Ev charging (Photo: Colourbox)

New invention may ensure more efficient renewable energy storage

Tuesday 07 Jul 20


Kasper Lüthje Jørgensen


Claus Friis Pedersen
A just completed research project has developed a new and much more efficient way of converting energy from wind power and solar cells to—for example—battery storage. With a built-in measuring method, the invention can also be used to monitor batteries, for example in electric cars. 

When energy from wind turbines and solar cells is to be stored in a battery or converted into hydrogen in a catalysis process—which is important in Power-to-X—this takes place by the energy being sent through a converter to ensure the right voltage. Energy loss will always occur in this process, and researchers at DTU have therefore toyed with the idea of transferring energy more directly from the source—for example solar cells—to the battery, thus ensuring greater energy utilization efficiency. 

This has now been achieved through the development of a new method—partial conversion—in which the greatest amount of energy is sent directly to the battery without loss, with only a minor volume passing through the converter. 

“We’ve thus significantly reduced the loss of energy. Where you normally calculate with an energy conversion efficiency rate of around 90%, we’ve improved it to 97%. And the improvement is even greater when—at some point—you need to use the energy from the battery. Here the efficiency is generally around 80 per cent, but our solution has an efficiency of 95 per cent,” says Kasper Lüthje Jørgensen, who has performed the project as a PhD student at DTU Electrical Engineering

Greater efficiency, reduced size, and lower price
The new method not only results in much higher energy storage efficiency, but also in a reduction in the size of the conversion components. 

“We’ve built a prototype of the new invention, which has initially been tested in the two companies participating in the research project. Here, the tests showed the same efficiency improvements that I had calculated theoretically. And the prototype took up little space compared with the components used by the companies so far. The response was so enthusiastic that one company immediately ordered 20 prototypes,” says Kasper Lüthje Jørgensen.

Another important part of the project was to examine the possibility of including the measuring method of electrochemical impedance spectroscopy in the new invention. Also here, the outcome was successful.

“In the long term, the measuring method makes it possible to predict when a battery can no longer deliver the desired performance, and you therefore need to take action. This is interesting in relation to, for example, electric cars—where the owner wants to be aware of faults in the battery— and thus avoid ending up stranded in a place with a car that will no longer drive,” says Associate Professor Zhe Zhang, DTU Electrical Engineering, who has had the overall responsibility for the research. 

Interesting in relation to electric cars
One of the project participating companies is Lithium Balance, which produces battery management systems. The company finds that the invention offers great prospects. 

“We can see a potential in using it in the electric cars of the future, which will have larger, multiple batteries to be able to drive longer. Here, the new invention will be a significant step towards reducing size and price, both for the electric car and the accompanying charging station,” says Claus Friis Pedersen, Director of R&D in Lithium Balance.

“At the same time, the new invention can be used for all voltage types. This is important in relation to the global market, where the electricity grid voltage varies from country to country,” says Claus Friis Pedersen.

Claus Friis Pedersen stresses that it is important to Danish companies to be able to collaborate with DTU and other universities on development tasks such as this project—which can have a major effect on their future products—but which are outside their areas of technological expertise. 

The new invention has been patented, and the next step will now be to continue the project collaboration to mature the method, so that it is ready to be launched on the market and be adapted to applications for a wide variety of different purposes.