A heat transfer fluid (HTF) is the fluid used to carry the solar thermal heat collected from a Concentrated Solar Power (CSP) field to the system’s main facility – for storage or active use. HTFs include water, oil, molten salt and silicone, and are selected depending on the temperature a system must achieve. Typically, specially formulated thermal oil or molten salt is utilized, especially for parabolic trough concentrators.

Thermal Oil

Thermal oil is the most common HTF for parabolic trough systems because it is easy to manage and capable of reaching a temperature of almost 400 °C. Various synthetic or organic thermal oils are readily available. The unique blend of thermal oil for a parabolic trough system is dependent upon the environmental conditions of the installation location.

Parabolic trough systems, like SkyTrough®, that utilize thermal oil have been used in hybrid and standalone plants for power generation or numerous industrial applications.

Molten Salt

Molten salt is often a mixture of nitrate salts (i.e. sodium nitrate NaNO3, potassium nitrate KNO3). The melting point of the salts are dependent on its blend, for example a blend of 60% NaNO3 and 40% KNO3 will become molten at 230 °C. Once molten, the salt can be introduced into a parabolic trough system, like SkyTrough®DSP. Depending on the blend, molten salt is capable of operating at 560 °C or higher, and can be used to bring water/steam up to the temperature required to run a steam turbine generator. This makes a system like SkyTroughDSP ideal either to be integrated as part of a hybrid system with plants that require such high temperatures or as a standalone alternative to conventional power plants.

Special components have been developed by SkyFuel for SkyTroughDSP to operate with molten salts and ensure that the system will function smoothly for years. In addition, as the experts of molten salt in parabolic troughs, SkyFuel’s engineers carefully design each field system to minimize the potential of a freeze event within the receivers.


Ultimately, the choice of system, and thus HTF, is dependent upon the desired outcome and site. SkyFuel can assist in the selection of system and HTF to optimize your solar field.