Fun article on how rooftop solar panels are the new granite countertops.
Look. Insulation is fundamental. It's still a LOT cheaper than solar. Three inches of insulation underneath the slab is a very cost-effective way to save on energy bills (if you live in a place with cold winters). Having an airtight building envelope is also an extremely cost effective way to save on energy.
But as the article points out, a 3KW rooftop system is less than $15K installed, and the article forgot to mention you get a 30% Federal Tax Credit as well.
So roll the cost into your mortgage, get the tax credit up front, and enjoy much lower utility bills.
You are "cash flow positive month one".
Mrs. Angus and I are doing exactly this in Santa Fe. Because our house will super-insulated, air-tight, and fairly small, we are only doing a 2KW system (we will have a separate thermal solar hot water system as well). We get a 10% state tax credit to go with the 30% Federal. We will be getting like $7 / square foot of tradeable state tax credits from the Build Green New Mexico program. We also dispense with the nastiest part of residential solar, the batteries and storage, by having our system be grid-tied. That is, we sell our power to the utility company, and they sell power back to us at a lower rate.