alt Hacker News> If something actually saves money then it doesn't require a subsidy because people would be doing it regardless.
…assuming people are good at math.
And given that most people probably don't have a bunch of cash just sitting there doing nothing, they will have to take out a loan and most folks probably don't like going into debt even though 'the math says' it's a good ROI.
The idea that 'ROI good, therefore people will do it' is the 'spherical cow' of economics. In reality there are all sorts of other motivations for human economic actions:
To be clear, this doesn't change the price floor for ROI calculations. A non "approved" contractor or DIY job non-subsidized is well cheaper than a piddly few percent interest rate arbitrage to a pre-approved list. This does nothing beyond let some rich contractors regressively allocate money from taxpayers to themselves by artificially appearing a bit less of a premium to the alternatives.
It looks more like to me some installers saw their industry was becoming commoditized and the government got together with them to figure out how to grift taxpayers into making the more connected ones command a premium while simultaneously being better positioned to eat the lunch of the small middle class "guy and a truck" who does cash jobs for cheap but has no resources to become "accredited" on a subsidization list.