Photovoltaic Roof Research Articles

A Method for Assessing the Potential of Multifunctional Retrofitting of Rural Roofs Based on GF-2 Remote Sensing Imagery

Green roofs and photovoltaic (PV) roofs are important forms of roof retrofitting, and unused rural roofs provide favorable conditions for the development of green roofs and PV roofs. Here, this study proposes a new method for assessing the potential of multifunctional retrofitting of rural roofs. Firstly, rural roof types were classified into three categories based on GF-2 imagery: flat roofs, east–west pitched roofs, and north–south pitched roofs. The roof types were extracted based on the revised U-Net model, which aims to enhance the extracted features of the buildings and improve the perception of the buildings. Secondly, three types of retrofits—PV roofs, green roofs, and PV-green roofs—were designed taking into account the type, orientation, and area of the roofs. Finally, the potential electricity and carbon benefits of the different retrofit types of roofs were calculated separately, with the aim of realizing an assessment of the potential for roof retrofitting in the rural areas of Mentougou, Beijing. The results of the study showed that 35,407 (281.97 ha) roofs could be used for multifunctional retrofitting. If rural roofs are retrofitted with multifunctionality according to the methodology of this paper, they can absorb an additional 4.66 × 104 kg/yr of CO2 and increase biomass production by 0.99 × 104 kg/yr compared to retrofitting only PV roofs, and they can generate an additional 34.1 GWh/yr of electricity and reduce CO2 emissions by an additional 3.3 × 107 kg/yr compared to retrofitting to both PV roofs and green roofs. The assessment methodology of this study provides decision makers with data references on the multifunctional potential of rural rooftops for retrofitting, which can optimize the use of rural rooftops, and at the same time is important for promoting the energy transition in rural areas.

Integrated seismic and energetic rehabilitation of existing buildings based on the tuned mass damper concept

The preservation of the existing building heritage to guarantee structural integrity is a paramount concern. At the same time, energy rehabilitation to enhance existing buildings efficiency is a key issue. In recent years the scientific community is making efforts to explore integrated seismic and energy retrofitting techniques combining them into a single assessment also pointing to a sustainable design. The paper explores for the first time the implementation of novel integrated seismic and energetic rehabilitation techniques drawing upon the concept of tuned mass damper (TMD). The structural solutions proposed implement the TMD concept on the roof, disconnected and isolated from the substructure, by means of different approaches realizing a non-conventional TMD, a TMD with large mass ratio and a tuned mass damper inerter (TMDI). The seismic retrofit interventions are seamlessly integrated with suitable energy retrofit strategies exploiting the same element realizing a cool roof, a photovoltaic roof, a green roof. A straight methodology for the implementation and design of the integrated interventions and a new procedure to select the optimal intervention is proposed. The methodology is exemplified on a case study of a typical reinforced concrete building. The results show that the realization of a lightweight photovoltaic roof employing a TMDI represents the optimal intervention, minimizing simultaneously interstory drifts and building primary energy consumption. However, it is highlighted that a different calibration of the weights given to the seismic and energy retrofits can affect the optimal choice.

A novel uncertainty quantification method for electricity performance of building photovoltaic systems from multiple weather data sources

Distributed photovoltaic (PV) systems on buildings offer a promising solution for local renewable energy integration. As interest in sustainable energy grows, the demand for building PV systems is increasing. However, a significant challenge lies in accurately quantifying the uncertainty associated with building PV performance, particularly when considering multiple weather data sources. This study proposes a novel uncertainty quantification method to address this challenge. A case study of a building PV system with a PV wall and roof in Tianjin, China, is utilized to demonstrate the proposed method. Three types of weather data from different sources are considered: typical meteorological year data, multi-year historical data, and climate change projections. Uncertainty is quantified using a weighted-mean approach, incorporating weights based on recency, period, and accuracy of the data sources. Results indicate that the proposed method effectively integrates uncertainties from various data sources, providing reliable long-term energy yield estimates for PV systems. The variation coefficient of annual yield for the PV wall and roof system across ten typical meteorological year files is approximately 10 %. This study contributes to a comprehensive understanding of uncertainty in building PV performance, enabling informed decision-making in sustainable building design and energy management.

