Renewables don’t have to be seen as the killers of conventional power plants any more, especially as new thermal storage approaches like carbon thermal batteries that heat solid blocks to 2,400 degrees Celsius emerge alongside existing solutions. The technology called Electric Thermal Energy Storage (ETES) can turn any thermal fossil fuel power stations into a renewable energy storage facility. The process involves combining existing equipment with the new technology—furnaces are replaced by ETES, and the steam cycle and operation process remain as is.
ETES stores large quantities of energy in chambers filled with volcanic rock. Hot air is blown through these chambers, and the stone absorbs the heat. Veronica Diaz Lopez, who handles external communications for Siemens Gamesa, explained the system to POWER as such: “The technology employs an electric heater to charge the storage and a conventional heat recovery steam cycle to discharge the storage. For charging, electricity is converted into hot air and blown through the storage, which is filled with volcanic rocks. In the storage, the heat is transferred from the air to the rocks and stored. During discharging, the flow direction through the storage is reversed and cold air enters the storage from the opposite end. In the storage, the air is heated up by the rocks and leaves the storage as hot air. The hot air is guided through a boiler where the energy is used to produce steam. The steam runs a steam turbine, which in combination with an electric generator, produces electricity. The beauty of the ETES technology is that it is not just a storage technology but a flexibility solution because it can use electricity as well as heat for charging and can provide electricity, heat, and process steam while discharging,” said Lopez. “Further, it can be used to convert fossil-fueled conventional power plants into emission-free GWh storage facilities.”
That’s what’s so special about ETES; sure, there are plenty of storage technologies available for arbitrage or load shifting, but none that can rehabilitate and breathe new life into conventional power assets! It gives a second life to coal power plants that are marked for shutdown and potential demolition.
Hasan Özdem, head of technology management and projects for Siemens Gamesa, who developed the ETES system, told GTM, “It was wind and solar versus coal and gas power plants. What we are saying is no: ETES can give those conventional power plants a space in the energy future by turning them into green storage facilities. As an engineer, it really concerns me because the only problem with conventional power is that they’re polluting the environment; it’s a very, very big negative. But if you take that away, this technology has been working very efficiently for decades. And the upfront costs of these assets are very, very high. Customers are looking for ways to keep them running for another 30 years, and ETES is their [only] choice so far. We have proven that we are the only technology to go beyond a PowerPoint presentation and actually be operational, as we are at Hamburg harbor.”
Siemens Gamesa, a wind turbine manufacturer, began developing the thermal energy storage system a decade ago when the company was still known as Siemens Wind Power. Last year, it finally completed its first (30-megawatt/130-megawatt-hour) demonstration system and plugged it into the grid at Hamburg harbor.
Through this “proof of system” that has been running for over six months already now, the company has shown how effective ETES is; therefore, it could be used very soon to revive coal plants scheduled for closure next year. There are nearly a dozen customers in talks with the firm, ranging from wind farm operators looking to sidestep curtailment rates to recently commissioned coal power plants looking to prolong their life.
ETES is a desirable option because it costs less than other storage alternatives, it doesn’t require certain temperamental chemicals, and it’s simple. Özdem said, “ETES can slot into conventional power assets easily because it mirrors century-old thermal generation technology. Except for the storage chamber, everything else is basically what people have been installing in conventional power plants for decades, if not a century—it’s just a water-steam cycle, steam generators, steam turbines, and pipes.”
It is also possible to build an ETES facility from the ground up at any site with a grid connection.
