There are two types of solar thermal panels – ‘flat panels’ and ‘evacuated tubes’. Both have their advantages and disadvantages.
Flat panels are heavier, less expensive for a given surface area and can provide more kWh of energy for each £ invested (although this can vary from product to product).
Evacuated tubes are lighter, produce more usable energy for a given area and perform better during the colder months.
Generally, where space is limited or the construction of the roof requires lighter panels evacuated tubes are preferred. If space is not limited, and the roof construction allows it, flat panels can be more cost effective. The maintenance of both is minimal and most products carry lengthy warranties.
There are specific situations, particularly in London where large parts fall into conservation areas, where certain products have distinct advantages.
For example on a flat roof, it may often not be permissible under planning regulations for the panel to be raised significantly above the ridge line. Normally you would want to mount panels at a 30°-45° angle to the Sun, so in this case evacuated tubes which can be laid flat and rotated towards the Sun are a good solution.
A Greener Place has a lot of experience with the planning regulations in London Boroughs and of the local roof types and construction and will be able to specify the optimal solution for you. Both types of panel work in conjunction with a solar hot water cylinder.