Correction: Ebner et al. Photovoltaic Roofing for Motorways and Other High-Ranking Road Networks: Technical Feasibility, Yield Estimation, and Final Demonstrator. Energies 2024, 17, 3991

In the published publication [...]

منازل تولد الطاقة المتجددة كحل مستدام لتلبية احتياجات الطاقة المنزلية في ليبيا

This study provides an overview of surplus energy-generating homes for integration with the public electricity grid and its potential for spatial development in Libya. With a special focus on the idea of a surplus energy-generating home, in addition to the study, the basic components of a solar home system are solar panels and the conversion of building glass panels into solar power generators. The performance of housing and its occupants, especially the sustainable development aspects. Then, research and present the most important proposals for the installation of home photovoltaic roofs that generate surplus energy as a guaranteed way to meet the home's energy needs, achieve economic and environmental gains for its occupants, and contribute to sustainable development. Keywords: Solar system, grid integration, sustainable development, home photovoltaic roofs, Smart homes.

The Role of Solar Photovoltaic Roofs in Energy-Saving Buildings: Research Progress and Future Development Trends

The Role of Solar Photovoltaic Roofs in Energy-Saving Buildings: Research Progress and Future Development Trends

Using the Taguchi Method and Grey Relational Analysis to Optimize Ventilation Systems for Rural Outdoor Toilets in the Post-Pandemic Era

This study addresses the issue of poor air quality and thermal comfort in rural outdoor toilets by proposing a ventilation system powered by a building-applied photovoltaic (BAPV) roof. A numerical model is established and validated through comparison with the literature and experimental data. Based on a consensus, four influential variables, namely, inlet position, outlet height, supply air temperature, and ventilation rate, are selected for optimization to achieve multiple objectives: reduction in ammonia concentration, a predicted mean vote (PMV) value of 0, minimization of age of air, and energy consumption. The present study represents a pioneering effort in integrating the Taguchi method, computational fluid dynamics (CFD), and grey relational analysis to concurrently optimize the influential variables for outdoor toilet ventilation systems through design and simulation. The results indicate that all four variables exhibit nearly equal importance. Ventilation rate demonstrates a dominant effect on ammonia concentration and significantly impacts the age of air and energy consumption, while supply air temperature noticeably influences PMV. The optimal scheme features an inlet at center top position, an outlet height of 0.2 m, a supply air temperature of 12 °C and a ventilation rate of 20 times/h. This scheme improves ammonia concentration by 18.9%, PMV by 6.8%, and age of air by 30.0% at a height of 0.5 m, while achieving respective improvements by 18.9%, 5.5%, and 22.2% at a height of 1.5 m. The BAPV roof system generates an annual electricity output of 582.02 kWh, which covers the energy consumption of 358.1 kWh for toilet ventilation, achieving self-sufficiency. This study aims to develop a zero-carbon solution for outdoor toilets that provides a safe, comfortable, and sanitary environment.

Photovoltaic Roofing for Motorways and Other High-Ranking Road Networks: Technical Feasibility, Yield Estimation, and Final Demonstrator

As renewable energies need to be extended massively, new concepts are necessary to prevent land conflicts with other uses. Such concepts should have a high generality to offer a swift expansion of renewables anywhere. Within the project, the Photovoltaic Road Roofing Concept (PV-SÜD), a concept for the roofing of roadways with solar panels, was investigated. Its effects on the road infrastructure were analyzed, and a demonstrator was built. The technical boundary conditions and requirements resulting from the specific application type were determined regarding the photovoltaic technology, the possible energy generation, and the supporting structure. The study was completed for a technical solution of 10 m length, 17 m width, and 6.8 m height, with the option of a pent roof (highways running east–west) or gable roofs (highways running north–south). The main target aim was to investigate the potential for widespread use at any site, in contrast to previous studies which mainly aimed at a singular site or demonstrator project. The final solution can support a 38.5 kWp photovoltaic system with a specific annual yield of between 37.5 MWh and 44.0 MWh. The yield variation in sites in Austria and Germany was 14.7% and 17.9%, respectively. One demonstrator roofing was realized as a steel-frame construction with active glass–glass photovoltaic technology at a highway in Hegau (GE).

