Renewable energy-based drying of medicinal plants: enhancing efficiency, phytochemical retention, and quality.

Drying of medicinal plants and spices (MPS) is a critical post-harvest operation for extending shelf life and preserving bioactive compounds, sensory attributes, and nutritional value. However, most industrial drying practices remain heavily dependent on fossil fuels, leading to high energy consumption, increased carbon emissions, and degradation of heat-sensitive phytochemicals. Addressing these challenges requires sustainable drying solutions that maintain product quality while minimizing environmental impacts. In this context, renewable energy-based drying technologies, including solar, wind, biogas, geothermal, and biomass systems, have received increasing attention. This review systematically evaluates renewable energy-assisted drying systems in terms of energy efficiency, greenhouse gas emission reduction, and preservation of phytochemical and sensory quality. The analysis of existing studies shows that renewable and hybrid dryers generally outperform conventional methods by lowering energy demand and improving product quality. Despite these advantages, major research gaps persist due to limited process optimization, scalability constraints, inadequate long-term techno-economic assessment, high initial investment and maintenance costs, policy and regulatory barriers, and optimization studies constrained by high computational demands and the lack of standardized evaluation frameworks. Future research should focus on cost-effective and scalable system designs, integration of the Internet of Things and machine learning for real-time monitoring and control, comprehensive nutrient retention analysis, and long-term techno-economic assessments. By consolidating current evidence and identifying critical gaps, this review provides a framework to advance sustainable, high-quality MPS drying technologies for food, pharmaceutical, and cosmeceutical applications. © 2026 Society of Chemical Industry.