This info hasn't propagated to the Wiki yet and I can't find any info online about it.
Next to the Aqueduct and Pasture I now have a caret symbol (^). This allows them to be upgraded to a Hydro Plant or Solar Farm respectively (source: Buildings Wiki page). Both are listed as producing energy.
On clicking to upgrade you get the following warning: "Do you want to upgrade building? You will lose all existing buildings."
I've got quite far on my first play through and don't want to screw it up/murder all my kittens. Will this reset my buildings to 0 in both categories (completely destroying them instead if replacing them)? Do the upgraded buildings retain their catnip benefits? Is it better to sell the existing buildings before upgrading (getting back my resources)?