Design of Solar Heliostat System for a Community Level Cooking Application

Community level cooking is one of the energy intense cooking application, for which the input energy is conventionally obtained through LPG, electricity etc. For instance, a typical community cooking setup at BITS, Pilani-Hyderabad, India catering 1200 people requires about 135 Kg/day of LPG(~6195.84 MJ), costing around $215/day, there by emphasizing the need to go for better alternatives. Solar heliostat systems (SHS), which could be one the possible alternatives for such applications, employ mirrors to concentrate solar energy at a specified point. This paper demonstrates the undertaken attempt to design a SHS for a community cooking application at BITS, Pilani-Hyderabad, India (17.55°N, 78.55°E), which requires steam for cooking. The design algorithm incorporates pertinent mathematical models for designing the heliostat fields and the solar radiation data of a location in India. The design adopts a radial staggered configuration with the inputs being location co-ordinates, mirror reflectivity, time of day, month number, inlet & exit enthalpy of water, desired steam conditions, mirror dimensions etc. The number of mirrors required was ascertained by knowing the energy required to be concentrated by the heliostat field, available solar radiation, cosine efficiency, atmospheric attenuation etc. Using custom developed software, co-ordinates of each mirror on the field along with its spatial orientation, expressed in terms of azimuth and elevation angles, were determined. Salient parametric values obtained to generate steam of 25 kg at 2 bars, 200°C are: mirror area=1m²; reflectivity of mirror=0.86; the maximum angular distribution of the heliostat field from north axis=35°; minimum number of mirrors=108; coordinates of the mirrors vary from (0, 20) to (-8.255, 34.09); length of receiver=1m; height of tower=20m. The design also gives the azimuth and elevation angles for different mirrors which may be used for designing the proper tracking system.