Carnot batteries can store and release electricity as heat using different materials, such as water, molten salt, or rocks.
Coal power plant stock photo. Small Steam Generators
A team of researchers from the Technical University of Denmark has developed a novel idea to transform coal power plants into renewable energy sources using Carnot batteries.
Carnot batteries can store and release electricity as heat using different materials, such as water, molten salt, or rocks. They can also work with various methods, such as liquid air, thermal cycles, or sorption techniques. Carnot batteries can help balance the grid by storing excess power from solar or wind farms and supplying it when needed.
The researchers said that old coal power plants are perfect places to install Carnot batteries, as they can reuse some of the existing infrastructure, such as steam turbines, boilers, and heat exchangers. They also said that Carnot batteries can provide grid stability using conventional generators instead of inverters.
The researchers focused on a specific type of Carnot battery that uses a large tank of rocks as the storage medium and air as the heat carrier. They applied their concept to a 300-megawatt (MW) coal power plant in Chile that produces steam at 565 degrees Celsius, °C (1,049 degrees Fahrenheit), and 160 bars of pressure.
Technical University of Denmark, Journal of Energy Storage
They modeled a rock bed storage system with a capacity of 1.37 GWh (gigawatt-hour) and a temperature of 730°C. They placed the heaters, valves, and pipes on top of the tank to make it easier to install and maintain. They also minimized the heat losses and pressure drops in the system.
They designed the system to charge during the day using solar power from photovoltaic plants and to discharge during the night or when solar power is unavailable. They connected the electric heater to the rock bed tank and the steam generator to the coal plant’s turbine and condenser.
They analyzed the system’s performance and found that it could produce about 443 GWh of net power per year for 4 hours of storage, 797 GWh for 8 hours of storage, and 1,150 GWh for 12 hours of storage. They also found that the system was more efficient and cheaper for larger storage capacities. They said the system was competitive with conventional power plants and other alternatives that use molten salt as the storage medium.
They published their results in the Journal of Energy Storage titled “Retrofit of a coal-fired power plant with a rock bed thermal energy storage.”
They suggested that further studies could optimize the system and identify the best operation and sizing for the lowest cost and highest revenue. They said that their idea could help coal power plants transition to renewable energy production and reduce greenhouse gas emissions.
The same research group had also conducted another study earlier this year, exploring the economic viability of Carnot batteries in a 100 percent renewable energy scenario for Denmark.
They reported that Carnot batteries would be competitive if they could achieve a levelized storage cost (LCOS) of less than €66.2/MWh, assuming that gas prices remain low. They said this finding encouraged the future development and deployment of Carnot batteries.
Power production accounts for about one-fifth of the global final energy consumption and over one-third of all energy-related CO2 emissions. Low-cost, large-scale thermal energy storages are considered as solutions for the decarbonization of fossil-fired power plants by their conversion into power-to-heat-to-power systems, so-called thermal storage power plants. This paper investigates the retrofit of a Chilean coal-fired power plant with an innovative solid media storage from a techno-economic perspective. Selecting a storage capacity of 5.27 GWhth, corresponding to 8 h of discharge, and increasing the inlet steam generator temperature from 590 to 650 °C lead to the highest annual round-trip efficiency of 34.9% and to up to 3.4% lower levelized cost of electricity. Minimum levelized cost of electricity as low as 88.1 €/MWh is attained and considered as close to competitiveness with well-established molten salt storage systems. A sensitivity analysis shows that assuming even five times lower storage costs, initially the strongest driver of capital expenditure, only meant 4% lower levelized costs of electricity on average. On the other hand, the design of electricity purchase for charging, for example with green power purchase agreements, turns out to be the key lever to a successful implementation.
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Biomass Steam Boiler Rizwan Choudhury Rizwan is a writer and journalist with a background in Mass Communication Journalism, Public Administration, and Political Science. He has covered subjects, spanning from technology and culture to business and automotive industries. He has written for publication platforms such as Mashable, Pinkvilla, Economic Times Auto, and PTI. In his free time, he enjoys sketching, reading, and exploring music, movies, and comics.