Energy storage technology can effectively overcome the volatility and instability of solar energy resources, alleviate the imbalance between energy supply and demand, and improve the stability and flexibility of system operation. In order to reduce the energy storage cost of solar thermal power plant energy storage systems, this article chooses to use alternative solutions such as concrete energy storage systems and packed bed energy storage systems. Elaborated on the heat transfer characteristics of different energy storage systems, calculated their thermal storage performance, and established a technical and economic model to evaluate the economic feasibility of different schemes. The main conclusions are as follows:
(1) Based on the heat transfer characteristics of different energy storage systems, transient heat transfer models for concrete energy storage systems and packed bed energy storage systems were established based on solid heat transfer theory and local non thermal equilibrium theory of porous media. The heat storage mechanisms of concrete sensible heat storage systems and phase change packed bed energy storage systems were revealed. By verifying the consistency between numerical calculation results and experimental data, the effectiveness of different energy storage models was verified, providing a basis for the thermal performance analysis of energy storage systems.
(2) The optimal scheme for the overall thermal performance of the concrete energy storage system was proposed, and the optimization strategy for the structure and operating parameters of the concrete sensible heat energy storage system was obtained. A quadratic regression model was established between the main design factors and thermal storage time, energy storage, and energy storage efficiency using response surface methodology. The main factors affecting thermal storage performance were tested using analysis of variance. In addition to single factors, the interaction between different factors can also have a significant impact on the thermal storage performance indicators of the system. Fluid velocity is the most important factor affecting heat storage time and energy storage efficiency, and fluid inlet temperature is the most important factor affecting energy storage. In the interaction, the interaction between fluid inlet temperature and flow velocity has a significant impact on heat storage time, while the interaction between the number of pipes and fins has a significant impact on energy storage and efficiency. When the volume of pipes and fins accounts for 1.25% and 1.13% of the volume of concrete energy storage systems, the overall thermal performance of the system is optimal. An increase in the number of pipes in the energy storage module will enhance heat transfer, but if the number of pipes exceeds a certain amount, the decrease in fluid flow velocity in the channel will lead to a more significant decrease in heat transfer rate.
(3) The effects of fluid flow rate, operating temperature range, and volume fraction of phase change materials at different phase change temperatures on the thermal performance of packed bed energy storage systems were revealed. The influence of concrete volume fraction on the thermal performance of a combined sensible latent heat energy storage system was studied. In order to utilize the heat transfer of fluids with different temperature gradients, a three-layer phase-change packed bed energy storage system is used. Except for the high-temperature PCM-H energy storage system, the three-layer PCM-T energy storage system has a higher energy storage efficiency than other single phase change packed bed energy storage systems. Increasing the fluid flow rate and operating temperature range can improve the energy storage rate of the packed bed energy storage system, but the impact on energy storage efficiency is relatively small. The increase in flow rate mainly accelerates the convective heat transfer between the fluid and phase change materials, and a higher operating temperature range increases the inlet temperature, both of which are beneficial for reducing the system’s heat storage time. In a three-layer phase-change packed bed energy storage system, as the volume proportion of high-temperature phase-change materials increases, the system’s energy storage and heat acquisition from the fluid increase, but the energy storage rate decreases. The impact of different volume ratios of phase change materials on energy storage efficiency is relatively small. In order to reduce energy storage costs, a combination of sensible and latent heat is used to fill the bed energy storage system. As the proportion of concrete volume increases, the energy storage of the system decreases more significantly, the energy storage rate increases, and the energy storage efficiency decreases.
(4) The combination of sensible and latent heat energy storage system was identified as the best alternative solution, taking into account both energy storage efficiency and energy storage rate requirements. The concrete integral value for minimizing the energy storage cost of the sensible and latent heat combination system was determined. By comparing the energy storage costs of different systems, it was found that the dual tank molten salt energy storage system has the highest unit energy storage cost, and the sensible latent heat combined packed bed energy storage system is an ideal alternative solution. Taking into account the unit energy storage cost, energy storage rate, and storage capacity of the system comprehensively
Factors such as energy efficiency, 50% concrete volume fraction is the optimal choice. Compared to the dual tank molten salt energy storage system, using the C-X1 energy storage system can reduce the unit energy storage cost by 30.1%.
