Be careful with installing solar panels. Use a reputable installer.
If you own them outright lenders are happy but if you lease the airspace make sure all is lender compliant. .
Make sure that Building Regulations Consent is obtained and that your roof is structurally sufficient to hold them
Feed in Tariffs can also be a concern on resale. Have they been sold on to someone?
See UK Finance Mortgage Lenders Handbook (CML Handbook) and ensure the scheme is compliant.
Read more here about investing in solat panels ...