Evaluation of dual-tower optical efficiency limit for guiding the design of solar power tower systems

Although dual-tower solar power tower systems may offer potential optical performance advantages, their practical performance is affected by many coupled engineering factors, including shadowing and blocking losses, finite heliostat size, optical errors, receiver flux constraints, land occupation, and operational constraints, among others. Therefore, the actual performance of a practical plant does not directly reveal the intrinsic geometric-optical potential of the dual-tower configuration itself. Motivated by this, this study develops an idealized geometric-optical upper-bound model for the optical efficiency limit of dual-tower systems. The objective is not to provide directly deployable engineering layouts or quantitative design recommendations, but to establish a comparable upper-bound benchmark for revealing the intrinsic optical potential of the configuration and supporting rapid upper-bound assessment at the conceptual stage. The model systematically examines the effects of latitude, tower height, receiver radius, total heliostat area, and tower spacing on the dual-tower optical efficiency limit. The results show that, as tower spacing increases, the optical efficiency limit exhibits a transition from enhancement to degradation, indicating the existence of an upper-bound optical optimum tower spacing under the prescribed assumptions. Furthermore, based on 26,472,600 simulated samples, an explicit symbolic-regression predictive equation is developed, achieving an R² of 0.9339 and a mean APE of 1.10% in repeated random evaluations; the P90 and P95 APEs over the full parameter space are 2.19% and 2.87%, respectively. These results provide an idealized geometric-optical upper-bound reference for understanding the dual-tower configuration.