scispace - formally typeset
Search or ask a question
Journal ArticleDOI

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)

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.

Did you find this useful? Give us your feedback

Citations
More filters
01 Jan 2016

1,633 citations

Journal ArticleDOI
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

Journal ArticleDOI
01 Sep 2021-Energy
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

Journal ArticleDOI
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
More filters
Journal ArticleDOI
TL;DR: In this article, the energy balance of photovoltaic (PV) cells is modelled based on climate variables, and it is found that the most precise fit to measured data is obtained by fitting the value of the forced convection coefficient for module convection.

482 citations


"A method for evaluating both shadin..." refers background in this paper

  • ...…PV module relative to the roof surface assumed to be30° αC Absorptivity of PV battery pack 0.95 (Wang et al., 2006) εC Emissivity of PV battery pack 0.84 (Jones and Underwood, 2001) εb Emissivity of TPT backsheet 0.893 (National Standard of PR China, 2016) αr Absorptivity of the exterior surface…...

    [...]

Posted Content
TL;DR: A new understanding of roof area distribution and potential PV outputs has an immense significance to energy policy formulation in Ontario and the methodology developed here is transferable in other regions to assist in solar PV deployment.
Abstract: Solar photovoltaic (PV) technology has matured to become a technically viable large-scale source of sustainable energy. Understanding the rooftop PV potential is critical for utility planning, accommodating grid capacity, deploying financing schemes and formulating future adaptive energy policies. This paper merges the capabilities of geographic information systems and object-based image recognition to determine the available rooftop area for PV deployment in an example large-scale region in south eastern Ontario. An innovative five-step procedure has been developed for estimating total rooftop PV potential which involves geographical division of the region; sampling using the Feature Analyst extraction software; extrapolation using roof area-population relationships; reduction for shading, other uses and orientation; and conversion to power and energy outputs. A relationship across the region was found between roof area and population of 70.0 m2/capita ± 6.2%. For this region with appropriate roof tops covered with commercial solar cells the potential PV peak power output is 5.74 GW (157% of the region’s peak power demands) and the potential annual energy production is 6909 Gwh (5% of Ontario’s total annual demand). This suggests that 30% of Ontario’s demand can be met with province-wide rooftop PV deployment. This new understanding of roof area distribution and potential PV outputs has an immense significance to energy policy formulation in Ontario and the methodology developed here is transferable in other regions to assist in solar PV deployment.

359 citations

Journal ArticleDOI
TL;DR: In this article, a critical discussion and a suitable tabulation is presented, on the basis of algebraic form of the coefficients and their dependence upon characteristic length and wind direction, in addition to wind speed.

337 citations


"A method for evaluating both shadin..." refers background in this paper

  • ...(Palyvos, 2008); IDI denotes the intensity of roof incident scattered radiation in the absence of shading in W/m2; VF and εr denotes the view factor and the roof surface emissivity, and they are both dimensionless; Fa, Fsky and Fgr denote the radiation angle coefficient between the outer roof…...

    [...]

Journal ArticleDOI
TL;DR: In this paper, a five-step procedure has been developed for estimating total rooftop PV potential which involves geographical division of the region; sampling using the Feature Analyst extraction software; extrapolation using roof area-population relationships; reduction for shading, other uses and orientation; and conversion to power and energy outputs.

327 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a new technique to compute the operating temperature of cells within building integrated photovoltaic modules using a one-dimensional transient heat transfer model, which can be used in conjunction with a calculation procedure to predict the module's temperature for various environmental conditions.
Abstract: A barrier to the widespread application of building integrated photovoltaics (BIPV) is the lack of validated predictive performance tools Architects and building owners need these tools in order to determine if the potential energy savings realized from building integrated photovoltaics justifies the additional capital expenditure The National Institute of Standards and Technology (NIST) seeks to provide high quality experimental data that can be used to develop and validate these predictive performance tools The temperature of a photovoltaic module affects its electrical output characteristics and efficiency Traditionally, the temperature of solar cells has been characterized using the nominal operating cell temperature (NOCT), which can be used in conjunction with a calculation procedure to predict the module's temperature for various environmental conditions The NOCT procedure provides a representative prediction of the cell temperature, specifically for the ubiquitous rack-mounted installation The procedure estimates the cell temperature based on the ambient temperature and the solar irradiance It makes the approximation that the overall heat loss coefficient is constant In other words, the temperature difference between the panel and the environment is linearly related to the heat flux on the panels (solar irradiance) The heat transfer characteristics of a rack-mounted PV module and a BIPV module can be quite different The manner in which the module is installed within the building envelope influences the cell's operating temperature Unlike rack-mounted modules, the two sides of the modules may be subjected to significantly different environmental conditions This paper presents a new technique to compute the operating temperature of cells within building integrated photovoltaic modules using a one-dimensional transient heat transfer model The resulting predictions are compared to measured BIPV cell temperatures for two single crystalline BIPV panels (one insulated panel and one uninsulated panel) Finally, the results are compared to predictions using the NOCT technique

145 citations


"A method for evaluating both shadin..." refers methods in this paper

  • ...Back panel temperature of PV panels denoted by Tb can be obtained from the empirical formula for the back temperature of PV modules in the Sandia electrical performance model developed by Sandia National Laboratory (Davis et al., 2001)....

    [...]