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| Fig. 1: Photovoltaic wall near Barcelona, Spain. (Source: Wikimedia Commons) |
Resident and industry-centralized cities face increasing energy demands and rising environmental heat. Fig.1 shows the application of building-integrated photovoltaics(BIPV) in Spain. BIPVs have been widely found in America, Canada, Europe, etc. They consider BIPVs as a promising way to efficiently reduce indoor heat and thus electricity usage. Architecture is designed to enhance building performance while reducing carbon footprints. Among the most promising solutions are green roofs and BIPV, two technologies that transform underutilized building surfaces into functional systems for insulation, cooling, and renewable energy generation. Studies have shown that green roofs can significantly reduce heat flux and rooftop temperatures, while BIPV systems can generate substantial on-site renewable electricity while replacing conventional building materials. [1,2] When used together, these approaches form a synergistic "biosolar" configuration in which vegetation helps regulate rooftop temperatures and improves photovoltaic efficiency - a relationship supported by findings that cooler microclimates can enhance PV output. [3] This raises an important question: How can buildings effectively integrate green roofs and BIPV to maximize energy savings while maintaining economic viability and long-term practicality?
Green roofs contribute to substantial energy savings by moderating rooftop temperatures and reducing heat flux through the building envelope, thereby decreasing cooling loads. In parallel, building-integrated photovoltaics (BIPV) have been widely explored as an additional strategy for improving building energy performance, particularly in regions with strong solar resources such as California. For example, Joseph et al. evaluated the energy performance of a photovoltaic double-skin façade (PV-DSF). [3] They demonstrated an annual electricity generation of 65 kWh per square meter, a 50% reduction in lighting electricity use during winter, and a 15% net annual energy savings compared to a baseline façade. BIPV technologies are commercially categorized into foil products, tile products, solar glazing products, and module products. Among these, module products function similarly to conventional photovoltaic systems and can be mounted alongside various roofing materials. [4,5] In this work, the focus is placed on solar glazing, which is typically integrated into façades, roofs, or window systems and offers both functional and aesthetic advantages. Semitransparent BIPV windows, in particular, have been studied in commercial buildings across tropical regions, where they were shown to reduce total heating and ventilation energy consumption by approximately 30% compared with conventional clear glazing systems. [3] Looking ahead, advances in emerging photovoltaic technologies such as third-generation organic-based systems, including dye-sensitized and TiO₂ solar cellsare expected to further improve the efficiency, transparency, and cost-effectiveness of semitransparent BIPV. Continued technological innovation, along with growing stakeholder awareness and market adoption, will be essential in driving the broader application of these systems in sustainable building design.
The combined use of green roofs and building-integrated photovoltaics (BIPV) represents a powerful strategy for enhancing building energy performance while contributing to broader urban sustainability goals. Evidence from recent studies shows that green roofs significantly reduce rooftop temperatures and cooling loads, while BIPV systems can supply a meaningful portion of on-site renewable electricity and displace conventional building materials. When integrated as a biosolar system, these technologies offer synergistic benefits, including a measurable increase in photovoltaic efficiency due to the cooling effect of rooftop vegetation. Despite these advantages, successful implementation depends on thoughtful design considerations such as structural capacity, system configuration, climate conditions, and maintenance requirements as well as careful evaluation of economic feasibility. As cities continue to confront climate change and rising energy demands, understanding how to optimize the integration of green roofs and BIPV becomes increasingly essential. Ultimately, this dual-technology approach not only advances building-level energy efficiency but also contributes to resilient, livable urban environments, underscoring the need for further research and practical frameworks to guide its adoption.
© Wen-Shin Lu. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] U. Berardi, "The Outdoor Microclimate Benefits and Energy Saving Resulting From Green Roofs Retrofits," Energy Build. 121, 217 (2016).
[2] P. B. Jelle, C. Breivik, and H. D. Røkenes, "Building Integrated Photovoltaic Products: A State-of-the-Art Review and Future Research Opportunities," Sol. Energy Mater. Sol. Cells 100, 69 (2012).
[3] B. Joseph, T. Pogrebnaya, and B. Kichonge, "Semitransparent Building-Integrated Photovoltaic: Review on Energy Performance, Challenges, and Future Potential," Int. J. Photoenergy 2019, 5214150 (2019).
[4] Y. T. Chae et al., "Building Energy Performance Evaluation of Building Integrated Photovoltaic (BIPV) Window With Semi-Transparent Solar Cells," Appl. Energy 129, 217 (2014).
[5] J. Peng et al., "Numerical Investigation of the Energy Saving Potential of a Semi-Transparent Photovoltaic Double-Skin Façade in a Cool-Summer Mediterranean Climate," Appl. Energy 165, 345356 (2016).
