• Energy Research

Abstract The double-skin facade (DSF) has considerable potential in solar energy utilization. Adding the functions of conventional DSFs is of great significance to building energy saving. Moreover, the purification of indoor air is becoming a popular topic with the increase in the requirements for a healthy living environment. In this work, a photocatalytic CdTe double-skin facade (PCPV-DSF) based on the mechanism of solar spectrum-splitting utilization was proposed. This technology could realize the functions of air purification, electricity generation, space heating, thermal insulation, and daylighting. The simulation model of the proposed system was developed and verified. The weather sensitivity and comprehensive energy performance of the proposed system were analyzed using this model, and the comparison between the PCPV-DSF and conventional PV-DSFs was performed. The main results are: (1) The solar radiation had a larger impact on the proposed system than ambient temperature and wind speed. (2) The PCPV-DSF system could reduce electrical energy consumption by 229 kWh/m2, and generate clear air by 7014 m3/m2 in a cold region. (3) Compared with the PV-DSFs with built-out and built-in PV glazing, the proposed system had a superior thermal insulation effect, and could save 114 kWh/m2 and 25 kWh/m2 electrical energy, respectively.

Abstract In flat-plate PV/T systems, there are some contradictions in the temperature requirements for the heat and electricity acquisition. The widely-used crystalline-silicon solar cells are negatively affected by the high temperature inside the PV/T collector. This paper proposes to use temperature-insensitive solar cells in PV/T and the CdTe used has the advantages of low power temperature coefficient, high photovoltaic efficiency, and low costs. Besides, the sandwich structure that CdTe cells are sealed between two pieces of glass can prevent them from the permeating of moist air. The CdTe-PV/T is experimentally tested and compared with a Poly-Si-PV/T system and it exhibits better instantaneous electrical performance at high operating temperatures and gains more electrical energy throughout the day. Then the influence of cells’ coverage ratio is investigated experimentally and the result shows that a higher coverage ratio is beneficial to the electrical and energy-saving performance. Furthermore, a new quasi-steady-state mathematical model is established and verified. Parametric discussions are conducted for performance optimization. The black TPT coating with higher emissivity performs better than the selective absorption coating of the absorbing plate, contrary to the traditional PV/T collector. The heat transfer mode between the back glass and the absorbing plate is different in different thicknesses of the air gap. Reducing the thickness can effectively improve the system’s performance in terms of thermal, electrical, and temperature. Then an improved CdTe-PV/T eliminating the backglass and air gap is proposed and numerically simulated. This research hopes to provide some ideas for the applicant and the optimization of CdTe-PV/T in hot climates.

Abstract CdTe cells have many advantages such as high electrical efficiency, and low cost. Few studies on PV windows combined with CdTe cells exist. The PV windows investigated in the past were mainly designed for cooling needs. In this work, a double-skin ventilated window integrated with CdTe cells (CdTe-DSV) was proposed, which could meet seasonal thermal demands. A mathematical model of the proposed window was developed and validated against experimental data. Based on the model, firstly, the thermal comfort in a building with the proposed window was discussed. Secondly, the energy performance (including heat, daylight, PV output) of the proposed window was analyzed and compared with that of the a-Si-DSV window. Finally, the effects of cavity depth, and PV coverage ratio on energy performance were evaluated. The results indicated that the CdTe-DSV window could ensure a relatively neutral thermal sensation. The energy saving of heat transmission in winter and summer was 205.76kwh and 333.09kwh respectively. The CdTe-DSV window had a higher PV output than the a-Si-DSV window by 62%. The increase of PV coverage can decrease the cooling load and increase the heating load. Increasing the air cavity depth is always beneficial to energy saving.

Abstract In this work, a double-skin ventilated window integrated with CdTe cells was proposed, which can adapt to various climate conditions by switching the work modes. Firstly, the experiment of testing the thermal and electrical behaviors of this window was conducted on an actual building. Secondly, the simulation model coupling this window with the building was developed and validated against the experimental data. Thirdly, the annual performance of the proposed window (including heat, daylight, PV output) in typical climate regions of high, middle, low latitudes was predicted. Finally, the impact of change in parameters on the energy performance was analyzed. The experimental results showed that the proposed window could provide the hot air to the room under winter mode, and effectively reduced solar heat gain under summer mode. The PV efficiency was greatly affected by solar incident angle. The simulated results indicated that the electricity loss due to the extinction and reflection of glass was about 25%-30%. For Hefei and Harbin, the most energy-efficient orientation of the proposed window was south, and it was west for Haikou. As the PV coverage ratio increased, the net energy consumption decreased firstly and then increased. The optimal values for Harbin, Hefei, and Haikou were 50%, 60%, and 70%, respectively. Increasing the window-wall ratio and the cavity depth was always beneficial to reduce NEC.

Abstract PV/T systems are developed to obtain electrical & thermal energy simultaneously. Generally, in PV/T system where PV cells are laminated on absorbing plate (A-PV/T), the cells can be damaged due to high temperature, thermal stress, electrical insulation problem and absorbing plate deformation. Consequently, the reliability of PV cells limits the wide application of A-PV/T systems. Moreover, the electrical performance is affected by high cells’ temperature. To overcome these problems, proposed a new structure of a PV/T system where cells are laminated on the back of glass cover (G-PV/T) instead. Experimental and numerical investigations are performed to explore the performance of two systems. The G-PV/T shows a lower temperature and better photovoltaic performance with the daily electrical efficiency of 11.66% (which of A-PV/T is 9.74%), thermal efficiency of 28.4%, and final water temperature of 45.6 °C. Two 3D dynamic thermal/electrical models are also proposed, which shows good agreement with experimental data. The influences of various structural parameters (PV coverage ratio, thickness of absorbing plate, thickness of air gap) on both PV/T systems have been predicted and compared. Furthermore, two mechanical models are proposed to explore the thermal stress distributions across the cells as well as provide an economic analysis of two systems.

Abstract In this paper, a photovoltaic direct-driven ice storage air-conditioning (PDISAC) system is proposed and performance of the system is experimentally and theoretically investigated. The proposed system is a battery or inverter less photovoltaic direct-driven system where the DC compressor is directly connected to the PV array. Through the test, it has been found that the proposed system was able to lower the test room temperature below 298.15 K, while the reference room temperature was 306.15 K. Moreover, the experimental refrigeration efficiency and solar-energy utilization efficiency were reported 1.028 and 7.1% respectively. Then, a mathematical model for the progress of ice making and cold storage is presented and verified by the experimental results. Besides, the factors such as the ambient temperature, the initial water temperature and volume in the ice storage tank, and the thickness of the ice layer surrounding the coil have been studied. The simulation results indicate that the initial heat transfer rate at the condensation side drops by 10.8% and refrigeration efficiency drops by 32.7% with the ambient temperature increasing from 298.15 K to 308.15 K. The increment of initial water temperature and initial water volume will lead to an increase in refrigerating capacity and refrigeration efficiency.