I hesitate to enter this fray, but here is a Solar Calculator (below). Seems the average payback is 12-15 years. Punch in your zip and see what others got or even your own address. Of course there are variables, as always. I only see energy prices going up.
As you said @snagged in outlet 3, updating HVAC is a huge energy saver as well as lighting--LED vs CFL vs halogen vs incandescent (who GW Bush eliminated btw). LCD TVs pull half the watts as old tube TVs--so newer tech pulls less power. Newer energy star appliances help. Old fashioned farmhouse architecture with eves providing shaded over windows helps. As @ColdWaterFshr said, LEED architecture is more than a hobby and can make a building profitable. This isn't political spin, just facts.
https://www.energysage.com/market/start/