German Coal conversion to Heat Pump Energy Storage

Germany, like many other countries, has coal plants used to produce power all over the country. However, due to new investments in renewables and tackling climate change, it is now being investigated whether these coal plants could be used as energy storage assets instead. The German aerospace centre has been investigating this possibility. 

The idea involves using a molten salt storage tank in place of the old coal boiler and excess power produced by renewables will be used as heat for the tank. It is thought that the coal plants still being in use, could save many jobs which would otherwise be lost by their closure.  Another advantage of these storage plants would be their capacity of tens of gigawatts of extra power available to be used to power the country. The German grid may well be powered more by renewables than anything else if these changes take place. 

A pilot project is soon to take place and the results will be crucial to the development of more similar projects. Just one project could prove the success of the use of coal plants as renewable storage and it is hoped it could up and running within three years. The technology used is called a Carnot battery.  

A Carnot battery is used to turn electricity into heat. It is seen as environmentally friendly and is fairly inexpensive. Carnot batteries are a relatively new technology in renewables. The heat is stored in molten salt or water and can be turned back into electricity when needed, making these the ideal solution in renewable storage. Carnot batteries have been researched by DLR since 2014, the main challenge being to make the salt storage and batteries fit within the coal plant. 

Many utility companies in Germany have been hoping for longer use of coal plants, however they have now been given a cut off date with many plants being closed by 2023 and even more planned by 2030. This seems like the sensible option – to reuse the infrastructure and save many jobs in the industry. 

Whilst there is the challenge of fitting the technology into the existing infrastructure, it is not thought that cost will be huge. Energy is converted into heat at a temperature between 90°C and 500°C using a high-temperature heat pump, these are called Carnot batteries and they offer really good value as there will be no need for much building works due to using the old coal plants to house the new boilers and batteries. Grid connections are already available making the projects cheaper and easier to reuse.

While Germany hope to use the Carnot batteries, they also hope to use them in harmony with lithium ion batteries. This means there is backup power available, renewables could be used from the grid and when this power becomes low, for example in winter months, lithium ion batteries could provide the extra power needed. Some of the coal plants could remain, with coal boilers as well as the new salt boilers for emergency backup if necessary. 

Johnathan Walters said: 

“You’re going to lose the lignite jobs,” he said, but “you’re going to save the power plant jobs and you’re going to save some of the physical assets that would otherwise be written off.”