Get three quotes is the most important factor here.
As many solar companies operate in different ways, it can be confusing to people like yourself. Generally speaking, if you have been canvassed on the doorstep, then someone has to pay the army of ‘canvassers’ from the ‘double-glazing’ school of salesmanship and that will be you the customer.
What many solar companies have been caught doing is mis-selling the returns and advantages (of course, there are many) to justify their very high-priced systems. Beware of this strategy when getting your three quotes. Smaller, more localised companies can offer more reasonable prices, because they haven’t got an army of sales teams and canvassers to employ.