Bulgarian coal plant mulls replacing boiler with molten salt battery

The operator of the AES Maritsa iztok 1 coal plant in Bulgaria is interested in replacing one of its boilers with a molten salt reactor. It would accumulate excess renewable energy from the power grid as heat and produce steam to drive the existing turbine.

With the surge in solar and wind power capacity throughout the world, the grid needs to match it with balancing and flexibility to handle the intermittency of the two sources. Their output varies with weather conditions, so the amount of electricity is often much higher or lower than demand.

Batteries are all the rage now, with investors racing to bridge the gaps between intraday peak production and peak consumption. Southeastern Europe is catching up with the trend, especially in Bulgaria, Romania and Turkey.

A molten salt battery could turn out to be a lifeline for AES Maritsa East 1

It opens up space for some other solutions in the emerging energy storage market which are nearing maturity. United States-based AES Corp.’s subsidiary in Bulgaria is examining one such overlooked opportunity. The molten salt reactor technology could revive the prospects of its coal power plant in Galabovo in Stara Zagora province.

The operator of the AES Maritsa iztok 1 (AES Maritsa East 1) facility is planning to transform one of the units into a so-called Carnot battery, Capital.bg reported. Such systems turn electricity into thermal energy and store it, to convert it back to electricity.

AES plans to maintain generator’s capacity

The company’s solution of choice is a molten salt reactor, which would replace the boiler. AES plans to power it with surplus renewable energy and produce steam for the existing 345 MW turbine. Importantly, among its other assets is the Saint Nikola wind power plant of 156 MW, the largest in Bulgaria.

The battery would hold enough heat to drive the unit at maximum power for five hours, translating to 1.73 GWh.

Coal plants can technically work nonstop, but the market has all but overrun most such facilities in Europe. Now they increasingly operate only when prices are high, covering peaks. It could make the business case for molten salt reactors and preserve jobs.

Molten salt is used in concentrated solar power (CSP) plants. They mostly use electrolytes such as alkali metal chlorides – sodium chloride, potassium chloride or lithium chloride – or nitrates: for instance, sodium nitrate or potassium nitrate.

Need for energy storage strengthening with rise in intraday price spreads

Market prices were negative on 2.8% of the days of last year, while they were lower than EUR 5 per MWh for 8.8% of the time. It compares to 1.9% and 5.5% in 2025, respectively, the article adds. The spread between the maximum and minimum prices is increasing. On 53% of days in the first half of this year, the difference was between EUR 100 per MWh and EUR 200 per MWh. The share of spreads above EUR 200 per MWh was 30%.

Such high amplitudes indicate both oversupply and shortages within the same day, amid the strong growth in variable renewables capacity.