Present study is the offshoot of a successful project (to recover usable water from dye-wastes) in our intuitively designed 4-roof, flared-wall single-basin solar still. That work evoked curiosity to thoroughly explore the fundamentals of the currently used traditional solar stills.
First: Single-basin regular stills of 1 or 2-roof designs incorporate triangular side-walls and/or back-wall of large areas introducing energy wastage and efficiency reduction; necessitate cumbersome orientation along N-S directions and adjustment; wall-areas/cavity volumes become unwieldy for higher roof-angles. These undesired aspects are eliminated in 4-wall design, while roof-area remains the same.
Second: For incident angles above 50 deg of sun's rays on a glass surface, Sears curve predicts exponential increase in glass-air reflection loss (from 4%). Sun-angle calculations showed a 30 deg roof-angle as acceptable for all latitudes (including equator) during all seasons, contradicting age-long dictum that roof-angle is latitude-dependent.
Third: Geometric considerations show shadowing above 40% of basin area during early and late hours. Flaring of basin-walls to 170 deg augments collection efficiency.
Fourth: Published data suggest a 1” basin water-level as desirable. In a still with 2” high basin-wall, larger unfilled wall-area dissipates heat. In 170 deg flared-wall case, water is filled above 1 ½”; horizontal glass partition is snug-fitted just above, along the perimeter, to simulate greenhouse. Larger flared-wall areas fully utilized, while water volume is only 50% of straight-wall case, thus increasing heating rate; glass-roof remains cooler, thereby enhancing condensation.
Fifth: To have ample cavity volume to maintain desirable vapor pressure, 35 deg roof-angle is selected.
RESULT: In-depth analysis incorporating novel ideas yields the best design for innovative, universal solar still: 4-roof, 35deg slant angle, single-basin with 170 deg flared-walls, horizontal glass partition to simulate greenhouse, reducing glass temperature.
(1) This work involves innovation in design concepts negating the routine manufacturing techniques.
(2)&(3) Cost of materials and manufacturing will almost be similar, while the installation difficulties will diminish. This is also scalable to treat large volumes of waste water and is universally adoptable.
(4) Marketability will be high because of increase in overall recovery of water. Many homes in countries like India use salty/bore-well water and face extreme scarcity of potable and hygienic water even for a small family of 2-3 persons. This device will be of extreme use.
(5) This 4-roof concept developed here based on optical considerations can be used in all the passive solar devices such as solar panels which need robust support structures (to withstand wind and snow loads) so that these panels can be safely kept tilted at the latitude-angle. If we replace the flat glass top of the passive solar systems by our 4-roof design even with lower tilt, the expenses incurred in support structures will be eliminated. The annual collection efficiency will substantially increase at any latitude.
(6) This innovative concept will revolutionize the design of whole spectrum of solar passive devices.
ABOUT THE ENTRANT
Name: Mukilan Suresh
Type of entry: individual
Patent status: none