Solar thermal drying plant for agricultural products. Part 1: Direct air heating system

Abstract

The need for sustainability, food security and to decouple food prices from the fluctuating prices of finite fossil fuels have driven the search for sustainable processing and the adequate storage of agricultural products. For this reason, a hybrid thermo-solar monitoring plant for the dehydration of foods was successfully designed and built in Zacatecas, Mexico. The thermal energy is provided by a solar air heating system with 48 collectors (111.1 m2) and a solar water heating system with 40 water collectors (92.4 m2). The overall energy efficiency of the field of air heaters was 39.49% with a power capacity of 46.14 kW. A batch test was carried out with direct solar air heating system, in which 288 kg of Nopal (Opuntia ficus) was dehydrated with an initial and final moisture content of 93.03% and 5.76% (wet basis), respectively, which was achieved in 17.62 h, with a maximum theoretical thermal efficiency of the dryer of 60.7% recorded for the first day of testing. Two financial scenarios were used to evaluate the economic efficiency of the solar air heaters; a conventional scenario, comprising a 24-month payback period; and, a scenario with added fiscal incentives, comprising a 17-month payback period.