BERLIN -- Germany has taken the lead in the international effort to develop the so-called hydrogen economy, focusing on ways to convert electricity from renewable energy sources, such as wind power -- which is sometimes so plentiful it is dumped -- into hydrogen that can be stored and used for a variety of purposes, beginning with fuel-cell-powered cars and buses.
The theory has been that excess electricity from wind power could be used in electrolysis to split water into its two constituent parts: oxygen and hydrogen, a flammable gas that can later generate more electricity. Linde Engineering, together with several oil and gas companies, is teaming up with leading automobile manufacturers, including Daimler AG and BMW, to install a network of public fueling stations to pump hydrogen into fuel-cell vehicles. The so-called Clean Energy Partnership (CEP) is a federally supported program that will enable motorists to reach any destination in Germany without refueling.
Full coverage would require around 1,000 stations, and by 2016, the program hopes to meet its target of 50 stations deployed among five regions. A second program, H2 Mobility, includes a smaller number of industrial firms and aims to have 400 stations in place by 2023.
"The refueling stations will simultaneously be important test beds of innovative technologies for the safe and fast refueling of hydrogen," said Oliver Ehret, a program manager at the National Organization Hydrogen and Fuel Cell Technology, the authority charged with coordinating the fuel station rollout.
Studies indicate the need for a combination of decentralized and centralized hydrogen production. Depending on the usage, you may want smaller on-site electrolyzers in urban areas or more centralized power-to-gas facilities such as Energiepark in Mainz to service less-traveled routes in refueling stations sited on the German Autobahn, for example.
The point, Ehret continued, is to have the car manufacturers and the infrastructure companies work together with the hydrogen producers so that a scaled-up rollout can begin. A hydrogen filling station can cost €1 million to €1.5 million ($1.7 million) to install.
With 90 hydrogen fueling stations installed worldwide, the company is the leader in this sector. Linde manages in Vienna what it says is the world's first small-series production for hydrogen fueling stations. Together with Total, which manages most of the refueling stations in Germany, it could possibly begin to fulfill the vision.
Fuel-cell cars are rolling into the showrooms. Toyota Motor Corp. and Hyundai Motor Co. have launched their models. Daimler, Volkswagen Group, Audi AG and BMW have prototypes. More models are expected by 2017, by which time more power-to-gas facilities are expected to be available.
"The big idea of hydrogen is to use it to integrate renewables, but then use them in different sectors," Ehret explained. "It's really about shifting the entire energy world."
Finding multiple uses
Other sectors where the hydrogen economy is taking shape involve bigger, commercial-scale electrolyzers that can either create hydrogen for storage or feed it directly into Germany's natural gas pipeline system. The process gives off zero carbon emissions, making it possible to integrate renewables into disparate fields of chemicals production and heat and power generation.
Batteries aren't always well-suited for power storage. First, they're still expensive. Secondly, they're mainly geared to storing electricity for just a few days. And they don't offer a viable means of storing surplus power from the summer to winter.
In the reconversion of hydrogen back to power, only 30 to 45 percent of the original energy is retained. But in other processes, like its capacity to provide a prompt demand response to electrical grids, and in heating and transport, hydrogen energy technologies are beginning to demonstrate a business case.
The strength of the power-to-gas concept is the way that it addresses multiple challenges using existing infrastructure in the form of the gas distribution system and conventional gas-fired electricity plants, while also providing hydrogen for direct reconversion into electricity, said Thomas J. Schmidt, head of the Electrochemistry Laboratory at the Paul Scherrer Institute, which operates under the domain of the Swiss Federal Institutes of Technology.
Yet of all the applications, mobility presents perhaps the most immediate and exciting one in its scale-up potential.
"Right now, we're in a very lucky situation," said Schmidt, citing the emergence of hydrogen fuel-cell vehicles as an enabler of electrolysis technologies.
For years, hydrogen advocates have found themselves stuck in a chicken-egg situation: Without a sufficient network of refueling stations and requisite amounts of green hydrogen, car manufacturers held back on a full-throttle commitment.
"It's changed from this," Schmidt added, "and now we have parallel growth, both in terms of fuel-cell cars and the deployment of electrolysis units for hydrogen production."
