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Scientists have designed a new building-integrated photovoltaic system that uses 30 mm of phase-change material on each side of the wall. The array has reportedly achieved superior thermoelectric coupling performance to reference BIPV systems without PCM.
Chinese researchers have designed a novel building-integrated photovoltaic (BIPV) system that integrates a layer of phase-change material (PCM) on each side of the wall.
Named BIPV-dPCM composite envelope, the new system was experimentally validated using a numerical model and compared with reference systems. According to the results, it achieved superior thermoelectric coupling performance than all other systems.
“The integration of PCM with BIPV presents a compelling approach to improve solar energy utilization and mitigate indoor thermal loads, contributing to the development of energy-efficient and low-carbon buildings,” the scientists say. “PCM can reduce the operating temperature of PV and decrease the peak load difference, while reducing indoor air temperature fluctuation.”
The proposed system, which was simulated using TRNSYS software, consists of several layers. First, monocrystalline silicon photovoltaic modules are placed on the outer layer, which are then coupled with 30 mm of RT-28 PCM. Next, 10 mm of cement mortar, 120 mm of brick wall and another 10 mm of cement mortar are laid. Finally, a 30 mm thick RT-40 PCM is placed inside the apartment.
“During the day, the photovoltaic panels convert solar radiation into electricity, generating excess heat that is directed towards the interior,” the academics explain. “The PCM placed on the back of the photovoltaic panels absorbs the heat, causing it to melt, thereby reducing the photovoltaic temperature and improving the efficiency of power generation. At night, the PCM close to the interior zone starts to solidify and therefore exotherm, thus maintaining the interior temperature with small fluctuations. The double PCM increases the thermal resistance of the wall, preventing heat transfer between the inner and outer layers.”
This system was simulated in a 5-meter south-facing room on the middle floor of a civilian dwelling in Guangzhou, China. This room was assumed to be inhabited by one person, who used 3.8 W/m2 of lighting and 5 W/m2 of other equipment. The lights were assumed to be on between 1 a.m. and 2 p.m., and other equipment was assumed to be used between 7 a.m. and 9 p.m. The air conditioner was turned on during the summer months between 7 a.m. and 5 p.m. and was set to a temperature of 26 ºC.
“To verify the ability of the proposed new BIPV-dPCM envelope to take into account both power generation and thermal insulation performance, the study compares it with three other typical envelopes,” the researchers explain. “The reference wall is referred to as Wall I, while Wall II is a common monolayer PCM coupled with a PV enclosure structure that shows better power generation performance when close to the PV panels. Wall III exhibits better thermal insulation when close to the interior. The BIPV-dPCM proposed in this study is referred to as Wall IV.”
The analysis showed that the new system achieved a cooling load reduction of 7.94%, 4.60% and 0.50% less than structures I, II and III, respectively. It improved temperature control and reduced peak PV temperatures by 1.77 C and interior wall temperatures by 6.3 C, delaying heat penetration by 1 hour.
“The exergy analysis of the four types of enclosure structure shows that 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.”
As a conclusion of the results, the scientists stated 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%, which demonstrates a strong photovoltaic self-consumption capacity. By optimizing the parameters, especially the thickness ratio of the PCM, 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 Jinan University in China, Anhui University of Technology and Wuhan University conducted the study. |
