I am working on an appraisal of a ranchette type property, the owner recently spent $40,000 for solar panels and $10,000 for a structure(carport) to set them on, unfortunately there are no sales with solar panels. The owners stated that he has a 10 year payback, (more like 12-15). What type of adjustment would be realistic in the Sales Comparison Approach? Anyone with experience in this area? Thanks in advance. I should also add the subject is on the electric grid and has a bi-directional meter that will run backwards when the residence power use is down. The owner calims to only have a $4 per month bill right now.