You can see if that is the case by saving as a test. Sell the solar plant and see if the town shows a hydro plant.
As to the boost, that is easy to check as well. Look at teh number of shields you get in a given town. The base shields will not be increase by the hydro, if you do not have a factory.
Some towns are not worth building a facotry in as they do not NET enough shields. 50% boost in a 100% corrupt city will not net any extra shields. It will net extra maint cost though for the factory.