CO2 emission mitigation of a hybrid photovoltaic and cogeneration system in computer hardware manufacturing industry: A case study in Thailand

Abstract In the wake of COP26 and the growing urgency of addressing climate change, achieving carbon neutrality by 2050 has become a central global objective. This imperative extends to industries like computer hardware manufacturing, which are now actively pursuing decarbonization strategies through the strategic adoption of renewable energy sources and energy efficiency enhancements. This research paper assessed the CO2 emission mitigation potential of a hybrid system of photovoltaic (PV) roof and cogeneration where a large factory of computer hardware manufacturing in tropical Thailand was selected as a study site. On one hand, a one-Megawatt photovoltaic system was installed over the roof of the production building to generate electricity from solar radiation to serve the building. On the other hand, a twenty-four-Megawatt cogeneration system of gas engines as the prime mover was used to supply power to meet the building’s electricity demand. Waste heat from the gas engine was used by the absorption chiller to generate chilled water for cooling inside the building. Based on the system equipment specifications, the annual simulation using Thailand’s solar radiation showed that the installed photovoltaic system could generate electricity of 1,412.4 MWhelec/year while the implementation of the absorption chillers for cooling helped to reduce the electrical energy consumed by the traditional electric chiller by 10,211.4 MWhelec/year. In our study case where the CO2 emission of the grid power was 0.4758 kgCO2/kWhelec in the year 2022 and was reduced to 0.350 kgCO2/kWhelec in the year 2050, the total CO2 emission mitigation from the hybrid photovoltaic and cogeneration system with the genset efficiency of 50% and the waste heat recovery of 60% could reduce approximately 207,388.5TonCO2 for over 20 years as compared to the scenario where the grid electricity alone powered the building. These findings underscored the critical role of the proposed hybrid system in addressing the climate crisis and exemplified how the industry could make meaningful strides toward more environmental sustainability.

5. Development of a method for the evaluation of the impact of photovoltaic roof shelters on the outdoor run of free-range poultry farming

5. Development of a method for the evaluation of the impact of photovoltaic roof shelters on the outdoor run of free-range poultry farming

PromptNet: Prompt Learning for Roof Photovoltaic Potential Assessment

An increasing number of works have been proposed to use remote sensing images to assess the potential for rooftop Photovoltaic (PV) energy development in buildings. However, most methods focus mainly on the remote sensing images themselves, ignoring the key prior information of building type. Thus most works with Deeplabv3+ as backbone present suboptimal performance. To overcome this challenge, we propose a novel approach PromptNet that embeds the building types as prior knowledge and feed it into prompt learning for predict roof PV energy Potential. Specifically, a pre-trained semantic segmentation network, Deeplabv3+, is first constructed to detect potential building rooftops from remote sensing images. Then, the buildings are categorized into five types based on their functions, including government buildings, public buildings, industrial and commercial factories, agricultural housing, and other building types. Finally, by using prompt learning, the prior knowledge of buildings is established and associated with the rooftops that are suitable for PV energy development. This is embedded into a deep learning network, filtering out unsuitable rooftops, and significantly improving the accuracy of rooftop PV energy development. Comprehensive experiments show that the proposed method achieves 81.18% accuracy and 76.90% IOU in predicting the potential for rooftop PV energy, a 10.97% improvement in IoU compared to the backbone without prior knowledge.

Experimental and numerical study of thermal and electrical potential of BIPV/T collector in the form of air-cooled photovoltaic roof tile

