“…Online available publication series, meta search engines (Google scholar) as well as bibliographies (among others the index of the German National Library) were browsed to select references regarding relevant catchwords like "renewable energy", "renewable energy services", "services", "technical operation" and "maintenance". Publicly available information of renewable energy providers was used in addition to literature research identifying relevant sources (Albers, et al, 2002;Allnoch, et al, 2010;BMU, 2011;Bührke & Wengenmayr, 2007;Faulstich, et al, 2011;Pelte, 2010;Watter, 2009;Wesselak, 2009).…”