A concentrated photovoltaic/thermal system employing micro-channel heat pipes and thermoelectric generators is constructed. Photovoltaic cells and thermoelectric generators are used to generate power, and the heat is gained by the circulating water. The feasibility of the system is demonstrated by the experimental work which compensates for the lacked experimental content in our previous paper and validates the correctness of the established mathematical model. Additionally, using the validated model, the influence of the addition of a glass cover and the volume of the water tank is investigated by simulation discussion, and the annual prediction is conducted. The results indicate that, during the 4-h actual operation, the electrical power of thermoelectric generators first increases and then decreases with the average value of 8.33 W, effectively improving the average electrical efficiency of the system from 7.62% to 8.95%. Also, the water tank temperature is incremented from 32.89 degrees C to 45.28 degrees C. The addition of a glass cover increases the heat gain but reduces the total electrical output because of the weakened PV performance. The large-volume water tank detracts from the final temperature but is helpful to the electricity. Therefore, it needs to compromise in respect of either great electrical performance or thermal performance.

The concentric double-tube heat exchanger (CDTHE) proposed in our previous work addresses the limitations of the combined application of conventional loop thermosyphon photovoltaic/thermal (LT-PV/T) systems. Based on this, a novel non-concentric multi-tube heat exchanger (NMTHE) as the condenser of the LT-PV/T system was proposed in this paper, which improves the performance of system by reducing the flow resistance of the working fluid. Experimental platform was built to explore the performance difference between CDTHE-LT-PV/T and NMTHE-LT-PV/T system. Experimental results show that compared with the CDTHE-LT-PV/T system, the thermal efficiency, the electrical efficiency, the primary energy-saving efficiency and the exergy efficiency of NMTHE-LT-PV/T system relatively increase by 17.76%, 2.1%, 10.05% and 3.64%. Mathematical models for two systems are established and verified. Then the performance of the two systems under different solar radiation and ambient temperature is explored. Besides, the all-day performance of the two systems on typical winter days in four cities at different latitudes is predicted. The results show that the NMTHE-LT-PV/T has more prominent advantages in northern China at higher latitude. Furthermore, the influences of some structural parameters and operating setup on the performance of NMTHE-LT-PV/T system are discussed.

As is well known, traditional solar systems can only work under conditions of solar radiation, as solar energy is the sole energy source for photovoltaic generation and heat recovery. Few studies have focused on their continuous operation throughout the day and this research gap needs to be filled. Consequently, to pursue a round-the-clock electrical power generator, in this study, a two-stage system is constructed, consisting of the first-stage photovoltaic/thermal module and the second-stage solar thermal collector with thermoelectric gen- erators in series. Thermoelectric generators ensure that the system runs normally by day, while also utilizing the heated fluid to achieve uninterrupted energy output at night. A numerical model of the system is developed to analyze the performance changes under continuous running. From the results, the second-stage module improves the daytime heat gain, effectively boosting the electrical contribution of thermoelectric generators, whether during the day or night. At the maximum input energy, photovoltaic cells generate the greatest power of 118.37 W with an average efficiency of 14.56%. The average efficiencies of thermoelectric generators in the daytime and nighttime are 0.97% and 0.53%, enhancing the total electrical output. Additionally, the comparative analysis is performed under different parameters, as well as an economic analysis.

The utilization potentiality of PV/T which laminates PV onto glass cover to improve reliability (G-PV/T) was proved previously, but how to optimize the structure is not comprehensive. This study focuses on its optimization and energy trade-off among two critical structural parameters (i.e., packing factor, air gap thickness). Firstly, mathematical models for G-PV/T are established and validated by the experimental data. Specifically, a special G-PV/T without air gap is also considered, and where its' difference in optical models and heat transfer models are stated. Secondly, the past studies of PV/T used to investigate parametric optimization by discussing only one parameter at a time, but this study points out that the optimization methods for these structural parameters are interrelated, and their coupling relationship is influenced by outside conditions. So a matrix of the two parameters is used to predict the daily performance of G-PV/T and the results are presented in three-dimensional two-independent-variables plots, evaluated by the first and second laws of thermodynamics. Suggestions are given for structural optimization depending on application requirements and energy trade-off. Thirdly, performance under three important outside conditions is predicted to discuss how the system performance is influenced and how the coupling relationship of the two critical parameters moves.

The condensers of loop thermosyphon PV/T systems (LT-PV/T) are usually integrated inside water tanks, which may bring some challenges during combination use. This research innovatively proposed a concentric copper tube heat exchanger as the condenser, which is combined with a copper tube evaporator beneath the absorber. The gaseous working fluid flows in the inner tube and the cooling water flows in the outer tube. Since ordinary water pipes are used for water circulating between the outer tube and water tank, this LT-PV/T collector can be used individually or combined with other collectors flexibly. To access its' performance, researches have been conducted: (1) Designing and fabricating the system prototypes; (2) Investigating system performance with different volume-filling ratios (26.5%, 34.8%, 43.2%); (3) Investigating the influences of working fluid (water, ethanol and R134A). (4) Evaluating the systems’ performance with energy efficiency, exergy efficiency, and semi-empirical system efficiency models; (5) Conducting two case studies in South China (an individual collector & a 4 parallelly/serially-combined LT-PV/T collectors system). The system is first-of-its-kind and has obvious advantages in reliability, flexibility, space-saving and large-scale applications. The typical primary energy-saving efficiency of the LT-PV/T with R134a of 40% filling ratio can reach 78.0%, higher than the published LT-PV/T systems.