We have the hot water tank installed! It was a tight fit in the corner and in hindsight the design of the walls in that corner, should have allowed for a deeper cupboard by moving the windows along a bit.
All the pipes going up and down are in around the tank including the copper pipes for the solar panels (copper pipes is used as the pressure and temperature in a solar heating system can be higher and plastic pipes are not rated).
The tank is surrounded by another 50mm thick of PU foam to maximise the energy efficiency while the water is heated up by the Sun.
GR Hot water tank
GR Hot water tank