Carnot battery systems have the advantages of high efficiency, low investment cost, long lifespan, and minimal geographical constraints, making them a promising technology for large-scale energy storage. In this work, thermo-economic models of Joule-Brayton cycle-based Carnot battery systems with packed-bed sensible thermal storage (J-B-PB) and liquid thermal storage (J-B-LTS), as well as a heat pump-organic Rankine cycle-based (HP-ORC) Carnot battery system, were developed, and multi-objective optimization and parameter analysis were conducted for the three systems. Additionally, multi-criteria decision-making methods were employed to determine the optimal system configurations and working fluids under different decision preferences. The results indicate that the optimal solutions for different system configurations and working fluids, revealing a trade-off between round-trip efficiency (chi) and levelized cost of storage (LCOS). The J-B-PB system with helium has the lowest LCOS, reaching 0.178 $& sdot;kWh-1 at a chi of 39.50 %, while the J-B-LTS system with nitrogen achieves the highest chi of 58.47 % at a LCOS of 0.323 $& sdot;kWh-1. For the HP-ORC system, R1234ze(Z) and R1233zd(E) exhibit superior performance. The working fluid pressure, temperature and Thermal storage temperature Tstin charge and discharge loop have significant influence on system performance, with optimal values depending on the configurations and working fluids. MCDM results show that decision criteria influence the selection of optimal configurations and working fluids. When economic considerations dominate, the J-B-PB system with helium is preferred, while prioritizing chi favors the HP-ORC system with R1224yd(Z). Besides, four MCDM methods are compared, and LINMAP is chosen as the most suitable MCDM method for Carnot battery systems due to the highest Borda ranking score (0.9987) and the highest average correlation coefficient (0.9702).

This study proposes a new combined cooling, heating and power (CCHP) system applied for geothermal energy. In the proposed system, a water heater is introduced to utilize the exhaust geothermal water for supplying heating, and the throttled valve of the basic flash cycle is replaced by an ejector for cooling output. To evaluate the system performance, detailed mathematic models are established and validated. Based on the basic condition (170°C geothermal water), the exergy efficiency of the proposed system is 44.34% and the sum of the power, cooling output and heating output is 10,283.68 kW. Also, the exergy loss analysis demonstrates that the component of the water heater, ejector, turbine, condenser and flasher has a large improved space to reduce the exergy destructions for system performance enhancement. At last, the parametric analysis results suggest that there exists an optimal flash pressure (around 140 kPa) to maximize the exergy efficiency. Within the discussed ranges, both the increase of the outlet temperature of water heater and condenser temperature will damage the system exergy efficiency, while a higher evaporator temperature is beneficial for the system exergy efficiency.

The electric regulation capacity of heating units has been constantly improving due to the promotion of the heating units’ flexibility transformation. This improvement has effectively alleviated the long remained serious wind and light abandonment phenomena in the heating season in China. In this paper, we discussed the key technologies of the low pressure zero output heating mode and bypass heating mode, both of which are widely used in thermo-electric decoupling. Moreover, the coupling transformation of the two heating modes has been successfully realized in a heating unit. The electric regulation capacity of the unit has been greatly improved, from 18.6% before the transformation to 66.7%, and the minimum technical output has been also reduced to 14.2% THA. After the transformation, the unit now is able to provide several heating modes with its operational flexibility greatly improved. By comparing the economical efficiency of these heating modes, we obtained the operation mode with the lowest heat rate. This transformation mode provides a huge grid space for the consumption of clean energy, so it is of positive reference value and exemplary significance in implementing the flexibility transformation of heating units.

To overcome the strong thermoelectric coupling in a coal-fired combined heat and power plant (CCHPT), three optimization schemes are investigated. These include low-pressure turbine little steam operation (LLPEH), extracting steam from high pressure turbine (HP-LPEH), and integrating the LLPEH and HP-LPEH (HP-LLPEH). These are employed for enhancing the plant's heat and electricity supply flexibility using steam extracted between the intermediate- and low-pressure turbines to provide heat (LPEH). The thermodynamic and economic performance of the schemes when applied to a 330MW coal-fired combined heat and power plant were evaluated and compared. The comparison reveals the highest heat supply capacity, highest heat to electricity ratio, and lowest standard coal consumption for the HP-LLPEH scheme, while the LPEH exhibits the highest thermal efficiency.