Comment on Why can't countries with vast deserts make solar farms to power the world?
porksnort@slrpnk.net 16 hours agoHow do solar panels create a heat island? They shade the ground beneath them. There have been installations where panels installed on buildings saved money on cooling costs before the panels were even connected, due to the shading from the panels.
Am I missing something?
The only thing that makes sense is that they absorb heat that would otherwise be reflected away, right?
in the building example, they’re essentially insulated against a specific mass by air gap behind them, and in the heat island example, the area of concern is larger and the panels are included.
How is dirt different from a building in terms of thermal mass? It’s the same setup. Panels can shade buildings just as well as dirt. It’s actually a super complex situation that depends on a huge number of variables.
I’m pushing back because this common trope (solar panels cause heat islands) was part of a whirlwind of anti-solar FUD about a decade ago.
The moronosphere turned some wonky studies that showed some local heating effect (in some situations, not all) into a panic about it causing mega-storms and causing dogs and cats to want to live together.
Since then, actual experts have been working hard to understand the costs and benefits of large installations.
An example:
Have you been in a desert at night? It gets cold, fast. Have you ever dug a few inches down into sand and touched it? It’s much colder than the blazing surface in the summer. Deserts to not typically have dirt, they have sand. Black panels shading a typically black roof will of course decouple the heating from the building. Black panels shading a very pale, very reflective, very insulative ground material is going to absorb and retain more heat
When attached to a building, the panels transmit a small amount of the absorbed heat to the building - less than would otherwise be absorbed by the building if the panels were not shading it. The building’s thermal energy is what is being measured, not that of the space including the solar panels.
When in an open space, the panels absorb more heat than would otherwise be reflected out of that space if they were not there, but they contribute to the total thermal energy of that space.
Not sure how it works but the effect has been studied
ChaoticNeutralCzech@feddit.org 15 hours ago
They’re black, duh. Yes, some 20% of incoming energy becomes electricity but the rest gets turned into heat. A reflective (white) material heats up way less.
porksnort@slrpnk.net 15 hours ago
So you ignored the fact that it’s not the earth that is getting heated, it’s the panels. So when the sun goes down the thin panels and the air around them cool down quickly, much more quickly than a large mass of hot rocks and dirt.
‘Thermal mass’ is a huge factor here. You ignored the basic finding that buildings with panels on the roof are cheaper to cool just because of the shading effect of the panels.
ChaoticNeutralCzech@feddit.org 13 hours ago
Panels are effectively part of the earth. It’s one closed system.
You do have a point: a black body radiates more heat than a high-albedo one so at night, the panels can cool down below ambient temperature. Overall, low albedo (reflectivity) and small thermal mass causes higher temperature differences between day and night – and it’s daytime when people want cooler temperatures.
But yes, any shade will help people living below solar panels feel cooler on sunny days, which is why I advocate for building a solar roof over just about every parking lot.