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Modeling shows green roofs can cool cities and save energy
(techxplore.com)
This is a most excellent place for technology news and articles.
8% reduction in peak AC usage would be huge. I don't have a good feel for numbers like that but I'd imagine it would take a lot of maintenance and roof replacements not not make a saving given that kind of energy reduction.
It would be nice if they could estimate some uncertainties and show where the break even is between energy reduction and upkeep energy expenditure.