LOW-COST HIGH-ACCURACY PARABOLIC TROUGHS CONSTRUCTION AND EVALUATION

This paper describes a low cost method for mass-production of paraboli c surfaces with fibreglass. Cavities produced with plastic conduits, c overed with fibreglass at the back of the collector surface, provide r einforcement in the longitudinal and transverse directions, to increas e rigidity. This produces a low-cost high-rigidity structure that is a n accurate copy of the mould. The accuracy of the parabolic surface de pends on the accuracy of the mould. The details of the mould productio n and the procedure for producing the parabolic surface are presented. The total thickness of the fibreglass is 4mm (mean value). The inside surface where the reflector is fixed is manufactured to a high degree of surface finish. The cost of the surface is US$ 30 per square metre of aperture area for 90 degrees rim angle. The standard deviation of the distribution of the parabolic surface errors is found equal to 4.7 mrad which indicates a very accurate surface. The deflection of the s urface to a force corresponding to a wind velocity of 90 MPH is well w ithin reasonable limits.