The rate of solar AR-M 1896 reflected by the internal reflector and absorbed by the water (qw−int) and by the absorber (qb−int) is given as:equation(303)qw−int=I(t)drτgρintαwlbtanθcosφtan?equation(304)qb−int=αbαw(qw−intτw)
From the numerical simulation of the active still, it was observed that the addition of reflectors improved the daily production of the still about 127.06% in winter, 21.78% in spring and 10.1% in summer. Also the coupling of the still with a thermal storage tank led to an increase of the production rate equal to 17.36%, 28.34% and 33% respectively for winter, spring and summer. The daily production rate of the still coupled with the photovoltaic/thermal system was about 47.61% in winter, 137.5% in spring and 131.06% in summer. It was concluded that the effect of the reflectors on the increase of the daily production of the still is very significant during the period of winter compared to the spring and summer but on the other hand, the storage tank is far more important in spring and summer in comparison with winter.