Converting old coal-fired power plants into storage facilities

29.10.2025

Source: E & M powernews

The Danish solar thermal company Aalborg CSP wants to convert decommissioned coal-fired power plants into thermal energy storage systems for electricity from wind and sun.

Numerous coal-fired power plants in Europe are on the brink of closure. The Danish company Aalborg CSP A/S does not see this as a legacy, but as potential: instead of demolishing the plants, they are to store electricity from renewable sources in future. CSP stands for concentrated solar power. The company is developing a concept for this that largely preserves the existing power plant infrastructure and converts it into thermal storage facilities.

According to Aalborg CSP, the need for storage capacity is growing rapidly, as grid stability is becoming more dependent on flexible storage as electricity generation from wind and solar power increases. "We see the conversion of coal-fired power plants into energy storage as an economical and climate-friendly solution," says Jens Taggart Pelle, Vice President of Technical Sales at Aalborg CSP. Owners benefit from lower decommissioning costs, new sources of income and an improved public image.

Salt storage instead of coal

According to the company, most of the components of a coal-fired power plant can still be used. Steam turbines, generators and heat exchangers are retained, while the previously coal-fired boiler is replaced by a new system. This is based on so-called power-to-salt technology: surplus electricity from wind and solar plants is converted into heat and stored in molten salt. When required, the system generates electricity again via a steam generator system.

The technology uses a Carnot battery that heats the salt to around 565 degrees Celsius. The salt is stored in two tanks - one hot and one cold. When energy is required, the hot salt releases the stored heat via heat exchangers and drives the turbines of the existing power plant. In this way, the converted power plant can continue to generate electricity and heat without burning fossil fuels.

Contribution to grid stability

Aalborg CSP also sees this as a contribution to security of supply. "Our storage technology can stabilize the grid by absorbing energy from renewable sources and releasing it at times of high demand," says Pelle. At the same time, jobs could be preserved as the operation and maintenance of the converted systems would offer new employment opportunities.

According to the company, there are more than 250 coal-fired power plants in Europe alone that are due to be decommissioned in the coming years. For their owners, the question arises as to whether investments in new storage projects are worthwhile. Aalborg CSP argues that retrofitting existing plants is more cost-effective than building new storage facilities. The existing infrastructure could continue to be used for many years.

Economic opportunities

In addition to the ecological benefits, the company points to economic opportunities. By using cheap electricity from renewable energies, operators could reduce operating costs and generate additional revenue through system services. Arbitrage transactions on the electricity market are also possible - i.e. the sale of stored energy at times of high prices.

"Our calculations show that the conversion of coal-fired power plants is the most cost-effective solution," explains Pelle. "In this way, owners can not only avoid dismantling costs, but also play an active role in the energy transition." The concept is scalable and can be adapted depending on the size of the site and grid requirements.

Aalborg CSP has been developing systems for solar thermal energy and industrial heat storage for years. With the approach of converting coal-fired power plants into thermal storage, the company now wants to take its technology to a larger system level - as a link between renewable power generation, grid stability and heat utilization.

Author: Susanne Harmsen