Article published on
http://www.sciencedaily.com , August 9, 2012
Energy storage systems are one of the key technologies
for the energy turnaround. With their help, the fluctuating supply of
electricity based on photovoltaics and wind power can be stored until the time
of consumption. At Karlsruhe Institute of Technology (KIT), several pilot
plants of solar cells, small wind power plants, lithium-ion batteries, and
power electronics are under construction to demonstrate how load peaks in the
grid can be balanced and what regenerative power supply by an isolated network may
look like in the future.
The Competence E project is presently developing several pilot systems
consisting of photovoltaics and wind power plants coupled to a lithium-ion
battery. Over a development phase of two years, a worldwide battery screening
was made. "Now, we know which lithium-ion cells are suited best for
stationary storage systems," says Gutsch. The first stage of the modular
systems will be constructed on KIT Campus North by the end of 2012. It will
have a capacity of 50 kW."High-performance batteries on the basis of lithium
ions can already be applied reasonably in the grid today," says Dr.
Andreas Gutsch, coordinator of the Competence E project. As stationary storage
systems, they can store solar or wind power until it is retrieved by the grid.
"When applied correctly, batteries can also balance higher load and
production peaks and, hence, make sense from an economic point of view."
A newly developed, gear-free wind generator that is
particularly suited for weak wind regions will complement electricity
production by the photovoltaics system in the winter months in particular. The
first stage will be able to cover electricity consumption of a medium-sized
company throughout the year. In the long term, the know-how obtained will be
used to develop smaller storage systems for private households as well as
larger systems for industry.
Apart from the battery, the key component of the
stationary energy storage system is an adapted power electronics unit for
charging and discharging the battery within two hours only. Hence, the stationary
storage system can be applied as an interim storage system for peak load
balancing. During times of weak loads, solar energy and wind electricity are
fed into the battery. At times of peak load, the energy from the photovoltaics
system, wind generator, and battery is fed into the grid. Apart from load
management, night discharge is of significant economic importance, because
consumption of photovoltaics energy by other electric devices of the user can
be increased considerably. The battery is charged in the afternoon and
discharged during darkness until the next morning.
"Controlling the interaction of solar cells, wind
generator, storage systems, and the grid is the central challenge," Gutsch
explains. System control always has to reliably and precisely interfere with
the multitude of operation states. Only this will ensure a good service life
and performance of the lithium-ion batteries in the long term and, hence,
economic efficiency of the complete system. "Such a system can be
controlled 24 h a day and 365 days a year with detailed battery know-how. Only
then will economically efficient and safe operation be guaranteed for
decades," emphasizes Gutsch. After first functional tests, concrete
application systems of variable power will be produced in cooperation with
industry.
In spite of the high costs of lithium-ion batteries,
this technology may be worthwhile today already, in particular in regions that
do not have any stable grids. Smaller and larger islands, for example, are
often supplied with electricity by diesel generators. In Africa and India,
large areas are not supplied with electricity at all. A photovoltaics system
with a coupled lithium-ion battery can be applied profitably, if appropriate
system design and load profile are chosen. With decreasing costs of system
components, we will achieve "battery parity" in Germany, in analogy
to the "grid parity" already reached for photovoltaics-based
electricity consumption by the private customer.
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