Techno-economic assessment of vegetable oils as heat transfer fluids for industrial solar thermal systems applications

This study evaluates sunflower, safflower, and rapeseed oils as alternative heat transfer fluids (HTFs) for medium-temperature parabolic trough collector (PTC) applications and compares their performance with Therminol VP-1 and Delcoterm E15. A validated thermal–hydraulic model (R² = 98.5 %), supported by experimental measurements on a 1.5 kWth PTC system in Morocco, was used to assess HTF behavior under three operational methodologies: fixed thermal power, fixed Reynolds number, and fixed mass flow rate. Results show that vegetable oils achieve slightly higher thermal efficiency (64–65 %) than synthetic fluids (62–63.5 %), attributed to their superior thermal conductivity and specific heat. Although their higher viscosity increases pumping demand, the associated penalty (12–15 W per 1.3 kWth) represents only 0.9–1.2 % of the useful thermal output, indicating minimal impact on overall system performance. At larger scales, vegetable oils offer substantial economic advantages: a 10 MWth solar field requires 400–450 k€ less initial HTF investment than synthetic oils. Application mapping shows that vegetable oils are best suited for industrial processes below 200 °C—common in food processing, textiles, and pharmaceuticals—while Delcoterm E15 remains optimal for 150–250 °C and Therminol VP-1 for >300 °C applications. These results demonstrate that vegetable oils provide a cost-effective, environmentally benign pathway for expanding solar industrial heat deployment, particularly in developing economies and small-to-medium enterprises.