Powering Entire Cities through Urban Photovoltaics

Significance 

Buildings generate nearly 40% of annual global CO2 emissions. Of those total emissions, building operations are responsible for 28% annually, while building materials and construction are responsible for an additional 11% annually. Without widespread building decarbonization across the globe, these buildings will still be emitting CO2 emissions for decades to come and we will not achieve the Paris Agreement’s 1.5°C target. Achieving zero emissions from the existing buildings will require leveraging building intervention points to accelerate the rate of energy upgrades by increasing energy efficiency, eliminating on-site fossil fuels, and generating 100% renewable energy. While solar photovoltaic (PV) is expected to play a vital role in this pursuit, PV deployment in highly urbanized environments remains scarce due to rooftop and ground space limitations. To this end, building-integrated PV (BIPV), which involves integrating PV modules into walls, roofs and surfaces of the buildings, has been deemed a prospective technology.

Compared with the conventional building-applied PV (BAPV) systems, BIPV is economically feasible because it replaces some parts of the building and their initial cost can be offset by reducing the cost of these parts. Thus, BIPV is forecasted to grow in the next decade. The exponential growth of PV witnessed in recent years can be mainly attributed to the rapid development of highly efficient and cost-effective crystalline silicon PVs. Extensive studies, mainly through simulation methods, have been carried out to estimate the PV potential of buildings. Recently, these studies have been extended to simulate the solar and PV potential of urban buildings, including the building rooftops, surfaces and facade areas.

Generally, the PV potential of urban environments is dependent on several factors such as the perceived energy efficiency of the buildings, thermal losses/gains, daylight and solar availability and several density factors like site coverage, population and building density and plot ratio. While remarkable progress in understanding the PV potential of urban environments has been made, most studies focus on the potential of building rooftops and walls. Thus, the overall PV potential of urban environments is yet to be fully explored. Moreover, there is a need to inform the various stakeholders of the various aspects and benefits of solar energy generation in urban environments.

To this note, a team of Monash University researchers in Australia: Dr. Maria Panagiotidou, Professor Kais Hamza, Professor Jacek Jasieniak and Dr. Jin Zhou in collaboration with Professor Miguel Brito from Universidade de Lisboa analyzed the solar energy harvesting potential of BIPV integrated as walls, rooftops and windows taking into account different spatial scale resolutions ranging from the city to the building. Melbourne City in Australia was used as a complementary case study. The key objectives were to establish the relationship between the urban morphology and the PV potential of the buildings and to identify the urban characteristics associated with high semi-transparent PV (ST-PV) window potential. The work is currently published in the journal, Solar Energy.

The research team showed that the rooftops accounted for the largest share of the city’s PV potential. Overall, the PV potential of the urban environment can cover over 70% of its energy needs. BAPV roofs played a dominant role, contributing 88% of the total PV potential, while BIPV walls and ST-PV windows supply 8% and 4%, respectively. Meanwhile, for predominantly glass-based individual high-rise buildings within dense urban areas, the ST-PV windows could produce up to 100% of the PV potential. Notably, the more northly sun and reduced daytime in winter periods was found to result in drastic reductions in relative PV productions during these periods for BAPV rooftop compared to BIPV windows and ST-PV windows, which allowed more stable yearly production. These factors therefore suggest that a broadened adoption of these latter technologies will effectively optimize PV generation potential in cities.

In summary, the researchers reported the PV potential in urban environment consisting of integrated PV technologies across the walls, windows and roofs of urban buildings. The total PV potential of the urban environment was estimated based on the estimations of the urban scale ST-PV window potential and emerging BIPV wall and BAPV rooftop potential. The presented framework would enable cities and relevant stakeholders to effectively plan for the large-scale deployment of solar energy generation. In a statement to Advances in Engineering, Professor Jacek Jasieniak, the lead and corresponding author explained the global deployment of highly-efficient BIPV and ST-PV windows in dense urban areas would play a critical role in reducing carbon footprint. He said that “while rooftop solar remains the low-hanging fruit for maximizing PV production within dense urban environments, the growing technological maturity of BIPV walls and ST-PV windows make these highly attractive emerging markets”.

Powering Entire Cities through Urban Photovoltaics - Advances in Engineering Powering Entire Cities through Urban Photovoltaics - Advances in Engineering

Reference

Panagiotidou, M., Brito, M., Hamza, K., Jasieniak, J., & Zhou, J. (2021). Prospects of photovoltaic rooftops, walls and windows at a city to building scaleSolar Energy, 230, 675-687.

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