I have arranged installation of solar electric which has been a mixed experience of companies.
Getting quotes was the hard bit, to ensure that we got the right advice and the right price.
Once company chosen it all went smoothly.
Ensure the companies you ask to quote are signed up to the code of conduct ( REAL). Not listed then do not use them.
If you don't understand the technology, get some advice or a friend to help you ask the right questions, if a company is good they will be willing to explain things.
Get in touch with your electricity supplier early in order to register as they will only accept a reading once you have registered with them which may be after the system is installed and you will be losing out.