Using lithium ion batteries to even out renewable energy production

August 21st, 2012 by Karlsruhe Institute of Technology

Energy storage systems will make renewable energy more practical as fluctuating supplies of electricity from photovoltaics and wind power can be stored until use.

At Karlsruhe Institute of Technology (KIT) in Germany, several pilot plants that include photovoltaic panels, 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 lithium ion batteries can already be applied in the grid today,” said Dr. Andreas Gutsch, coordinator of the Competence E project.

As stationary storage systems, lithium ion batteries can store solar or wind power until it is retrieved by the grid.

“When applied correctly, batteries can balance higher load and production peaks and, hence, make sense from an economic point of view.”

The Competence E project is developing several pilot systems consisting of photovoltaic panels 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,” Dr Gutsch said.

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 photovoltaic system.

The first stage of the project will be able to cover electricity consumption of a medium-sized company throughout the year.

The research 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.

The stationary storage system can be applied as an interim storage system for peak load balancing.

During times of low electricity consumption, electricity produced by solar and wind energy will be fed into the battery.

At times of peak electricity demand, the energy from the photovoltaic system, the wind generator, and the battery will be fed into the grid.

Apart from load management, night discharge is of significant economic importance, because consumption of photovoltaic 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,” Dr Gutsch said.

“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 the economic efficiency of the complete system.”

“Such a system can be controlled 24 hours a day and 365 days a year with detailed battery know-how. Only then will economically efficient and safe operation be guaranteed for decades,” Dr Gutsch said.

After testing, 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 now, 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 photovoltaic 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 photovoltaic-based electricity consumption by the private customer.


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