Enel-owned power company Endesa has taken the first steps to add battery storage to one of the largest thermal generation plants in Spain. The innovation will help make the plant more efficient and flexible, reducing emissions and the need for maintenance in order to prolong the plant’s useful life, the company says.

If it goes ahead, the project will be unique in the world of energy storage. And it might just remain an outlier, according to analysts, who think it’s unlikely that it represents the beginning of a trend for coal-plus-batteries.

In official documents submitted to the Ministry of Energy at the end of December last year, Endesa stated that the energy storage facility would help stabilize the grid and ensure the quality and dependability of energy supply. 

The innovation is necessary, the company claims, as the plant needs to respond to increasing quantities of intermittent renewable energy sources on the grid. These are stresses the plant was not originally built to withstand, which means more maintenance and inspections costs, greater coal consumption and unnecessary emissions. 

Sited in Almería, in the south of the Iberian Peninsula, the 1,158-megawatt Carboneras plant makes a big contribution to Spain’s electricity mix. The country currently gets 19.9 percent of its electricity from coal. 

It’s also one of the country’s biggest single polluters. Endesa hopes a €240 million (USD $259 million) cash injection to update the plant will reduce sulfur dioxide and nitrogen oxide emissions by 60 percent and 80 percent, respectively.

The amount of money going toward its fledgling storage project, which is still in the early planning phase, is not clear. Requests to the company to provide even basic information on the budget, scheduling, scale, and pretty much anything else elicited a “no comment” from Enel’s media department.

All that is known at this stage is that the proposed energy storage system would utilize lithium-ion batteries and would store 30 minutes’ worth of the plant’s output. “The 30 minutes figure would probably indicate that the storage is going to be designed for primary frequency response,” commented GTM Research analyst Daniel Finn-Foley.

There could be a number of advantages to providing a coal plant with storage, although Finn-Foley questioned the long-term future of this combination.

Along with providing frequency response, storage could make the plant more efficient by allowing it to run closer to its optimal capacity. Any excess power generated could then be stored until needed by the grid. 

Greater efficiency could mean lower emissions. However, any calculation of efficiency gains needs to factor in the round-trip inefficiencies of the storage system. 

Although coal-plus-storage is as yet untried elsewhere in the world, large-scale storage is already being used with other fossil generation. Newly installed natural gas peaker plants have been paired with 10-megawatt batteries in California to respond to specific conditions in the aftermath of the Aliso Canyon energy crisis. Manufacturer GE hopes that the combination will find other markets, too, but these opportunities have yet to emerge.

In the case of coal-plus-storage, the opportunities may be thin. Coal is being curtailed worldwide by legislation and market forces as both natural gas and renewables continue to drop in price. It’s increasingly seen as a sunset industry, so unless the current U.S. president makes good on his vow to revive the coal industry, it looks likely storage will be more usefully -- and profitably -- deployed with renewables.

Indeed, the Carboneras plant itself is destined to be slowly scrapped, as Endesa publicly plans to go 100 percent renewable by 2050. The company already uses large storage-plus-renewables on the isolated island grids in the Canaries. And parent company Enel -- which has a whopping 36 gigawatts of installed renewables worldwide -- recently acquired U.S. energy storage specialist Demand Energy.

The Carboneras plan for coal is likely a one-off, designed to squeeze a few extra years out of an expensive asset. The reluctance to go into any details about the project seems to indicate that Enel has no additional plans.