A recent study reveals that widespread installation of rooftop photovoltaic solar panels (RPVSPs) could cause daytime temperatures to rise while lowering them at night in urban areas.
The research, led by Dr Ansar Khan from the University of Calcutta and co-authored by Scientia Professor Mattheos Santamouris from UNSW Sydney, employed mesoscale simulations to examine the impact of RPVSPs in cities.
Published in Nature Cities, the study highlights the potential daytime temperature increase of up to 1.5°C during peak summer periods with full rooftop solar panel coverage, while night time temperatures could decrease by as much as 0.6°C.
These results underscore the importance of understanding the complex effects of solar panels when implemented on a large scale in cities.
The research team, which modelled the impact in Kolkata, India, also conducted sensitivity studies in four other cities—Sydney, Austin, Athens and Brussels—to compare results.
They observed a linear relationship between the temperature rise and the percentage of rooftops covered with solar panels.
The findings have raised concerns about the heat generated by photovoltaic panels, particularly in urban environments.
"When solar panels are installed on roofs, they absorb significant solar energy, generating heat in the process," explained Professor Santamouris, who is also the Anita Lawrence Chair in High-Performance Architecture at UNSW Arts, Design & Architecture.
"During peak summer periods, rooftop panels can become as hot as 70°C, contributing to increased daytime temperatures," Professor Santamouris said.
However, the study also reveals that solar panels offer a cooling effect during the night, thanks to their capacity to transfer heat through radiation. This is particularly beneficial as night-time temperatures are expected to increase significantly due to global warming.
The research, which spanned from 2021 to 2023, also indicated that RPVSPs could reduce pollutant concentrations by increasing wind speeds and diluting pollutants. This is particularly significant for cities like Kolkata, where pollution is a critical issue.
Despite the potential drawbacks of increased daytime temperatures, the study does not discourage the use of rooftop solar panels. Instead, it suggests integrated solutions, such as using reflective materials and greenery, to mitigate the heat while retaining the benefits of renewable energy.
Professor Santamouris advocates for hybrid systems that integrate solar panels with water-based cooling solutions, which could help absorb excess heat and generate hot water.
"By cooling solar panels with water, we can improve efficiency and reduce overheating. We must seriously consider these integrated strategies to balance the urban heating challenges," he added.
In Bangladesh, the potential for rooftop solar energy is considerable, as the government’s Power System Master Plan (PSMP) suggests that the country could generate 635MW of electricity from rooftop installations, amounting to 17.3 per cent of its electricity supply.
A significant example of this is the rooftop solar power plant at the Korean Export Processing Zone (KEPZ) in Chattogram. Inaugurated in June 2021, the plant has a capacity of 16 megawatts (MW), with plans to expand to 40MW.
The study highlights that while rooftop solar panels are a vital tool in the transition away from fossil fuels, careful consideration and innovation are necessary to ensure they are effectively integrated into urban environments.
