Based on the heat pump-organic Rankine cycle, scientists in Portugal have made six different models of Carnot batteries for stationary storage. They investigated 16 different combinations of working liquids and created a multi-objective optimization for the best candidate.
Researchers from Portugal’s University of Coimbra have designed various versions of heat pump-organic Rankine cycle-based Carnot batteries (CBS).
Carnot are batteries Systems that store electricity in the form of heat by storage media such as water or melted salt and transform the heat back to electricity when needed. This category includes Systems Laes systems (LAES) Systems) and BRAYTON or Rankine-based Thermal Energy Storages (PTS) systems, as well as Lamm-Honigmann storage, a sorption-based technology that can be charged and unloaded with both heat and electric power, and systems.
All these storage technologies make a wide range of applications possible, such as arbitration activities, supporting services or peaks within Power networks.
The scientists simulated different systems through optimization with one objective and multi-objective optimization for energetic, exergetic and economic efficiency, with the help of 16 different combinations of environmentally friendly work fluids.
“A CB is an energy-to-heat-to-power energy storage technology that converts excess electricity into thermal energy by heating or cooling a thermal energy storage system.” The CB is divided into three thermal sectors: the TES tanks (high temperature and low temperature), the heat sector and the cossack lecture. “
The team presented six HP-Orc combinations that works as a CB. System 1 is the most basic system, including a vapor compression arm pump (VCHP) and a simple ORC. System 2 adds a regenerator to the HP, system 3 adds a regenerator to the ORC and System 4 adds regenerators to both the HP and the ORC. System 5 uses a two -stage heat pump with a flash room, while System 6 two -stage HP and a regenerative ORC.
Four different working liquids were tested on both the HP and the ORC sides, which resulted in a total of 16 possible combinations. In particular, they were R1224YD (Z), R1234ze (Z), R1336MZZ (Z) and R1233ZD (E). The systems were developed in Matlab 2024A, based on a steady-state effect for the VCHP and ORC; no heat losses and pressure losses with heat exchangers; Compressor and expander constant efficiency; Water as a heat transfer fluid in the heat source, storage and cold source.
Firstly, optimization with one objective was initiated for all possible combinations of the six system configurations and the 16 working liquid pairs. Each combination has three single-objective optimisations through-energy, exergetic and economic. A new score method was applied to systematically identify the optimum configuration pair of the work fluid.
The simulations showed that the regenerative heat pump and ORC configuration (system 4) consistently produced the best results for all liquid combinations, which demonstrated the suitability for this technology compared to other systems, with R1233ZD (e) -R1233ZD (Z) followed by R1234ZE followed by R1234SE followed by R1234ZE the R1234SE followed by R1234SE (Z) the R1234ZE’s), followed by R1234Ze (Z) the R1234Ze (e) -R124S14S14S14S14S1s4S1s4Z234Z234S1s. shows. The basic heat pump and ORC configuration (system 1) with R1336MZZ (Z) -R1336MZZ (Z) turned out to be achieved the lowest performance. “
After this analysis, the group carried out the multi-objective optimization for system 4, using R1233ZD (E) on both HP and ORC sides. According to their findings, a trade-off between return efficiency and the Livalized storage costs (LCOs). The optimum design nevertheless achieved a Round trip efficiency of 57.43% and an LCOs of € 0.649 ($ 0.73)/kWh.
“Higher efficiency up to 81.30% was possible without significantly jeopardizing general performance. After this point, further improvements are not justified due to rapid relegation of performance,” the team said. “The optimum design point corresponds to a LCOS of € 1,093/kWh for a small -scale experimental test installation, but is expected to decrease on larger scales.”
Their findings were presented in “Multi-objective optimization and design of a carnot battery for energy storage applications“Published in Energy conversion and management: X.
In a study published in 2023, academics from the Technical University of Denmark suggested using Carnot batteries to convert coal -fired power stations into renewable energy.
Another group of researchers in Denmark also investigated how carnot batteries can be used to store renewable energy in their home country and have established that these devices can only make an important contribution under a certain cost threshold.
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