The work focuses on experimental analysis of two solar process heat plants with parabolic trough collectors quantifying daily and monthly inner energy ΔU required to heat-up heat transfer fluid and piping system and comparing it to useful solar energy gains Q_use. Both plants analyzed provide solar heat for dairies and are located in northwest (Saignelégier) and southeast (Bever) of Switzerland. They operate at different collector temperatures (120 °C/190 °C) and differ in size (627 m²/115 m²), integration concept (hot water/steam) and type of heat transfer medium (water-glycol/thermal-oil).