Among renewable energy sources, Building-Integrated Photovoltaic/Thermal (BIPV/T) systems are gaining increasing interest. To improve their economic competitiveness, technologies that increase their efficiency are searched for. The paper is devoted to evaluating the impact of various air-cooling configurations on the thermal and electrical performance of a photovoltaic roof tile. A numerical model of the own experimental system was developed in the ANSYS Fluent software for a wide range of input variables. The original approach based on the SST k-ω turbulence model, Discrete Ordinates radiation model, and the use of Solar Load module were proposed. Such a numerical model allows representation of semi-transparent layers and variable solar irradiance, which is a unique realization of real system modelling. Numerous analyses conducted indicate a higher heat recovery potential for an airflow duct with a height of 25 mm for all configurations analysed. The highest value of recovered heat flux was approximately 330 W/m2 under conditions of a volumetric air flow rate of 7.5 m3/h and solar irradiance equal to 900 W/m2. Good agreement of the results of the multivariant CFD simulations with new experimental ones was confirmed. Insight into the flow phenomena behind the achieved thermal results supplemented the knowledge. The highest electrical efficiency obtained experimentally was 5.76 % for a channel with a height of 50 mm, volumetric flow rate equal to 7.5 m3/h and solar irradiance equal to 600 W/m2. The presented methodology and the results obtained can be useful in research devoted to optimising BIPV/T air-based cooling systems, which will then be tested in-situ. Moreover, new experimental data collection can be used for the verification of numerical models.

Experimental and numerical study to optimize building integrated photovoltaic (BIPV) roof structure

The study addresses the issue of heat dissipation in Building Integrated Photovoltaic (BIPV) roofs by proposing a novel PV module and establishing its testbed in Beijing, China, which is extended to more structures by the validated numerical model. The validation reveals MBD (mean bias difference）values of 10.24% for electricity production and 9.32% for temperature, accompanied by corresponding RMSD (root mean square difference) values of 23.97% and 10.46%, respectively. Taguchi method and Computational Fluid Dynamics (CFD) numerical simulation were employed to design and simulate orthogonal schemes, optimizing BIPV roof structure for the first time by considering three factors: air gap thickness, PV panel spacing and heating power. The results indicate that the air gap thickness impacts most on PV panel temperature, followed by meteorological parameters and PV panel spacing. The optimal BIPV roof structure, featured an air gap of 68 mm and a PV panel spacing of 30 mm, exhibits a 25.35% reduction in PV panel temperature, an 8.78% increase in signal-to-noise (S/N) ratio and a 2.49% growth in electricity production compared to the performance of the intermediate level scheme.

Numerical research on air-based cooling photovoltaic roof

As a new type of building material for plants, photovoltaic roof building materials can be used as roofs of ordinary plants to reduce damage caused by secondary construction to the roofs, and can also absorb and utilize solar radiation to make full use of renewable energy. This article combines photovoltaic modules with air channels to form building material structures with ventilation ducts, establishes physical and mathematical models for photovoltaic roofs in three different inlet modes, and studies the flow and heat transfer characteristics inside air cooling integrated photovoltaic roofs. The simulation results show that the staggered-overlap-joint waterproof double-inlet photovoltaic roof can prevent rain and snow infiltration, and meanwhile, has a cooling effect on the PV panels significantly better than that of the traditional single-inlet air cooling system and the ordinary parallel double-inlet system, and its temperature difference between the inner and outer surfaces of the PV panels is increased by 19.88% compared to the traditional single-inlet air cooling system and by 15.12% compared to the parallel double-inlet system at the maximum. When the included angle between the PV panels of the staggered-overlap-joint waterproof double-inlet photovoltaic roof and the roof is 3°, the change in average temperature difference between the inner and outer surfaces of the PV panels is maximum, which is increased by 3.88% compared with that at 2°. The thickness of the air channel has small influences on the temperature change inside the air channel, the temperature difference between the inner and outer surfaces of the PV panels, and the outlet temperature. When the thickness increases from 50 mm to 200 mm, the change in outlet temperature does not exceed 0.3 K, but the increase in thickness of air layers increases the airflow velocity, which helps to take away more heat.

