thermal collectors solar energy sources 39 solar cells 17 photovoltaic cells 6 water heaters 4 roofs 4 heating 4 more ... untraditional sources heating 4 biomass 3 buildings (architecture) 3 unconventional energy sources 3 dwelling houses 3 solar power stations 3 solar radiation 3 thermal pumps 3 cooling mechanisms 2 history 2 metal constructions 2 assembly 2 low energy buildings 2 thermal insulation 2 caloric output 2 absorption processes 1 architectural designs 1 architectural elements 1 bionics 1 means of transport 1 effectiveness 1 electronic circuits 1 water energy sources 1 less ...