Performance evaluation of an indirect solar dryer with hybrid thermal retention elements for tomatoes

Tomatoes are widely used in Indian diets but its perishable nature restricts long term storage in fresh form. This study presents the development and performance comparison of an indirect solar dryer with pebble-based and hybrid pebble-paraffin wax Thermal Retention Elements (TRE) under similar operating conditions for drying tomato slices, considering energy efficiency, environmental impact, economic feasibility and nutritional preservation performance. Tomatoes were dehydrated from an initial moisture content of 93% to a final value of 12%. The hybrid TRE demonstrated improved thermal behaviour, reaching a maximum temperature of 48°C and sustaining 46°C even during periods of reduced solar intensity. This configuration shortened the drying duration to 26 h, whereas the pebble-based and open sun required 34 h and 46 h respectively. The average thermal efficiency of the hybrid TRE (43.5%) was higher than that of pebble based dryer (39.0%) and the annual useful energy of hybrid TRE (224.14 kWh/year) was also larger than that of pebble based dryer (200.95 kWh/year). This led to more CO 2 mitigation (13.99 t vs 12.54 t) and greater carbon credit benefits (202.89USD vs 181.98USD) throughout their 30-year life cycle. The energy payback period was 1.41 years for the pebble system and 1.26 years for the hybrid TRE system. Nutritional evaluation indicated improved preservation of vitamin C (14–42 mg/100 g), lycopene (4–9 mg/100 g), and β-carotene (2.9–8 mg/100 g) in hybrid TRE dried samples. The hybrid pebble-paraffin wax TRE provides a sustainable solar drying solution that is more thermally stable, energy efficient, and provides better product quality for small-scale agricultural food processing applications.