Assessing multifunctional retrofit potential of urban roof areas and evaluating the power and carbon benefits under efficient retrofit scenarios

Green roof installations and photovoltaic (PV) systems are widely employed roof retrofits that aid cities in mitigating climate change impacts, while avoiding the need for increased land utilization. By integrating PV systems with vegetation on urban roofs, a photovoltaic-green (PV-Green) system can be achieved for multifunctional use of the roof space, thereby simultaneously achieving PV and greening benefits. However, current research solely based on one retrofit type cannot meet the requirement for assessing the multifunctional retrofit potential of urban roofs. In this study, an assessment method is proposed to identify and quantify the multiple retrofit potential of urban roofs by integrating roof attributes (slope, orientation, and area), roof type (gable or flat), solar attributes (radiation and irradiation duration), and biogeochemical simulation. Moreover, three roof retrofit scenarios, Scenario 1 (S1): maximization of PV-Green roofs, Scenario 2 (S2): maximization of PV economic benefits, and Scenario 3 (S3): maximization of public subjective well-being through roof greening, were designed to allocate the use of urban roof spaces and evaluate their respective potential power and carbon benefits at the city scale. Using Shanghai's downtown as an example, the results showed that 85,722 roofs (or 7310.86 ha) were available for multifunctional use. S1 revealed that applying PV-Green roofs can increase the additional green biomass by 0.74 × 107 kg C/yr compared to only installing PV roofs. Moreover, S1 produced the highest power output of 2.31 × 1010 kWh/yr to meet 15.4% of Shanghai's electricity demand. S2 identified 609 flat roofs and 70,527 gable roofs that were uneconomical for PV system installation. This indicated that the solar radiation received by most gable roofs was insufficient to cover the installation cost. S3 offered a biomass production of 1.48 × 107 kg C/yr and increased carbon stocks in Shanghai by 0.87%. This assessment method provides urban planners and policymakers with an analytical tool to optimize the use of urban roof spaces, thereby enhancing urban livability and sustainability.

Actuality and technology prospect of using perovskite quantum dot solar cells as the photovoltaic roof

PV architecture is the main form of low-carbon architecture, it has great significance for realizing zero-energy buildings (ZEB) The photovoltaic (PV) roofing project is an important form of PV architecture. The materials currently on the market such as silicon and copper indium gallium selenide (CIGS) are unable to meet both the cost and aesthetic requirements of architectural design. So, a new technical scheme has been emphasized to eliminate the color inconsistency between the PV roofing and building and costing by using perovskite quantum dots solar cells（PQDSC） in PV facilities. The technical requirements of PV roofing are sorted out from the architectural perspective based on general standards. PQDSC has the potential to meet regulatory requirements due to its flexibility, light weight color transparency. Then solutions to the underlying technical problems such as the structural design of PV building components, PV basic materials, and color adjustment of PV modules are analyzed and summarized. The potential of PQDSC for applications in PV roofing projects has been largely prospected due to the promising directions they reveal for further research.

Economic and life cycle cost analysis of building-integrated photovoltaic system for composite climatic conditions.

An insulated building-integrated photovoltaic (PV) roof prototype is designed, developed, and experimentally monitored for the composite climatic conditions in the current work. The prototype is monitored based on hourly indoor room temperature, relative humidity, discomfort index, decrement factor time lag, and power generation. To validate the results, a heat conduction equation was developed and simulated considering actual lower income group (LIG) building size and materials. Second-order polynomial equations were derived from simulation results to optimize insulation thickness. Additionally, the economic analysis of the insulated building-integrated Photovoltaic (BIPV) roof was analyzed and compared to the reinforced concrete cement (RCC) roof. The results reveal that insulated BIPV roofs outperform the RCC roof, reducing indoor temperatures by 3.34 ℃ to 1.37 ℃ within an optimum thickness range of 0.0838-0.1056m. A time lag of 1h and a significant reduction in decrement factor up to 0.29 are achieved. The average discomfort index of the proposed roof during sunshine hours was found to be between 23 and 26.5. The insulated BIPV roofs with levelized cost of electricity (LCOE) of the 3.38 Rs/kWh gave a payback period of 6.32years and a higher internal rate of return of 29.4 compared to RCC roof. The current study increases the feasibility of PV modules to be used as building material.

