Modelling shows that widespread rooftop solar panel installation in cities could raise daytime temperatures by up to 1.5 °C and potentially lower nighttime temperatures by up to 0.6 °C
https://www.unsw.edu.au/newsroom/news/2024/10/rooftop-solar-panels-impact-temperatures-during-the-day-and-night-in-cities-modelling
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G’day r/science, sharing the above study led by Dr Ansar Khan from the University of Calcutta that’s been co-authored by our Scientia Professor, Mattheos Santamouris. The study has been published in Nature Cities if you’d like to check it out: [https://www.nature.com/articles/s44284-024-00137-2](https://www.nature.com/articles/s44284-024-00137-2)
The study found that widespread rooftop solar panel installations have a number of effects on cities including day and night heating and cooling effects, urban surface energy budgets, near-surface meteorological fields and sea breeze circulations.
The study used mesoscale simulations due to the absence of available observational data for rooftop solar panels to model their impact on local climate conditions at the city-scale.
Please note that the study does not suggest that solar panels aren’t an important renewable energy solution in the transition away from fossil fuels. Instead, the researchers say it highlights the opportunity to develop integrated solutions for rooftop solar panels to balance their benefits with their potential drawbacks in urban environments.
*Prof. Santamouris says the heat effect of PVs at 100 per cent rooftop coverage would curb much of the renewable energy benefit. Estimations show that in Sydney, almost 40 per cent of the electricity PVs produce is used to compensate for the overheating impact, opens in a new window in additional cooling load – mainly air conditioning.*
Well that’s not great.
Covered parking lots. Make it so if some idiot strikes a post it doesn’t fall.
Cities not being easily sustainable in any way isn’t a surprise. We need to spread out.
Sounds like they were only looking at the effects in summer, but certainly the claim that “40% of solar rooftop energy was consumed” to compensate for the higher daytime temperatures in areas with high solar roof concentration is a bit concerning. I’d think the opposite would be true in winter though, giving an outsized benefit by reducing the need for heating.
Certainly seems like a topic that needs some more research.
So the real world data cited indicates a net cooling effect, but the models suggest otherwise? Could it be that the models are inaccurate?
The mechanism wasn’t immediately obvious to me, so I RTFA.
The short of it is that of the energy that hits the panel, some is converted to electrical energy, while some is absorbed, manifesting as heat. The panels can reach 70 degrees celsius. In the absence of panels, the roof typically has a higher degree of reflection, and so doesn’t reach as high a temperature. I was surprised by this as I would have thought that the fact that wind can flow both above and below a typical panel installation would have provided sufficient cooling to not make much difference.
The bit I still don’t understand (that is perhaps explained in the underlying paper?) is how this would impact anything other than the top level or two of an apartment building. Surely by the third floor down, the heat effect would be negligible, and so all those residents would not be expected to increase their use of AC?
There is next to zero real information in that article, and I didn’t go to the nature article but I’m wondering on what kind of roof without panels they are comparing it to. My roof is slate gray steel panels, one neighbor has bright red steel panels and the other has black asphalt shingles. I’ve seen flat roofs with white dolomite gravel on it. They all have different temperatures signatures.
I have to question the validity of this. There is no way it relates directly to the building the roof top solar is on. The air gap between the solar panels and rooftop reduces the solar heat gain on the roof reducing energy used for cooling.
There may be a local air temperature increase if the roof that the solar is covering was lighter than the solar panels, but if the roof was the same or darker, then the air temperature increase would be negligible.
This can also be seen in fields with solar arrays, they reduce the heat load on the ground and allow plants to grow when they otherwise might not due to water evaporating out of the soil.
Are we sure this isn’t propaganda?
If it’s rooftop couldn’t you start integrating with plumbing to do some water cooling if it’s so impactful?
Modelling is great, but the outcome is really a function of the assumptions and the accuracy of the model. So I assume the black color of most solar panels will absorb a broader sunlight spectrum and thus increase the heat. I wonder what their assumptions were for standard roofing colors. Black on black or black on brown would seem to have little or no impact. Black on white or reflective silver would have a larger impact. Additionally, the roof area of a sky scraper (multistory building) compared to the entire outer area would seem to have a limited contribution to the overall heat absorption, plus you have street heating, … I am skeptical.
I’m sure I saw a proper gander leave the restaurant as I went in!
Shout out to anyone who recognized the source …