The Hydrogen Economy
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.
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.
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.