The assembly should be carried out by a qualified person, due to the fact that wrong assembling can lead to the Solar Water Heater malfunction and to hazard of the electric shock.

The transmitter-sensor frequency ISM band 868 MHz device should be mounted to the construction of Solar Water Heater in shadowed from the sun place below the hot water tank and behind solar collector. 
The holes in the metal sheet (ground plain of antenna) on both sides of Transmitter-Sensor Device box could be used for fixing to the construction of solar water heater will help of proper cable ties.

Temperature sensor usually is placed behind thermostat. For better contact between thermal side of thermostat and the temperature sensor cable tie should be used. 
PV panel 6VDC is equipped with magnets which allow for quick and very easy installation on the side of solar collector. Very important is to check if all over the day the sun shadow does not cover the PV panel.

Equipment specified above conforms to as follows standards:
ETSI EN 301 489-3, ETSI EN 300 220-2

Manual