For the ROI, I think that a lot depends on your local power costs, local construction/installation costs, and local solar availability. For us the locally high power costs dominated, as did our high installation cost, and relatively poor solar availability. For us, we decided to install solar when my ROI suggested a 7 year return on investment, including capital costs. Electricity rates that rose faster than projected drove the actual ROI to 4.5 years.
I can't say it often enough, but I think the economics of installing solar is hyper local. I've lived places where overcast skies predominate for much of the year, and that is going to make solar a lot less economical for most folks.
That doesn't mean that there might be non-economic reasons to install solar, e.g. grid independence, reducing a fossil fuel footprint, or improved resilience. YMMV (a lot).
All the best, Peter