A Danish company wants to convert coal power plants into large-scale energy storage facilities

Danish company Aalborg CSP is proposing a revolution in how old coal-fired power plants in Europe are decommissioned. Instead of costly demolition, the company is developing a technology that converts coal units into large-scale thermal energy storage systems integrated with wind and solar farms. It’s an idea that could transform the phase-out of coal—not by “cutting the cables,” but by giving existing infrastructure a second life.

A second life for coal units instead of demolition

According to Aalborg CSP, more than 250 coal-fired power plants in Europe are scheduled to be shut down by 2030. The standard scenario involves expensive, multi-year decommissioning processes followed by building new renewable energy and storage installations from scratch. The Danes propose an alternative: make use of what already exists—turbines, generators, grid connections, transformers, buildings—and convert the coal unit into part of the green energy infrastructure.

The company emphasizes that such a conversion not only reduces dismantling costs but also helps maintain jobs in mining and energy regions. Instead of a “closed mine and a dead power plant,” local communities could benefit from a modern energy hub supporting the growing share of renewables in the national energy mix.

Power-to-Salt: the Carnot battery made from molten salt

At the heart of Aalborg CSP’s solution is Power-to-Salt technology, described as a “Carnot battery.” The concept is simple:

• when there is an excess of cheap wind or solar energy, electricity is converted into heat, which is stored in molten salt in large, well-insulated tanks,
• when demand rises, the thermal energy is converted back into electricity using the existing steam turbine.

In practice, this means replacing the coal boiler with a steam system powered by salt heated to around 565°C. The system uses two large molten-salt tanks—“hot” and “cold”—between which the medium circulates. Thanks to proper insulation, the storage system can hold energy for long periods, regardless of weather conditions.

The key is that much of the coal unit’s infrastructure remains in use: turbines, generators, some heat exchangers, electrical installations, and grid connections. This reduces capital expenditure and shortens deployment time compared to building an entirely new energy storage facility.

Benefits for the climate, the power system, and local communities

As Jens Taggart Pelle, Vice President of Technical Sales at Aalborg CSP, highlights, converting coal plants into energy storage facilities brings several key benefits:

• Environmental – CO₂ reduction by replacing coal combustion with a storage solution integrated with renewables.
• System-related – improved grid stability with growing shares of intermittent sources such as wind and solar.
• Economic – new revenue streams from balancing services and selling stored energy, while avoiding the cost of plant decommissioning.
• Social – preserving jobs and retraining part of the workforce to operate modern energy storage infrastructure.

Pelle notes that plant owners can shift from being coal-based power producers to operators of flexibility services for the power system—without losing their key technical assets.

Pilot project in Bulgaria: from coal to a stabilizer for renewables

Aalborg CSP is testing its concept in cooperation with AES Bulgaria, the local branch of U.S. company AES Corp. The aim of the study is to determine how a modern coal-fired power plant built in 2010 could be converted into a thermal energy storage system using Power-to-Salt technology.

The project is intended to support better integration of renewables into Bulgaria’s energy system—including greater use of wind and solar—while maintaining high grid stability. Ivan Tzankov, CEO of AES Bulgaria, emphasizes that this is an opportunity to repurpose existing infrastructure as a “clean” energy asset for decades to come instead of abandoning it at high cost.

The future of coal plants: burden or resource?

Aalborg CSP’s concept fits into the broader debate on what role old coal plants should play in the energy transition. Instead of treating them solely as regulatory and financial liabilities, the Danes propose turning them into key components of green energy infrastructure—large-scale storage facilities ready to support the increasing number of renewable sources.

If Power-to-Salt technology proves its cost-effectiveness and reliability in pilot projects, European energy systems may gain a powerful tool for balancing renewables. For many regions that have relied on mining and coal power for decades, this could offer a smoother, more predictable transition to a zero-emission future—while preserving infrastructure, skills, and jobs.