Sensors location for PV Water heater

Sensors must not impair the appearance or operation of the house. 
There is no problem for authorization to install a solar water heater, except in certain designated sites. Anyway, it is better to ask at your local town hall, if a statement of work is necessary.
In the case of new construction, it is recommended that the integration of sensors in the roof, or as an architectural element, such as an awning. 

The sensors are required on the drawings of the building permit.
There are several types of solar water heaters, but,Unfortunately, some are not suited to the UK climate because of the danger of frost. 

Thus we need a system designed to use an antifreeze fluid to transport heat sensors to storage tank. The hot water then is heated via a heat exchanger inside the ball.