Experimental analysis of evacuated tube solar air heater (ETSAH) with inbuilt sensible thermal energy storage

In the present work, an evacuated tube solar air heater (ETSAH) with inbuilt sensible heat storage material (SHSM) is experimentally evaluated. The system comprises two sets each having 50 evacuated tubes with an H-type arrangement and a total collector area of 16.92 m². For the purpose of hot air generation, ETSAH is simultaneously connected in series and in parallel with and without the use of reflectors. Three different mass flow rates of 122.90, 164.87, and 212.83 kg/h were fixed to get 12 diverse cases of ETSAH operation. The highest hot air temperature reported by the system is 121.7°C when it was connected in series with conventional reflectors at 212.83 kg/h of flow rate and 469 W/m² average solar intensity. The system reported an overall average energy efficiency of 49.76% and an exergy efficiency of 17.97% with the highest average hot air temperature difference of 56.12°C from 09:00 to 20:00 h. Without the incorporation of any additional SHSM, the average hot air temperature delivered by ETSAH (when under the neighbor building shadow) is 49.73°C logged from 17:00 to 20:00 h. The economic analysis is also carried out to ensure its practical application and feasibility. For the best system performance, the annual cost of hot air generation is 0.0194 Rs./kg (0.0002433 $/kg).