"Is X monetizeable", "can X generate enough traffic","does X have potential" imho, the answer to these questions will probably take equal effort to the technic

"Is X monetizeable", "can X generate enough traffic","does X have potential" imho, the answer to these questions will probably take equal effort to the technical/development aspect. There are plenty of price comparison engines around... so if a domain expert in solar thought of this idea and did all the market research (to have the answer to your question), I suspect they would be developing a competitor.