If Germany is to meet its ambitious goals of getting a third of its electricity from renewable energy by 2020 and 80 percent by 2050, it must find a way to store huge quantities of electricity in order to make up for the intermittency of renewable energy.

Siemens says it has just the technology: electrolyzer plants, each the size of a large warehouse, that split water to make hydrogen gas. The hydrogen could be used when the wind isn't blowing to generate electricity in gas-fired power plants, or it could be used to fuel cars.

Producing hydrogen is an inefficient way to store energy—about two-thirds of the power is lost in the processes of making the hydrogen and using the hydrogen to generate electricity. But Siemens says it's the only storage option that can achieve the scale that's going to be needed in Germany.

Unlike conventional industrial electrolyzers, which need a fairly steady supply of power to efficiently split water, Siemens's new design is flexible enough to run on intermittent power from wind turbines. It's based on proton-exchange membrane technology similar to that used in fuel cells for cars, which can operate at widely different power levels. The electrolyzers can also temporarily operate at two to three times their rated power levels, which could be useful for accommodating surges in power on windy days. 

Germany, which has led the world in installing solar capacity, isn't just concerned about climate change. Its leaders think that in the long term, renewable energy will be cheaper than fossil fuels, so it could give the country an economic advantage, says Miranda Schreurs, director of the Environmental Policy Research Center at the Freie Universität Berlin. Germany will serve as a test case to show whether industrialized countries can compete while relying on renewables.

Another reason Germany is turning to renewable energy is to meet its goal of reducing emissions of greenhouse gases by 40 percent by 2020, relative to 1990 levels, and by 80 percent by 2050. Some other countries have similarly ambitious carbon dioxide reduction goals, but Germany stands out because it's a large economy that depends on cheap electricity to make manufactured goods. It has decided to not to use nuclear power as a source of steady, carbon-free electricity. And it can't rely heavily on natural gas, which emits about half as much carbon dioxide as coal. Natural gas is more expensive in Europe than in the United States, and it comes from countries such as Russia that aren't always reliable suppliers.