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.
“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.”
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.
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.
