energy.

The industry is therefore hoping for further technological progress, more efficient electrolysis units, and benefits on a scale that could significantly lower the currently very high cost of electrolysis.

The regulatory framework also leaves something to be desired. Operators complain that P2G plants in the energy system are treated the same as normal loads and therefore burdened with network charges and the EEC levy when the hydrogen or synthetic natural gas is not used to generate electricity. Operators and proponents of P2G plants argue that exemption from the EEC levy is clearly too narrow because it excludes all other use paths from exempt status.

However, demands for changes to the regulatory framework go even further, advocating that hydrogen and methane from P2G plants should be recognized as fully renewable fuels. The process could then play a significant role in the development of fuels with low climate impact and be pursued as a storage solution for renewable power.

The reasoning is that every new pilot plant could contribute to technological progress – such as the P2G plant with a more compact and more efficient PEM electrolysis unit that Eon wants to put into service this year in Hamburg. Power to gas remains a significant source of hope for the future of the energy industry.

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