Hi Adam, Toolstation do a reasonably priced product Barrettine Mould & Mildew Cleaner 4L

Hi Adam, from the images it appears that the clamps holding the panels to rails may be incorrect and/or overtightened not spreading the weight which may be causing areas of stress on the panels. You may also find that the moisture ingress may cause a short from the frame to the rails and roof. It also appears Roof Lichen has started to anchor itself on your PV panels and roof. There are many cleaners on the market, but to keep it back you will have to clean the roof and the panels.