From Petroleum to Bio-Oil: A Mini Review of Renewable Heat Transfer Fluids for Solar Thermal Applications

The increasing global demand for clean energy has accelerated the search for sustainable alternatives to petroleum-based heat transfer fluids (HTFs) utilized in solar technologies. While conventional synthetic thermal oils exhibit strong thermal stability and effective heat transfer performance, they present several drawbacks, including high costs, reliance on fossil fuels, potential toxicity, and environmental risks associated with leakage or disposal. In this context, bio-oils derived from vegetable sources and biomass have emerged as promising renewable substitutes. These bio-oils are biodegradable, exhibit low toxicity, possess high flash points, and are abundantly available, particularly in developing countries rich in agricultural resources. Recent advancements in nanotechnology have further enhanced the thermal performance of bio-oils through the development of nanofluids that incorporate nanoparticles. This mini review examines the sources and production of bio-oil based heat transfer fluids, thermophysical properties enhancement, advantages, limitations, and contemporary applications of bio-oils in solar thermal systems. Additionally, it addresses current challenges and outlines areas for future research to facilitate the commercialization of bio-oil-based heat transfer fluids.