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"I Drive to My Local Petrol Station and Fill Up With 50 Litres of Wind..."

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Sometimes you run into metaphors that poetically sum up something that otherwise needs more words: It's the opening sentence on the home page of Enertrag AG, a German avant garde independent power producer that integrates hydrogen production and storage with sustainable energy production and utilization.

Production, storage and reconversion to electricity of very large, volumes of hydrogen gas in natural caverns, aquifers or big tanks under relatively low pressure are seen as key components of a renewable energy economy.

Conceptually similar to compressed-air storage or pumped storage of water in big reservoirs, it is essential to smooth out the irregular ebb and flow of renewable energy sources -- no sunlight at night to produce electricity in solar power plants, and the wind doesn't always blow to run wind turbines -- to assure a steady energy supply for industry and consumers.

Two years ago, Enertrag began to turn that concept into reality. Its executives laid the cornerstone for the world's first -- if small -- 21 million euro ($30.2 million) hybrid power plant that ties together all the elements of sustainable utility-scale energy production for industry and for mobility: cars, trucks, and buses, ships, and even airplanes in a ceremony presided over by a smiling German Chancellor Angela Merkel.

The concept is also designed to ensure electric base load availability, to guarantee forecast stability and to provide power for peak load needs. The plant, located some 70 miles northeast of Berlin in Prenzlau consists of three grid-connected 2 MW wind turbines; a 1 MW installed capacity biogas plant; a 500 kW (120 cubic meter/hour) electrolyzer to make the hydrogen; two 60 cubic meter/hour compressors that squeeze the hydrogen to 30bar (435 psi) for storage in five storage tanks with a combined capacity of 1,350 kg of hydrogen; and two combined heat-and-power plants of 350 kWelectric and 340 kWthermal that can operate on variable gas mixtures -- from a minimum of 30 percent biogas and 70 percent hydrogen up to 100 percent biogas.

The idea is to transport the hydrogen to Berlin to an existing fueling station, part of the Clean Energy Partnership (CEP) in the German capital, to fuel cars and buses. "The integration of renewable energy and energy storage will be of critical importance for a secure and climate-friendly energy supply," said an obviously pleased Merkel at the April 2009 cornerstone ceremony. "With this hybrid power plant, Enertrag has found an innovative solution to the challenge of providing renewable energy appropriate to demand."

Next, a major project integrating renewable energy with hydrogen storage is under way at the new Berlin Brandenburg International Airport. Enertrag is building a 40 turbine wind farm close to the airport with an annual output of 200 GWh; wind power not used to make fueling station hydrogen or electricity will be fed into the public grid. Due to open in 2012, it will include an integrated CO2-neutral filling station built along similar concepts as the Prenzlau plant, built together with France's TOTAL oil company.

In the United States, a much smaller facility built along similar concepts, the University of California Irvine's tri-generation fueling station in Fountain Valley, started operations in August. Here, the raw fuel source is waste, anaerobically digested into biogas at the Orange County Sanitation District.

The station, installed by the university's National Fuel Cell Research Center together with, principally, Air Products and based on Fuel Cell Energy's molten energy fuel cell power plant, produces about 250 kW power used to run the plant; some waste heat that's fed back into the sludge to aid the digestion process; and at least 120 kg of hydrogen/day to fuel 25-50 cars/day.

Energy stored as hydrogen on a truly massive scale is likely to be the key element of Chancellor Merkel's vision for a national shift to renewable energy: In what may be one of the most audacious acts of environmental statesmanship yet, the government announced plans last fall to convert 80 percent of the country's power production to renewables over the next four decades.

Merkel, in presenting the plan Sept. 6, called it "a revolution in the field of energy supply" and efficiency while pledging to keep energy affordable. Her video podcast called it a concept "that will make clear that the age of renewable is achievable faster than many people would have thought." Under her nine-point plan, the share of renewables would climb from the current 15 percent to 50 percent by 2030 and 80 percent by 2050 at a cost of around 800 billion euros ($1.15 trillion) over 40 years -- uncertain perhaps, given Europe's economic and fiscal woes.

Smelling a future business opportunity, industry is heeding Merkel's call: The German electrical equipment giant Siemens is developing end-to-end solutions for generating and storing huge quantities of hydrogen with megawatt-sized PEM pressure electrolyzers in large underground salt caverns. In its research labs in St. Petersburg, Russia , Siemens is also investigating hydrogen-fueled big advanced gas turbines able to handle the higher temperatures encountered when combusting hydrogen, a project described in the fall 2009 issue of the Siemens' semi-annual technology magazine, Pictures of the Future.

Salt cavern hydrogen storage is also intriguing carmakers. Charlie Freese, General Motors' executive director for global fuel cell activities, has said in order to meet the stated goal of cutting carbon dioxide emissions about 80 percent by 2050, fuel cells and hydrogen are critical components:

"The only real high-density energy storage device to store energy on a scale of what some of these new renewable energy production facilities would require is really going to be compressed hydrogen," according to Freese.

He illustrated the issue last year by comparing ways of storing energy in a 2 million cubic meter salt cavern: With compressed air storage, the cavern could hold about 4,000 MWh, enough to run a central European national grid "for some minutes or hours." Filling the same-size cavern with compressed hydrogen could store 600,000 MWh of energy, providing a grid storage buffer "for several days" -- or 3.6 million tank fill equivalents for a Chevrolet Volt. No contest.

At the 2010 World Hydrogen Energy Conference in Essen, Germany, a paper, "Large-Scale Hydrogen Underground Storage for Securing Future Energy Supplies," said if all of Europe were supplied with energy from wind and solar only, the only feasible way to store energy and smooth out fluctuations would be hydrogen: 0.41 cubic kilometers of volume in, typically, salt caverns would store 167 TWh of energy.

Because of differences in energy characteristics, other methods would mean less energy storage capacity but much more space. Pumped hydro, for a long time regarded as the utility storage method of choice, would require 106 km3 of volume -- about twice that of Lake Constance in southern Germany -- to hold only 74 TWh of energy. The main disadvantage is the relatively low round-trip efficiency -- electricity to hydrogen and back to electricity -- of less than 40 percent, but the authors said despite that, hydrogen is the only storage option to permit energy storage in these huge volumes.

Bottom line: Massive production, storage and reconversion of hydrogen to electricity is a key prerequisite for a future carbon dioxide-free sustainable energy economy and the Third Industrial Revolution.

Peter Hoffmann is the editor and publisher of the monthly "Hydrogen & Fuel Cell Letter," www.hfcletter.com. A revised and updated version of his 2001 book, "Tomorrow's Energy - Hydrogen, Fuel Cells and the Prospects for a Cleaner Planet," with a foreword by former Senator Byron Dorgan (D-ND), will be published early next year by MIT Press.

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