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)?
Best Answer
I realised I could just export my save and test this myself. The answer for anyone who needs it:
This will reset the building count to 0 (not replaced). The new building does not retain catnip effects. As upgrading destroys it is better to sell all your buildings to regain resources prior to upgrade.*
As you lose catnip effects don't forget to transfer more kittens to farming to pick up the slack.
*You may well go over your cap so do this carefully!