keep in mind another aspect when trying to get a contributory value of a component such as solar panels...the competition is NOT just other houses s that have solar panels...the competition also includes THE ABITLITY OF AN OWNER TO EASILY ADD SOLAR PANELS AT A FUTURE TIME )
Some components are very disruptive to add, months of construction, need to get building permits, zoning approval - for example adding a pool or workshop bldg ) But other components such as a adding a whole house generator, or solar panels....call the company, they take care of permits, they make it easy, they come out and typically install it in a day or two. These companies often offer financing, tax credits, rebates, and have the latest tech.
So a buyer may think, why should I pay 10k for these old solar panels, I would rather pay less for a house and in a year or two get brand new panels from that company with those nifty ads on TV