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Scientists have designed a new building-integrated PV system that uses 30 mm of phase change material on each side of the wall. The array reportedly achieved superior thermoelectric coupling performance compared to reference BIPV systems without PCM.
Researchers from China have designed a novel building-integrated photovoltaics (BIPV) system that integrates a layer of phase change material (PCM) on each side of the wall.
Dubbed double-PCM BIPV composite envelope (BIPV-dPCM), the new system was experimentally validated via a numerical model and was compared to reference systems. Per the results, it achieved superior thermoelectric coupling performance compared to all of the other systems.
“The integration of PCM with BIPV presents a compelling approach to enhance solar energy utilization and mitigate indoor thermal loads, contributing to energy-efficient and low-carbon building development,” said the scientists. “The PCM can reduce the PV operating temperature and reduce the peak load difference, while reducing the indoor air temperature fluctuation.”
The proposed system, which was simulated using the TRNSYS software, is composed of several layers. First, monocrystalline silicon PV modules are placed on the outer layer, which are then coupled with 30 mm of RT-28 PCM. That is followed by 10 mm thick cement mortar, 120 mm of brick wall, and another 10 mm of cement mortar. Finally, a 30 mm thick RT-40 PCM is placed on the inside of the apartment.
“During the day, the PV panels convert solar radiation into electricity, generating excess heat that is directed toward the indoors,” the academics explained. “The PCM affixed to the back of the PV panels absorbs heat, which causes it to melt, thus reducing the PV temperature and improving power generation efficiency. At night, the PCM near the indoor area begins to solidify and thus exothermic, thus maintaining the indoor temperature with small fluctuations. The double PCMs enhance the thermal resistance of the wall, preventing heat transfer between the inner and outer layers.”
This system was simulated to be in a south-facing room of 5 meters in dimension, located on the middle floor of a civil dwelling in Guangzhou, China. One person was assumed to live in this room, using 3.8 W/m2 of light and 5 W/m2 of other equipment. The lights were assumed to be on from 1 a.m. and 2 p.m., and the other equipment was in use between 7 a.m. and 9 p.m. Air conditioning was turned on during the summer months between 7 a.m. and 5 p.m. and and set to a temperature of 26 C.
“To verify the proposed new BIPV-dPCM envelopes capability of considering both power generation and thermal insulation performance, the study compares it with three other typical envelopes,” said the researchers. “The reference wall is named Wall I, while Wall II is a common single-layer PCM coupled with a PV enclosure structure that shows better power generation performance when close to the PV panels. Wall III shows better thermal insulation performance when close to the interior. The proposed BIPV-dPCM in this study is named Wall IV.”
The analysis showed that the novel system achieved a cold load reduction of 7.94%, 4.60%, and 0.50% less than structures I, II, and III respectively. It enhanced temperature control and reduced PV peak temperatures by 1.77 C and inner wall temperatures by 6.3 C, delaying heat penetration by 1 hour.
“The exergy analysis of the four types of enclosure structure shows that the double PCMs can more effectively improve the overall exergy efficiency and reduce the exergy damage of each component,” the group added. “However, the internal exergy loss of the PV module accounts for more than 80%, so it is necessary to incorporate cooling techniques such as ventilation.”
Concluding the results, the scientists said that “the self-sufficiency coefficient (SSC) of the BIPV-dPCM system is closely related to the phase transition time of the PCM. The SSC can exceed 55%, showing a strong PV self-consumption capability. By optimizing the parameters, especially the PCM thickness ratio, the SSC can exceed 65%.”
The system was presented in “Investigation of double-PCM based PV composite wall for power-generation and building insulation: thermal characteristics and energy consumption prediction,” published in Energy and Built Environment. Researchers from Chinas Jinan University, Anhui University of Technology, and Wuhan University have conducted the study. |
