Publications
Development and Validation of the Passive Adjustment Toroidal Heliostat (PATH™)
by Alex Lehmann
High solar field efficiency is an important goal for improving the cost effectiveness and practicality of point focus solar thermal systems. Simulations performed by Heliosystems have shown that very significant improvements can be made to the energy capture efficiency of solar thermal receivers by improving the concentration ratio of the solar field. These improvements are beyond the capability of conventional heliostats and a new type of heliostat is required. Heliosystems has developed the first prototypes of a new heliostat called a Passive Adjustment Toroidal Heliostat (PATH™) to meet these requirements. The performance of the PATH™ is compared with toroidal and other conventional spherical azimuth-elevation heliostats
Rapid Heliostat Surface Measurement Using Reconstruction From Camera Images
by Alex Lehmann
The modelling of a solar concentrator is central to its design, operation and evaluation. Increasing sophistication in modelling requires more detailed information about the nature of the concentrator to predict its performance accurately. In particular, the profile of an image from a heliostat is important for understanding and predicting the energy that can be collected at a receiver. As the heliostat image is a direct result of its curvature, the only way of universally characterizing this image is by measurement of the heliostat reflector curvature itself. Conventional surface measurement techniques cannot be applied to large heliostat mirrors at mass production scale because of cost, practicality and accuracy limitations. This study demonstrates how the curvature of a heliostat can be calculated from two digital camera photos of the reflector surface. The setup is inexpensive and can be easily implemented in a heliostat assembly line.
Focal Length and Field Optimisation for Toroidal Heliostats in High Accuracy Solar Concentrators
by Alex Lehmann
A toroidal heliostat including mount and tracking system has been engineered for cheap large scale production. The heliostats are supported by a toolbox of complex simulation and optimisation interfaces used for the implementation of the heliostats in solar concentrator fields. The interfaces are required for optimisation of the heliostat focal lengths right through to generation and simulation of full solar fields for any given set of thermal receiver parameters. Full heliostat field simulation results have shown that toroidal heliostats perform significantly better than spherical heliostats, and empirical relationships have been developed to help the rapid identification of optimal field, heliostat and aperture configurations.
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