Sonnenkraft

I am contacting you because I have bought a solar colector and solar panels from Sotecnisol / SonnenKraft in 2011, under a 5 year warranty period, in Madeira, Portugal. Nevertheless this kind of colector is supposed to last around 20 years.My colector is showing internal corrosion since 2017 between the primary and secondary circuits and is no longer operating.I work in the area, and do solar colector reviewing frequently for scientific papers, so I know this was not supposed to happen and can only result from a severe construction failure.I also know that SonnenKraft during the portuguese campaign for solar thermal installed equipment bought from other manufacturers and those were of lower quality.I have been trying to contact Sonnenkraft but all I get from them are excuses such as that the problem comes from external corrosion (as if the it could reach the primary circuit).I have exchanged e-mails with the company for over one year and they know the kind of problem that originated this and that it is their responsibility, but they stopped replying me.I have bought one of the most expensive solar collectors to have quality not to have it working for 5 years.I am therefore requesting the replacement of the solar collector.Otherwise other costumers should be aware that this company is not reliable.