Review of vegetable oils behaviour at high temperature for solar plants: Stability, properties and current applications

With the possible depletion of oil resources and environmental considerations, vegetable oils are considered with great interest in high-temperature applications especially for solar plants. Many parameters affect vegetable oil stability, namely temperature, oxygen, moisture, duration of exposure to heat, etc. Conventional markers such as peroxide or free fatty acids do not always reliably indicate oil quality at high temperature. Evaluating the content of other degradation products such as polymers provides a better estimate. Reducing exposure to oxygen limits oil degradation. Vegetable oils have proven to be a favourable alternative to mineral oils in some applications, and several vegetable oils are commercially available. Their current use in solar cookers gives a good overview of their potential. Several reasons advocate for the use of vegetable oils in concentrating solar power plants: they are renewable resources, environmentally friendly, non-hazardous, highly available and less flammable products. Moreover, their thermophysical properties are similar, if not better, than those of thermal oils commonly used in solar plants. Despite these advantages, vegetable oils face some challenges, as for example their low oxidation stability. If the major challenge of using vegetable oils at high temperatures is their oxidation stability, the numerous environmental, economic and technological advantages make them innovative fluids for high temperature applications, particularly for solar applications.