A good location for solar water heating (SWH) collectors is a south-facing roof which is free of shade has a tilt angle of between 20 and 50 degrees. However, even panels facing due east or west can face reasonably well.
The figure above shows how the performance of a solar water heating system depends on the tilt (pitch) angle of the roof as well as on the orientation. For example, the figure shows that a solar panel mounted on a south-west facing roof with a 40 degree tilt would produce 5% less output than a panel with perfect tilt and orientation. Even panels facing east or west can still produce 80% of the output of perfectly oriented panels.
Rooftop panels are the most common, but they can also be mounted at ground level. The SWH system heats water in a cylinder, therefore it is difficult to add solar water heating to a heating system that doesn’t have a hot water cylinder (e.g. a “combi” gas boiler which heats the water on demand when you turn on a hot water tap).
Roof mounted panels are usually a ‘permitted development’, so you won’t need planning permission. Exceptions include National Parks, Areas of Outstanding Natural Beauty, conservation areas and listed buildings.