Photovoltaics and Urban Microclimate: First City-Scale Study
Buildings are one of the key players in Europe’s solarization process (and beyond). Like ground-mounted solar systems, rooftop photovoltaic installations can also impact the microclimate, and it’s important to understand these effects. Especially if we aim to make rooftop solar panels a win-win tool in the energy transition.
For this reason, an international group of researchers from Australia, China, India, and the United States decided to evaluate the potential effects of widespread rooftop photovoltaic adoption on urban temperatures.
Solar Panels on Roofs Can Influence Urban Temperatures
Using the Weather Research and Forecasting (WRF) model, the study comprehensively analyzed the impact of rooftop solar panels on a citywide scale, using Kolkata, India, as a case study. The team studied the impact on the urban microclimate with varying levels of photovoltaic coverage. They also conducted sensitivity studies specific to Sydney, Austin, Athens, and Brussels, comparing these results with those from Kolkata.
“We found a linear relationship between temperature increase and the percentage of roofs covered by PV,” said Professor Mattheos Santamouris from the University of New South Wales, who led the research. “In the maximum scenario of 100% coverage during peak summer periods, our data shows that rooftop solar panels cause a significant increase in daytime temperature.”
However, at night, infrared heat transfer results in the surface temperature of photovoltaics being lower than the urban temperature, thereby lowering the surrounding air temperature. The authors consider this a crucial benefit, as global warming’s impact is most acutely felt (and will increasingly be so) at night.
Overall, the study found that in a scenario of complete PV coverage in a city, urban temperatures could increase by up to 1.5°C during peak summer periods and decrease by up to 0.6°C at night.
How to Prevent Photovoltaic Modules from Heating the Air?
Avoiding daytime heating is not only possible but would allow photovoltaics to operate more efficiently, leading to increased energy production.
How? By using advanced cooling strategies in rooftop solar systems. For instance, hybrid photovoltaic systems that integrate solar panels with a thermal water-based collection system can absorb excess heat and recycle it domestically. Another option: “Combining photovoltaic panels with green or white roofs could increase their capacity by up to 6-7% and significantly reduce surface temperatures,” explains the Professor.
Benefits of Rooftop Solar Photovoltaics
Why is it important to continue investing in this direction? Because the same study also found that rooftop photovoltaics can have additional positive effects on local conditions. Specifically, they can reduce pollutant concentrations by increasing the planetary boundary layer. What is this? It’s the portion of the troposphere directly in contact with the ground and influenced by surface conditions. Photovoltaic modules could increase wind speed, thereby diluting contaminants.
“Rooftop solar panels also improve the penetration of coastal sea breezes further inland in coastal cities, while reducing ground-level pollutant concentrations,” says Prof. Santamouris. “This somewhat compensates for the increased daytime temperature and is particularly important for cities like Kolkata, where air pollution is a serious issue.” The study was published in Nature Cities.