OP if you are just going to do the solar panels only, make sure you disclaim in a contract what you are and are not doing. And Error and Omission insurance is a good idea for any type of inspections. Here in NJ this starts to get cloudy. In NJ you do NOT have to be a roof contractor or home inspector to inspect solar panels, but when you start to make judgement on the roof it sits on, you are in a gray area. Make sure you speak with a lawyer, others doing this type of business in your area and a general liability and error and omissions insurance agent (insurance reps can talk to lawyers specializing in these fields they may have on retainer). Also don't forget about a certification (Helps to establish your credibility) in thermography. I am currently in Home Inspection school and my teacher always says "In this business it's not if you get sued, but when".
Good luck in your business!