alt Hacker NewsI have been wondering: more solar means we are making Earth less reflective. Solar energy that might have been reflected back to space is now absorbed by the PV to make electricity. But that delta has to go somewhere? Where does it go in terms of Earth’s temperature. Same with more nuclear… we’d be pumping more energy into the system.
Don’t take this as an argument against these technologies. It’s a huge win to not be increasing the CO2 concentration in the atmosphere by burning fossil fuels.
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We're actually heating the earth in two ways... one is by increasing the greenhouse gases in the atmosphere. The other is simply by using energy; any use of energy means moving something to higher entropy and thus producing heat, even if that energy comes from 100% clean or renewable sources. However, nobody talks about this second way of heating the earth because it's about two orders of magnitude behind the first, i.e. for now pretty insignificant.
As for making the earth less reflective with PV panels... yes, you are right and most of that absorbed solar energy directly contributes to heating the earth because PV panels aren't anywhere near 100% efficient in converting it to electricity, but even the part that is converted to electricity will become heat again in the end, like when it powers AI data centers. (If PV was 100% efficient, then the lack of reflection wouldn't directly do any heating, the heating would all happen when the electricity is used.)
For now that isn't a big concern because the greenhouse gases our civilization is releasing into the atmosphere do so much more heating than all our use of energy, but if we do become 100% renewable and survive that particular danger, then by Jevons' paradox we'll soon be using 10x to 100x more "clean" energy and be heating the earth all the same again.
A solar array makes the earth less reflective by a fixed amount, for as long as the array exists.
Every unit of fossil fuel we burn makes the earth permanently less reflective (or at least something on the order of 100 years). You could compare a 1GW solar array (for its lifetime) to a 1GW coal plant running for x days, though I don't have the value of x.
Current levels of solar panel coverage on Earth are approximately 0%. If we ran the entire Earth on Solar power we’d need ~ half a million square kilometres, around 0.1 percent of the Earth’s surface.
Yes, this does happen. Solar farms have an albedo modification effect. The good news is that compared to fossil powered generation, the albedo modification is "paid back" in less than a year due to lower GHG emissions:
"Small reduction in land surface albedo due to solar panel expansion worldwide"
https://www.nature.com/articles/s43247-024-01619-w
If you download the supplementary information PDF, figure 19 shows a plot of GHG payback times by site. The most common time is about 1 month. The greatest time they found was about 9 months. These times go down as solar panel efficiencies continue to creep upward, because solar panels in 2026 don't have lower albedo than in 2024, but they do have better light-to-electricity conversion efficiency.