A method for evaluating both shading and power generation effects of rooftop solar PV panels for different climate zones of China
TL;DR: In this article, three types of PV rooftops, namely, horizontally-mounted overhead PV rooftop, tilted overhead PV roof, 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.
About: This article is published in Solar Energy.The article was published on 2020-07-15 and is currently open access. It has received 33 citations till now. The article focuses on the topics: Photovoltaic system & Solar gain.
Summary (2 min read)
Jump to: [1. Introduction] – [3. Experimental results and model validation] – [4. Analysis and discussions of overall energy-saving performance] and [5. Conclusions]
1. Introduction
- 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.
5. Conclusions
- 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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Citations
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TL;DR: In this article, a review of various factors that affect the design and performance of building-attached and building integrated photovoltaic (BIPV) system applications is presented.
Abstract: Integration of photovoltaic (PV) technologies with building envelopes started in the early 1990 to meet the building energy demand and shave the peak electrical load. The PV technologies can be either attached or integrated with the envelopes termed as building-attached (BA)/building-integrated (BI) PV system. The BAPV/BIPV system applications are categorized under the building envelope roof and facades as PV-roof, PV-skin facade, PV-Trombe wall, PV claddings, and louvers. This review covers various factors that affect the design and performance of the BAPV/BIPV system applications. The factors identified are air gap, ventilation rate, a tilt angle of PV shading devices, adjacent shading, semitransparent PV (STPV) glazing design, cell coverage ratio (CCR), transmittance, window to wall ratio (WWR), and glazing orientation. Furthermore, the results of the possible factors are compared to building locations. This review article will be beneficial for researchers in designing the BAPV/BIPV system and provides future research possibilities.
35 citations
03 Aug 2010
TL;DR: In this paper, the effect of rooftop PV systems on the building roof and indoor energy balance as well as their economic impacts on building HVAC costs have been investigated, and the authors report extensive measurements of a building containing a flush mount and a tilted solar PV array.
Abstract: Building Heating, Ventilation and Air Conditioning (HVAC) is a major contributor to urban energy use. In single story buildings with large surface area such as warehouses most of the heat enters through the roof. A rooftop modification that has not been examined experimentally is solar photovoltaic (PV) arrays. In California alone, several GW in residential and commercial rooftop PV are approved or in the planning stages. With the PV solar conversion efficiency ranging from 5-20% and a typical installed PV solar reflectance of 16-27%, 53-79% of the solar energy heats the panel. Most of this heat is then either transferred to the atmosphere or the building underneath. Consequently solar PV has indirect effects on roof heat transfer. The effect of rooftop PV systems on the building roof and indoor energy balance as well as their economic impacts on building HVAC costs have not been investigated. Roof calculator models currently do not account for rooftop modifications such as PV arrays. In this study, we report extensive measurements of a building containing a flush mount and a tilted solar PV array as well as exposed reference roof. Exterior air and surface temperature, wind speed, and solar radiation were measured and thermal infrared (TIR) images of the interior ceiling were taken. We found that in daytime the ceiling surface temperature under the PV arrays was significantly cooler than under the exposed roof. The maximum difference of 2.5 C was observed at around 1800h, close to typical time of peak energy demand. Conversely at night, the ceiling temperature under the PV arrays was warmer, especially for the array mounted flat onto the roof. A one dimensional conductive heat flux model was used to calculate the temperature profile through the roof. The heat flux into the bottom layer was used as an estimate of the heat flux into the building. The mean daytime heat flux (1200-2000 PST) under the exposed roof in the model was 14.0 Watts per square meter larger than under the tilted PV array. The maximum downward heat flux was 18.7 Watts per square meters for the exposed roof and 7.0 Watts per square meters under the tilted PV array, a 63% reduction due to the PV array. This study is unique as the impact of tilted and flush PV arrays could be compared against a typical exposed roof at the same roof for a commercial uninhabited building with exposed ceiling and consisting only of the building envelope. Our results indicate a more comfortable indoor environment in PV covered buildings without HVAC both in hotter and cooler seasons.
23 citations
TL;DR: In this paper, the authors presented a technical, economic, and environmental evaluation of a residential building powered by hybrid intermittent generation systems in a mild humid subtropical climate zone in China.
21 citations
TL;DR: In this article, the authors proposed a novel technique to prevent the reverse breakdown and mitigate the hot spot temperature of the PV cells under partial shading by reducing reverse current through automated reconfiguration of PV array.
20 citations
References
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TL;DR: In this paper, a comprehensive energy efficiency model was proposed to analyze integrated contribution of shading and photovoltaics performance, which indicated that heat gain and cooling load of PV roof were attenuated while heating load increasing.
25 citations
TL;DR: It has been shown by many researchers that over a long term there has been a slow but steady rise of ambient temperature within the Indian sub-continent due to an increased economic prosperity as discussed by the authors.
Abstract: It has been shown by many researchers that over a long term there has been a slow but steady rise of ambient temperature within the Indian sub-continent. Due to an increased economic prosperity the...
23 citations
TL;DR: In this paper, an experimental study and a numerical model of the thermal behavior of a building whose roof is equipped with photovoltaic panels (PV panels) are presented to determine both the temperature field of the building and the electric production of the PV array.
21 citations
"A method for evaluating both shadin..." refers background in this paper
...Bigot et al. (2009) analyzed the influence of PV roof panels on the heating load of a roof in a humid tropical climate conditions and found that the heating load of the PV roof was reduced by 51% compared with that of a non-PV roof....
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TL;DR: In this paper, the authors used the TRNSYS simulation engine to investigate the shading and cooling effect of roof-added photovoltaics (PV) and showed that PV panels have a high impact on the roof surface temperature between shaded and exposed parts of the roof during the summer time.
Abstract: In this study, the TRNSYS simulation engine was used to investigate the shading and cooling effect of roof-added photovoltaics (PV). The local weather conditions were introduced in the data reader component. The sol-air effective temperatures were modeled in the roof–air boundary layer, while a single-zone model was used for the heat transfer calculation, both in bared and PV-shaded roof. The simulation was validated by experimental data of a PV installation at the roof of the Department of Environmental & Natural Resources Management. The simulation results show that PV panels have a high impact on the roof surface temperature between shaded and exposed parts of the roof during the summer time. Heat transfer simulation with or without roof-integrated PV shadings revealed the factors influencing cooling loads of a building during the year. The roof-added PV can passively reduce the daily rooftop cooling energy and peak load during the hot summer days in addition to electricity production.
15 citations
Dissertation•
01 Jan 2014
TL;DR: This document summarizes current capabilities, research and operational priorities, and plans for further studies that were established at the 2015 USGS workshop on quantitative hazard assessments of earthquake-triggered landsliding and liquefaction.
Abstract: ............................................................................................................................. xiv
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