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- cross-posted to:
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Rooftop photovoltaic solar panels warm up and cool down cities in Nature Cities
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after building a more detailed simulation than prior models that solar panels increase urban temperature variations, causing the five simulated cities to be hotter during the day and colder during the night.
Important bit here seems to be its a simulated city, fwiw. Though I can see the logic
I’m not sure of the validity of model, though I appreciate the effect of cooling at night.
Without solar, ground, usually fairly dark, absorbs solar heat at 100%. Solar panels cover 75%-80% of this heat to electricity, and while they get hotter than lighter shaded ground, the heat capacity of dirt is much higher, and the heat is lost quicker from air/wind contact. Similarly a building that has a solar cover with a slight airgap, will be cooler during the day than without solar, and using less AC, produce less warming surrounding the building.
For cold areas, snow cover actually retains warmth in soil. With bifacial panels, increases winter production significantly. No airgap over buildings, is path to keeping more heat for building, but using an airgap to help preheat air or water pipes for heat pump is just another path of using environmental heat to focus on useful heat. Heat pumps for heating (vs cooling) in general reduce outside temperatures.
Realize I’m replying to myself, but does this heating take the actual climate heating that is ongoing due to continued fossil fuel use?
What do you mean by “take” here?
I suppose “accounting for” would’ve been a better description
I’m sure nobody is going to use THIS is bad faith. What could go wrong?
At the same time, these larger temperature swings result in higher wind speeds and potentially greater pollution.
The greater pollution they’re talking about is:
Also, greater pollution is possible due to the higher temperature differential between the ground, rooftop, and sky above that mixes smog, dust, and other pollutants into the air.
Pollution that already exists, just possibly spread around a little more.
I also didn’t see anything about their assumptions about solar panel-less roofs. Going to be pretty big differences if they’re assuming the Un-paneled roofs are all painted white, vs black, for instance.
We could get rid of individual car traffic in cities to compensate for both. :)
The theoretical explanation:
When RPVSPs are installed on roofs, they absorb a significant amount of solar energy, converting some of it into electricity but also generating heat in the process. This heat is released into the surrounding air, leading to an increase in air temperature around the panels. Moreover, the elevated installation of RPVSP creates two hot surfaces: the top surface of the panels and the underside surface. As air flows over these RPVSPs, it picks up heat more efficiently than it would from typical building or ground surfaces. Observational studies in the literature have shown that areas with RPVSP arrays can experience higher daytime air temperatures compared with reference sites without RPVSP.
In essence, the heat that would be absorbed by the building (requiring more energy for cooling the interior) is instead absorbed by the panels and conducted to the surrounding air which creates a convective heat exchange cycle on a city wide scale. It would be interesting if this were compared to awnings (and pegodas) that have been in use for centuries for passive cooling of space in and around buildings.
Further, It seems like this would call for the use of phase changing material to absorb the heat from the back of the solar panels which would reduce this intensification of the urban heat island effect as the heat energy would be use in the phase change process during the day and slowly released in the reverse phase change at night without conducting more heat into the building.
None of this seems to have any real consequence on the global warming effects of greenhouse gasses (primarily natural gas [methane] and Carbon Dioxide). But it is a more accute concern that is more likely to be addressed through local ordinances, laws, and regulations.
Also, the paper casually mentions how rooftop solar reduces the cooling load of the building. What I didn’t see acknowledged was that that extra cooling load (presumably traditional A/C) on a building without rooftop solar moves the heat out of the building into… (drum roll), the surrounding environment. So… the heat still got to the surrounding environment, it just took a longer path to get there.
this would call for the use of phase changing material to absorb the heat from the back of the solar panels
There are quite a few “better” technologies for cooling solar panels, which happens to also improve their efficiency/production.
Thermoelectric devices would boost production a little, and keep production a bit past end of day. This might not yet be cost effective, but massive production scale could change that. Circulating water behind the panels, transfers the most heat, and hot water is useful to everyone. A simpler, leak proof, technology is to suck in air behind/under the panels that creates a flow that will cool them, and use that hotter air to feed a heat pump.
Those all seems like very workable options.
Looks like no one can win
