17 Sept : I have done a drawing to calculate precisely the position of the panels on our south wall. I dont want to drill holes through our external wall for 40mm pipes only to find that the holes are wrongly positioned. It's important to make sure that it will fit the attic trusses on the inside. In the attic, the pipes will be fully insulated and run the length of the house, to drop down to the heatpump on the North end. I have to ensure that the return pipe will miss the vertical part of the roof trusses. Also, each pipe needs an airlock release valve.
In this drawing, the flow is to the outer upper corners of the panels, and the return is from a Tee joining the panels together from the base. It is best for the pump to push the glycol downwards against the natural convection direction (upwards). This puts the panels into a 'parallel' arrangement with diagonal flow through the body of the panel.