Roofing systems and energy efficiency in low-rise buildings: A comparative study across India’s diverse climates

The building envelope is the interface between the external atmospheric conditions and the indoor environment. It contributes to approximately 60%–70% of the heating and cooling load. The building envelope constitutes walls, fenestrations, and roofs from which thermal transfer from the roof is significantly very high compared to walls in low-rise buildings.This research paper aims to provide recommendations for energy-efficient roof design considering roof form, material, and external coating suitable for various climate conditions of India. The paper’s methodology consists of a literature review of related research papers, learnings from the roofing system of energy-efficient building case studies, and all possible energy-efficient roofing systems that would be simulated for energy efficiency and thermal comfort in five climate types of India. The expected outcome of this paper would be in the form of recommendations for roofing systems in different climate type and their potential for energy saving from the highest to the lowest. This research would be done in three stages viz, Step-1: Literature Review and case study of best practices: A review of the related literature and best practices examples would be done to formulate the maximum possible cases for the simulation. Step-2: The roofing systems, including building form, material (Thermal and insulation), and finishes (reflectance), would be simulated one by one for various climate types of India (composite, hot & dry, warm and humid, moderate and cold) to optimize energy efficiency and payback period. Step-3: Special roof types like Green roofs, cool roofs, Photovoltaic roofs, roof ponds, and the like are simulated and compared for their effectiveness in selected climate types. Based on the literature review, simulation results, and analysis, the recommendations are framed for energy-efficient roofing systems in the selected climate type with respect to heat transfer through the roof and thermal comfort.

Effect of Simulated Photovoltaic Roofs on the Yield and Nitrate Content of Pak Choi and Rape

Integrating solar modules into agricultural production constitutes a novel type of agricultural industry. We evaluated the effect of setting opaque plastic solar modules on greenhouse roofs on the crop growth inside greenhouse. The opaque plastic agricultural films simulating the material of solar modules and the greenhouse roofs covered with these films were used, and the yield and nitrate content of pak choi (Brassica chinensis ‘Bekamaru’) and rape (Brassica napus ‘Dragon’) under these films were measured. The results indicated that the yield of pak choi did not change considerably by a simulated photovoltaic (SPV) roof with a shading rate of 38% compared with an uncovered plastic (PL) roof. However, during the first and second planting periods, the yield of rape under the PL roof substantially exceeded that under the SPV roof by 31% and 34%, respectively, indicating that the effect of shading on the yield of rape was greater than that on the yield of pak choi. In addition, the appearance of pak choi and rape also changed under the SPV roof, such as fewer leaves, lower chlorophyll content, and larger specific leaf areas. Nevertheless, the nitrate content of crops grown under the SPV roof exceeded that of crops grown under the PL roof. In conclusion, based on the expression of yield and growth of crops, pak choi is suitable for cultivation in greenhouses that are equipped with photovoltaic systems. However, to prevent plants from accumulating excessive nitrate, attention must be focused on the amount and frequency of nitrogen fertilizers application.

Shading effect and energy-saving potential of rooftop photovoltaic on the top-floor room

Rooftop photovoltaic panels can serve as external shading devices on buildings, effectively reducing indoor heat gain caused by sunlight. This paper uses a numerical model to analyze rooftop photovoltaic panels' thermal conduction, convection, and radiation in hot summer areas as shading devices. The researcher builds an experimental platform to verify the model, exploring the potential for energy savings of photovoltaic rooftop units in the Wuhan area. The results show that after installing photovoltaic panels, the delay performance of the roof increases by 0.5 h, the roof heat flux is reduced by 41.7%, the peak temperature of the roof is reduced by 22.9 °C, and the daily heat gain is reduced by 74.84%. Finally, this paper discusses the impact of high-reflectance and low-reflectance roofs on the shading effect. The study finds that low-reflectance roofs are more energy-efficient in the hot summer, as high-reflectance roofs lead to a 10.8% increase in indoor heat gain when the photovoltaic panel is installed. Finally, a quantitative method for evaluating the comprehensive potential for energy savings is proposed, considering the electricity generation gain of photovoltaic panels and the comprehensive energy-saving efficiency of photovoltaic roofs, which generates a total potential for energy savings rate of 61.06%. The model presented in this paper provides theoretical guidance for analyzing the comprehensive energy-saving effects of photovoltaic rooftop systems and reveals the potential for energy savings of rooftop photovoltaic panels as external shading devices.