According to the report published on global water stress, the world will face a huge water crisis by 2040, due to continuous decay of freshwater resources and an increasing population of human beings. To fulfill this increasing demand for freshwater, we need to find a new source. As the sea contains most of the water available on earth, desalination of sea water can be a solution. Furthermore, the use of solar energy for desalination process can make it a sustainable solution. This is why it is very important to work on solar thermal desalination system. In recent years, a lot of research has been reported on solar still integrated with evacuated tube collector (ETC) to improve its efficiency and productivity. But the problem of salt deposition in evacuated tubes was very common in these systems. So in the present work, a new solar thermal desalination system based on ETC is developed. In the present system, ETC is integrated with a storage tank, which further has a heat exchanger. Therminol 55 is used as a working fluid, which transfers heat from ETC to saline water. System performance is evaluated in terms of productivity, energy efficiency, exergy efficiency and economic feasibility. The productivity of the system is 4.2 L/m 2 /day. The average energy efficiency delivered by the system is 43.92% and average exergy efficiency to be 9.53%. The maximum mass flow rate of thermic fluid is

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).

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For the purpose of low‐medium air heating applications like timber seasoning, HVAC, agricultural & food drying, space heating and desalination, there is requirement of hot air. Solar air heaters are the promising systems to satisfy these requirements in a very inexpensive manner. Due to higher efficiency at higher operating temperature and lower cost, evacuated tube collectors (ETCs) are preferred for solar air heating. In this manuscript, the comparative parametric study of two similar sets of evacuated tube solar air heater (ETSAH) is performed. The comparison is based on energy & exergy analyses, and also presents the environmental and economic study (4E analyses). Each set is fabricated using mild steel (M.S.) along with 50 evacuated tubes with total collector area of 8.46 m2. The experimental investigations are made at diverse flow rates, with and without using conventional reflectors. Without incorporating any additional heat storage unit, the system provides average hot air temperature of 76.13°C when average solar intensity was 502.68 W/m2 during 11 h of operation from 09:00 to 20:00 h. ETC's absorber glass and the M.S. material was observed to have significant energy storage and discharge. The single set of ETSAH has mitigation of 89.20 tons with 2.05 years of energy payback period, which is significantly low as compared to its 20 years of lifespan. For the optimum system performance the cost of generated hot air is 0.00048 $/kg, which is considerably low.