If you have the location (latitude) available and know how good the horizon/sky view is throughout the year, (is anything, like a tree or another building, or a mountain, etc, shading it for some of the year/day) and the weather, you should be able to know how cost effective solar is.
In some coastal areas, for example, the Bay Area, California in general, and many similar places, because of the coastal fog, or mountains, it likely also varies quite a bit from one microclimate to another.
How many days of sun vs. shade.
There must be a lot of software programs that do these kinds of calculations out there.