(5) Obtain the sensitivity variation pattern that affects the unit energy storage cost of different energy storage systems. Through sensitivity analysis of the factors affecting the unit energy storage cost of different energy storage systems, it was found that the material cost of the tank is the most sensitive factor in the dual tank molten salt energy storage system. A 20% reduction in the material cost of the tank can reduce the unit energy storage cost of the system by 11.5%. In high-temperature concrete energy storage systems, the high cost of insulation materials has the greatest impact on the unit energy storage cost of the system. The cost of insulation materials is reduced by 20%, and the unit energy storage cost of concrete energy storage systems is reduced by 10.7%. For phase-change packed bed energy storage systems, the high temperature phase-change materials in PCM-H systems have a higher price, which has the greatest impact on the unit energy storage cost of the system. Among other phase change packed bed energy storage systems, packaging cost is the most sensitive factor affecting the unit energy storage cost of the system. For the C-X1 energy storage system, the cost of tank materials has the greatest impact on the unit energy storage cost of the system, while the cost of concrete materials has the smallest impact.
(6) We have established a technical and economic model suitable for calculating energy storage systems of different photothermal power plants, and evaluated the economic feasibility of various energy storage systems under different installed capacity scenarios of photothermal power plants using deterministic and stochastic methods. The analysis results show that compared to the dual tank molten salt energy storage system, using concrete sensible heat storage, phase change packed bed energy storage, and a combination of sensible and latent heat storage systems are economically feasible. Considering the uncertainty of parameters in the stochastic model, sensitivity analysis reveals that capacity factors and nominal interest rates have the most significant impact on the system LCOE. As the scale of energy storage systems expands, LCOE gradually decreases. The uncertainty premium of the quantitative system and the deterministic equivalent of the C-X1 system are 0.1852 $/kWh and 0.1321 $/kWh, respectively, making it still the most economically efficient energy storage system in research. In addition, introducing the environmental and social benefits of carbon reduction and transforming them into economic benefits further reduces the LCOE of various energy storage systems, highlighting their importance in improving economic efficiency.
Analyze the heat transfer characteristics of different energy storage systems in solar thermal power plants and determine the key factors affecting the thermal performance of energy storage systems. Through cost analysis, the energy storage costs of different energy storage systems were compared, and the sensitivity of factors affecting energy storage costs in different systems was obtained. Evaluate the economic performance of different energy storage systems using technical and economic models to obtain the power generation costs of different energy storage systems. Consider the uncertainty of input parameters and quantify the deterministic equivalence of different energy storage systems. Based on the above research, further research can be conducted from the following aspects:
(1) At present, the technology of high-temperature concrete energy storage and phase change filled bed energy storage is still in the exploratory stage, and the experimental cost is relatively high. Most studies use numerical simulation methods, and actual experimental support data is limited. In the future, relevant experimental platforms can be built for different energy storage systems to provide experimental data support and mutual verification for the simulation process.
(2) Conduct dynamic performance studies on different energy storage systems. When studying the energy storage process of different energy storage systems in this article, the working conditions are determined. In order to approach the real situation more closely, subsequent research can consider the dynamic operation law of energy storage systems that changes with external conditions, providing reference for the optimization of actual operation plans.
(3) Expand research objects from energy storage systems to the entire solar thermal power plant. The energy storage system is an important component of solar thermal power plants, but it cannot fully reflect the power generation situation of the entire solar thermal power plant, and cannot be directly compared economically with traditional power plants. Therefore, when considering the energy storage system, simulating the operation of the entire solar thermal power plant and calculating the overall power generation cost of the solar thermal power plant can provide a more comprehensive understanding of the economic efficiency of the entire system.