Solar collector systems to provide hot air in rural applications

A simple solar system is designed and studied, its thermal performance and economics are evaluated. A mathematical model and a code are developed based on monthly average meteorological data. The collector field is built using indigenous and locally available materials. Two kinds of solar collector field are considered: (i) collector field for which the ground is used as absorber and with glazing; (ii) collector field for which roofing sheet is used as absorber without glazing (bare absorber plate collector). In a case study, the system is used to provide thermal energy for drying tobacco in an existing propane burning heating plant at Bokito, Cameroon. The results showed that in the first case, the thermal efficiency is about 38%, the useful annual solar energy collected is 2.592GJ/m2/year and the cost of thermal energy is 2.03 $/GJ, and in the second case, the corresponding values are for collector with galvanized iron roofing sheet absorber, 22%, 1.443GJ/m2/year, 1.46 $/GJ, and for collector with aluminum roofing sheet absorber, 24.5%, 1.650GJ/m2/year, 1.28 $/GJ. The estimated solar energy cost compares favorably with the thermal energy cost of 36.5 $/GJ from the existing propane fired system.