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Supplying energy safely requires
powerful energy buffers
But it makes no difference how lightweight a vehicle can be
made through structural measures or how much CO 2 can be
eliminated: in the end, the most important consideration
when it comes to tomorrow‘s mobile and stationary energy
supply is still energy storage. The reason for this is that
renew able energies generate extremely uneven loads on supply
networks, which are currently compensated by regulatable
power plants and, to a lesser extent, pumped-storage
power plants, which have limited potential.
Accumulators and supercondensers are the only highly
effective means for storing electrical power. Prof. Martin
Winter of the Institute for Physical Chemistry at the Uni versity
of Münster believes that lithium-ion technology will
play a key role in this technology. As he sees it, there are
four reasons for this: high cell voltage, high energy and power
densities, low self-discharge rates, and the ability to exploit
the battery‘s entire capacity without damaging it. “The
lithium-ion battery is an evolutionary technology, because
so many different materials can be used to produce it. It’s
ideal for quickly buffering power spikes in a matter of
hours,” said Winter. Suitable for small- to medium-sized decentralized
energy buffers, lithium-ion technology will probably
also play a role in future vehicle-to-grid designs, for
which the batteries of electric vehicles would serve as temporary
buffers for power spikes. This would take advantage of
the fact that many vehicles are not moved for most of the day.
But there are also clear ideas for stationary applications:
the LESSY (lithium electricity storage system) prototype,
made up of about 5,000 individual lithium ceramic cells, will
be developed this year at Evonik‘s coal-fired power plant in
Völklingen, Saarland. With an input and output of 1 MW and
a storage capacity of about 700 kWh, LESSY is slated to provide
primary regulation. Evonik’s partners on the project include
its own subsidiary Li-Tec Battery GmbH, a joint venture
with Daimler AG, and the University of Münster, under
the direction of Winter, among others. The Federal Ministry
for Education and Research is funding the project under its
LIB 2015 research initiative.
Prof. Martin Winter
of the Institute for
Physical Chemistry at the
University of Münster
Hydrogen as a future primary energy store?
Compared to lithium-ion technology, the sustainable production
of hydrogen is still in its infancy. The volatile gas
would be an attractive source of primary energy because it
contains more energy per weight units than any other chemical
fuel. “Currently, however, 96 percent of hydrogen is
generated from fossil energy sources. Renewable energies
would be preferable so that hydrogen could play a larger
role in sustainable energy concepts,” said Dr. Henrik Junge,
group leader at the Leibniz-Institut für Katalyse e.V.
(LIKAT). To this end, LIKAT is researching photocatalytic
hydrogen production from water and—as buffer—the release
of hydrogen from formic acid.
For the first topic, LIKAT is testing an iridium-based
photosensitizer embedded in an iron complex, and is using
it to reach a turnover number (as a measurement for the
effectiveness of the catalyst) of 3,000. A fuel cell equipped
with this photosensitizer supplied 18 mW of constant power
for 30 minutes in a test setup. The second LIKAT project,
the release of hydrogen from formic acid, is based on a CO2 neutral cycle, and uses a ruthenium catalyst to release the
hydrogen. On the pilot scale, at room temperature, the process
ran for over eleven days and achieved a 99 percent
yield: 0.9 liters of hydrogen per hour. There is still a long
way to go, however, before
the LIKAT projects can be
used on the commercial scale.
Junge compared the current
state of the technology to the
status of nuclear fusion research.
Dr. Henrik Junge
group leader at the Leibniz-Institut
für Katalyse e.V. (LIKAT)
10 elements32 evonik science newsletter