A method for evaluating both shading and power generation effects of rooftop solar PV panels for different climate zones of China
Abstract: The photovoltaic (PV) roofs have two main energy-saving effects, which are shading and power supply. Considering the shading and power generation gain jointly, a roof is changed from the building energy end to the building energy supply end, thus changing its energy use system greatly. Therefore, this paper carries out research on the comprehensive energy-saving effect integrating the shading and the power supply gain. Three types of PV rooftops, namely, horizontally-mounted overhead PV rooftop, tilted overhead PV rooftop, and attached PV rooftop are studied to explore their impacts on the heat gain and heat loss of the roof and building’s heating and cooling load. In order to estimate the overall energy-saving in different climatic regions in China, an overall energy-saving evaluation method that considers the power generation and shading benefit effects of the PV rooftop is proposed. Based on the climate and solar radiation zones in China, 13 respective cities are selected to be included in the research. The results show that, by considering only the shading effect of PV panels, the tilted PV is more suitable in summer, reducing the heat input, whereas the horizontally-mounted PV is more effective in winter to prevent more heat loss. Regarding the overall energy-saving that considers both the shading and power generation effects of PV panels, building with horizontally-mounted PV rooftop has the highest efficiency in the summer season, while the building with tilted PV rooftop has the highest efficiency in the winter season. The model and analysis of the overall energy-saving presented in this work can provide a guide for the application of rooftop solar PV panels in different climate zones in China.
Summary (2 min read)
- Due to the conventional energy shortage and environmental deterioration, the development and utilization of renewable energy have become inevitable in order to overcome the current energy crisis.
- Since PV panels are most commonly installed on building rooftop (Oliver and Jackson, 2001), numerous studies on the energy-saving performance of PV rooftop have been conducted.
- By substituting the comprehensive air temperature into the Eqs. (14) and (15), the indoor heat gain (heat loss) and heating load of the roof can be obtained, respectively.
- In order to illustrate the influence factors to the overall energy-saving efficiency, the test data were analyzed using SPSS 26.0.
3. Experimental results and model validation
- Therefore, the surface temperature at night of the PV rooftop was generally higher than that of the ordinary roof, and the effect of horizontal overhead PV roof is more obvious.
- This was mainly because the upper surface of the control body of the attached PV module received all solar radiation, just like the ordinary roof.
- 3. Heating and cooling load results 8. Compared with the ordinary roof, the heat gain caused by the short-wave solar radiation of the PV roofs was sheltered, and the heat loss caused by the PV roof’s long-wave radiation was reduced.
4. Analysis and discussions of overall energy-saving performance
- The overall energy-saving efficiency of a PV roof is affected by both outdoor air temperature and solar energy resources.
- In areas with hot summer and cold winter, the daily total heat loss and the peak heating load of the firmly-attached PV roof are higher than those of the ordinary roof.
- The overall energy-saving efficiencies of the selected cities in the winter are shown in Fig. 16.
- Also, the heat insulation of the PV modules was stronger than the shading effect.
- On the other hand, in the winter, the solar radiation on the inclined surface is higher than that on the horizontal surface, compared to the horizontally-mounted overhead PV roof, the tilted overhead PV roof obtained heat more.
- In addition, 13 typical cities in 5 climatic regions of China are selected for the investigations to evaluate the overall energy-saving performance of three PV roof types.
- The roof with a horizontal PV had the highest efficiency of 0.32.
- Among the selected regions, in the cold and severely cold regions with a large temperature diurnal range and low average temperature, the energy-saving efficiency was relatively high.
- For the tilted PV roof, this paper took 30° as the inclined angle, but the specific installation and the actual energy-saving effect should be determined after detailed analysis according to the local latitude and other conditions.
- The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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