Water mass in the evacuated tubes:equation(243)AtNtcI(t)Cη0−a′AtNtc(Twc−Ta)=MwcCwdTwcdt+Ntcm?Cw(Twc−Tw)where a′ is the solar collector efficiency coefficient.
Water mass of the solar still:equation(244)Ntcm?Cw(Twc−Tw)+αw′AbI(t)s+hwAb(Tb−Tw)=ht,w−gAb(Tw−Tgi)+MwCwdTwdt
On the basis of the study, it was found that the maximum daily BIM 23056 and exergy efficiencies were about 33.0 % and 2.5%, respectively, and the maximum daily yield was found to be 3.8 kg/m2 for 0.03 m basin water depth. Also the evaporative fractional exergy dominates over the radiative and convective fractions at most of the time. To make the system efficient, protostomes was suggested that smaller size of ETC with ten number of tubes is preferable than a single unit the larger size ETC integrated.
7.2.3. Concentrator collector
Singh et al.  developed analytical expressions for the water temperature of an active solar distillation unit with flat plate and concentrator collectors in terms of system and climatic parameters. The schematic diagrams of the solar still with a flat plate collector and with a concentrator are shown in Fig. 29 and Fig. 30, respectively. The solar still was placed at a higher position than the collector or concentrator to create sufficient pressure for thermosyphon flow.