Evidence-driven global strategies and knowledge exchange are essential to address urban overheating and to reach net zero emissions by 2050.
The widespread adoption of rooftop photovoltaic solar panels without cooling can inadvertently raise temperatures in our cities, according to a UNSW-partnered study.
The study used advanced simulation technologies at a city scale to understand the climatic impact of installing photovoltaic solar panels in Kolkata, India over the course of a year.
It found city-wide installation could raise daytime temperatures by up to 1.5°C, but potentially lower nighttime temperatures by up to 0.6°C.
Material advancements have made photovoltaic solar panels more efficient and accessible (lower in cost), making them a promising renewable energy solution, says Scientia Professor Matthaios Santamouris from UNSW’s School of Built Environment.
“However, their lower albedo [ability to reflect light and radiation] and their thermal characteristics can lead to an increase in heat absorbed and transferred between solar panels and underlying roof surfaces,” the Anita Lawrence Professor of High-Performance Architecture says.
Photovoltaic solar panels decrease in efficiency the hotter they become. “This heat is emitted into the urban atmosphere rather than converted into usable electricity.”
This surplus heat can also impact the exchange of energy and meteorological fields (such as wind, pressure, humidity) at the Earth’s surface and near surface respectively as well as altering sea breeze circulation.
This impacts energy consumption patterns, for example, increasing the need for cooling.
“Understanding and mitigating these effects is crucial for balancing the benefits of renewable energy with its potential impacts on urban climates,” Prof. Santamouris says.
Prof. Santamouris is ranked as the No. 1 Highly Ranked Scholar in the world in the fields of Architecture and Urban Heat Island by Scholar GPS, 2024. He and his team are involved with more than 200 large-scale heat-mitigation projects around the world in Europe, the Americas, Asia and Australia.
The study was a partnership between the University of Calcutta; Indian Institute of Technology Kharagpur; Massachusetts Institute of Technology; Jadavpur University; Royal Meteorological Institute of Belgium; Chinese Academy of Sciences; University of Texas; and UNSW Sydney.
It provides a comparative analysis with cities, such as Sydney, Austin, Athens and Brussels, demonstrating valuable insights for policymakers on managing large-scale solar panel installations.
Australia should follow the lead of Europe and the United States in their widespread use of hybrid photovoltaic-thermal solar panels, Prof. Santamouris says. Hybrid systems repurpose surplus heat, for example to heat water, as well as generating electricity.
While hybrid panels are more expensive upfront, when cooling costs and additional benefits are taken into consideration, this is marginal, he says.
“Our research demonstrates the need to implement sustainable technologies targeted for local climate conditions. There is absolutely no need to put more heat sources in the city.”
Addressing climate and energy security is now urgent as human activities continue to warm the planet, Prof. Santamouris says.
“Overheating is intensifying very fast. Prior to 2023, the rate of global overheating was 0.2 degrees per decade. In the second half of 2023, mean land and sea surface temperatures overshot previous records by up to 0.2°C, a significant margin.
The McKinsey Global Institute reported that the transformation of the global built environment needed to achieve net-zero emissions by 2050, set out in the Paris Agreement, should be “universal, significant and front-loaded” with the next decade “crucial”.
This will require an estimated US$1.6 trillion in annual average spending on building and construction. With this level of investment demands, it is critical we follow evidence-led solutions targeted for local environments, he says.
“For example, green roofs offer a nature-based heat mitigation strategy that bring other ecological benefits, such as storm water management, a reduction in pollution, and urban aesthetics.
“Our research shows extensive green roofs [which have a thinner substrate] are a viable technology in Seoul, Korea, but they are expensive in the Australian climate. Here, we can get better results with less expensive strategies, such as super cool roofs or similar high albedo materials.”
Installing super cool roofs, pavements and coatings for buildings that reflect rather than absorb solar energy would allow us to reduce peak temperatures in our cities by up to four degrees, he says.
“These materials counteract the effects of climate change as well as saving people’s lives.”
Overheating brings economic and energy equity issues, as evidenced during India’s 2024/2025 heatwaves, he says. In April 2025, extreme heat arrived early with temperatures above 40°C, around 5°C above seasonal norms. This affects morbidity and mortality rates, livelihoods and water resources across the country.
“People went to the supermarket to buy an air conditioner – it was really affordable – but to run air conditioning you need electricity supply,” he says. Peak electricity demand surged by close to 15.4% as a result. “This requires 15% more power stations per year. There’s no country that can manage that [level of investment].”
Plus, investing in new infrastructure drives up the cost of electricity, pricing out lower socio-economic groups, he says.
While the Indian government banned the installation of air conditioning without previous approval, this is difficult to implement on the ground. “The result: during the heatwaves, people had electricity for just four or five hours a day.”
The issue is widespread; closer to home in remote Australia, one in three households have issues with electricity supply during heatwaves, he says.
“It is estimated they will cut the electricity supply to 150,000 households by the end of the year. The majority of these households are Black and Hispanic populations.”
“The social impact of climatic change and urban-level heating on low-income populations is tremendous. The population is suffering.”
The UNSW High Performance Architecture team has delivered training on mitigating urban overheating and promoting thermal comfort to help build global climate resilience.
The World Bank-supported initiative addresses the growing challenge of urban overheating in rapidly expanding African cities like Dar es Salaam, Tanzania.
“Dar es Salaam is one of the fastest growing cities in the world. It is well known that as cities grow, the loss of green space and the increase in roads, buildings and other infrastructure will cause heat-island effects,” Prof. Santamouris says.
In May 2025, the team delivered workshops in Arusha, focusing on climate-adaptive urban design and city-cooling strategies. The program brought together engineers, architects, policymakers and stakeholders from across Tanzania to explore practical, equitable solutions for improving thermal comfort and health in urban environments.
“Our training is a way to share solutions that work for everyone in a city, regardless of income or access to technology,” he says. “I want to share this knowledge as widely as possible, as implementing advanced heat technologies can deliver very important health, sustainability and economic benefits."
School of Built Environment
Scientia Professor Mat Santamouris