Big electrolyzers enter the market
In Germany, there are nearly two dozen renewable hydrogen production facilities experimenting with improved electrolyzer technology. These power-to-gas projects are typically led by utilities that find themselves in regions that have plenty of wind-generating capacity. The biggest and most important include a plant launched by the automaker Audi together with ETOGAS and EWE in Werlte, west of Bremen.
Started in late 2013, it draws carbon dioxide from the exhaust stream of a biogas facility and then mixes it with hydrogen produced on site in a methanization process that then feeds the resulting synthetic fuel into the local gas grid for distribution to filling stations that sell compressed natural gas to car owners. In this way, Audi is able to power its A3 g-tron vehicles. The 6-megawatt plant can boot up within five minutes and recently qualified to enter the secondary balancing power market to be needed when electricity from wind power is in surplus.
Utility giant E.ON has a power-to-gas demonstration project in operation in the village of Falkenhagen, east of Berlin. Here, the hydrogen is fed into the gas grid and then sold as an additive product to natural gas customers. Partners of E.ON are the electrolyzer manufacturer Hydrogenics Corp. and Swissgas AG.
Both of these projects obtain hydrogen from conventional alkaline electrolyzers, a technology that has been on the scene for the better part of a century. By contrast, newer proton exchange membrane (PEM) electrolyzers can convert excess renewable electricity into hydrogen within milliseconds -- something the Werlte plant is unable to do.
PEM electrolyzers can be run hard or slow, thus allowing the operator to take advantage of variations in electricity prices. They produce more hydrogen when prices are cheap and run at optimal efficiency, or not at all, when electricity is expensive.
Industrial-scale PEM electrolyzers are now online at two sites in Germany: in Hamburg, where a 1-MW PEM electrolyzer converts excess electricity from renewable energy to hydrogen and is operated by E.ON, and in Mainz through a partnership of Siemens AG and the gas and engineering company Linde, together with the local municipal utility Stadtwerke Mainz AG.
The Hamburg plant has the largest single PEM electrolyzer stack. "Large stacks reduce system costs, though several small stacks have the advantage of being more modular," explained Schmidt. In the long run, bigger single stacks will be needed, but at this point, there's quite a lot of variation on how best to get there, he added.
A big 'bet on the future'
In Mainz, four 2-MW windmills are coupled to three PEM electrolyzers, each with a peak power of 2 MW. That makes it the largest PEM electrolyzer operating in the world, according to the project partners.
"For larger scales, multiple stacks must be used," said Erik Wolf, a product expert at Siemens' electrolysis division. "To change the design project by project is not yet cost-efficient."
The design goal at this point is to operate at a maximum 65 percent efficiency, with an 80 percent efficiency output also possible, should the machine be operated in such a way as to reduce costs. As in other projects, hydrogen will be blended into the natural gas distribution system.
There are limits to pumping hydrogen into the German natural gas pipeline system. It is currently set at 2 percent, but there is so much capacity in the German gas network that there is ample room for adding hydrogen, explained Simon Bourne, the chief technology officer at ITM Power, a British company specializing in the manufacture of PEM electrolyzers.
Another option is to burn the resulting gas and pump the waste heat into citywide district heating systems that heat homes and buildings. ITM Power did just that recently with a PEM electrolyzer it installed for the utility RWE AG in Ibbenbüren. RWE tested this and stated an electrolyzer efficiency of 86 percent, the highest recorded so far for a commercial electrolyzer system.
Using the hydrogen directly for fuel-cell cars and buses requires a second process that raises its pressure. For Stadtwerke Mainz, which may want to operate fuel cell buses in the future, this would require a refueling station at their bus depot or an extra tour to the Energiepark. Linde estimates the plant will produce enough hydrogen to supply 2,000 fuel-cell cars, something it would likely do by delivering hydrogen via trailer to gas stations.
"In the end, electrolysis is the most expensive tool that we have today," said Christoph Stiller, head of energy storage for Linde. But he is quick to add: "This is a bet on the future, on the mobility option getting stronger. The more electrolyzers we install, the cheaper it will get."
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