| Work Detail |
Danish researchers studied how to integrate solar-powered Carnot batteries into decommissioned coal-fired power plants to produce clean energy. They found that a converted 300 MW coal plant with 1.37 GWh of thermal storage capacity has a net annual energy production potential of up to 1,150 GWh for 12 h of storage at a levelized cost of energy of €88.09 ($95.97)/MWh. Researchers at the Technical University of Denmark have proposed using Carnot batteries to convert coal-fired power plants into renewable energy producers. Carnot batteries are systems that store electricity in the form of heat through storage media, such as water or molten salts, and transform the heat back into electricity when necessary. This category includes liquid air energy storage systems (LAES) and pumped thermal energy storage systems (PTES) based on Brayton or Rankine, as well as Lamm-Honigmann storage, which is a technique based on sorption that can be charged and discharged with both heat and electrical energy, and systems based on resistive heating integrated with power cycles. The scientists explained that decommissioned coal power plants are ideal places to combine electric heaters and thermal storage, as they allow existing equipment such as steam turbines, heat recovery boilers and heat exchangers to be reused. “In addition, conventional generators, rather than inverter-based resources, are capable of retaining a significant amount of inertia for grid frequency stabilization,” they noted. The group investigated, in particular, the conversion of coal-fired power plants through packed bed thermal energy storage and applied their approach to a 300 MW Chilean coal-fired power plant with live steam production at 565ºC and 160 bars. For their modeling, the scientists considered a packed bed facility with a storage capacity of 1.37 GWh and a storage temperature of 730 ºC. The system uses atmospheric air as the heat transfer fluid (HTF) and solid material as the storage medium. Heaters, valves, and inlet and outlet pipes are placed on top of the system to avoid additional excavation and allow bedrock to be installed partially below ground level, making maintenance easier. “The estimated thermal losses for this configuration are 1.94% per day, while the maximum pressure loss over the packed bed, in this work observable during discharge, is calculated at 49 mbar,” the team points out. “The charging time was selected to use the maximum hours of sunlight to represent the use of renewable energy from the photovoltaic (PV) plants, and in this way, the discharge will take place during the night or when light solar is not available.” In the proposed system configuration, the photovoltaic plants feed the electric heater of the storage system connected to the storage tank, which in turn provides heat to the steam generator connected to the steam turbine and condenser of the coal plant. Through their analysis, the scientists found that the retrofitted plant can achieve a net annual energy production of about 443 GWh for a storage capacity of 4 h, 797 GWh for a storage capacity of 8 h and 1,150 GWh for a storage capacity of 12 noon “These values ??are around 3.4% lower when the air temperature at the inlet of the steam generator is set at 590 ºC,” they explained. They also found that the highest annual round trip efficiency of the system was achieved with a storage capacity of 8 h, and that the lowest levelized cost of energy (LCOE) was achieved with the highest storage capacity, at 88.09 euros ($95.97)/MWh. “This value seems competitive both with conventional state-of-the-art plants and with alternatives such as those powered by thermal storage based on molten salts,” they added. Their conclusions were presented in the article “ Retrofit of a coal-fired power plant with a rock bed thermal energy storage,” published in the Journal of Energy. Storage . The team noted that a follow-up study that applied the tools developed in the work in a techno-economic optimization could pave the way to implementation, identifying the ideal operation and sizing for the lowest cost and maximum revenue. Another research team from the Technical University of Denmark investigated this year what levelized cost of storage (LCOS) Carnot batteries need to be competitive in a 100% renewable scenario in their country. They concluded that an LCOS lower than 66.2 euros/MWh would be competitive, as long as gas prices remained at low levels. |
