The Hydrogen Economy

MIT Technology Review, March 29, 2012

Edited by Andy Ross

Germany must find a way to store huge quantities of energy generated from intermittent renewable sources.

Siemens offers big electrolyzer plants that split water to make hydrogen gas. Producing hydrogen is an inefficient way to generate electricity, since about two-thirds of the energy is lost along the way, but it can achieve the scale needed in Germany.

The Siemens electrolyzers are flexible enough to run on intermittent power from wind turbines. Based on proton-exchange membrane technology similar to that used in fuel cells for cars, the electrolyzers can also temporarily operate at well above their rated power levels, which could be useful for accommodating surges in power on windy days.

German leaders think that in the long term, renewable energy will be cheaper than fossil fuels, so it could give the country an economic advantage. Germany will serve as a test case for relying on renewables, which will also reduce emissions of greenhouse gases. Germany has decided to not to use nuclear power or to rely heavily on natural gas from countries such as Russia.

Keeping electricity costs low while transitioning toward renewable power will be difficult. Solar power is expensive and wind power is intermittent. Even wind turbines in the best locations generate electricity only a third of the time. High-voltage power lines are needed to get the energy from places that happen to be sunny or windy to places where it is needed. Renewable energy accounts for about 20% of electricity produced in Germany, but 20% of the power produced by wind turbines is thrown away due to a lack of such power lines.

The cheapest way to store electricity is to use it to pump water up a hill, and then let it flow down again to spin a turbine and generator when needed. But this only works where there are hills and dams, and most of Germany is flat. The total amount of pumped-water storage in Germany now is about 150 TJ, which is the energy produced in an hour on a sunny and windy day.

Germany has the potential to store a vast amount of hydrogen, because hydrogen can go into existing natural gas pipelines and storage containers. These offer enough capacity for about two weeks of current renewable energy production in Germany. Salt caverns could provide far more storage. Siemens estimates that generating 85% of Germany's electricity from renewable sources will require 100 PJ of storage. That much hydrogen could be stored in a quarter of the space available in underground caverns.

Siemens electrolyzers are about 60% efficient. Then at least 40% of the energy in the hydrogen is lost in generating electricity. So only about a third of the original energy is retained. But all of it would be lost without a storage system. Siemens plans to build systems up to 250 MW by 2018.

AR  This looks good for the long term.