The questioning of the heating plumbers — the heating plumbers are in fact the most important customers for the solar technology companies — supplies considerable input to the specification of an optimum collector. Therefore, 30 plumbers in the region of Ingolstadt were contacted and personally interviewed using a list of 24 questions out of different areas of their business, mainly in order to find out deficits and optimisation potentials of solar-thermal collectors.

It became clear that solar-thermal systems still suffer from the high amount of labour required for the roof installation of the collectors. Apparently, % of the contacted plumbers need to visit the installation site twice with up to three workers.

More than 40 % of the plumbers considered the glazing and the fixation to the roof as the major sources for complaint and repair. In this respect, У of the questioned plumbers named the sealing of the collector itself. Remarkably, only % of the plumbers had to deal with leaking pipes.

Concerning the roof installation, the questioned plumbers named the aspects shown in figure 2. Still, collectors with sharp edges annoy the workers. The plumbers clearly ask for a shift of installation work from the roof down to the ground (first steps of installation). Additionally, they ask for improved devices for the transport of the collectors onto the roof. Number one of the plumbers’ troubles, however, was the high weight and the difficulties to handle those heavy and big collectors.

Hence, the heating plumbers clearly ask for improvements concerning the weight and the handling of the collectors.