This standard defines the test methods for determining the physicochemical properties of organic synthetic fluids used as heat transfer fluid (HTF) in solar thermal electric plants with parabolic trough collector technology, both new and having been in service, and the measurement techniques suitable for the determination of its characteristic parameters. This standard is applicable to solar thermal electric plants of any size that use concentration systems with parabolic trough collector technology, with the Sun being the main source of energy. Such plants may optionally have non-solar energy sources, such as natural gas or other renewable energies, and a thermal storage system.