Design, optimization and optical performance study of tripod heliostat for solar power tower plant

Heliostats account for about 50% of the capital cost of power towers. In conventional heliostats with vertical pedestals and azimuth-elevation drives, the support structure contributes 40-50% of this cost due to heavy cantilever arms required by the large spanning structures. Additional costs are imposed by costly, difficult to maintain drive mechanisms. Here we show that a tripod heliostat can substantially address these shortcomings. We have presented the protocol and results of systematic structural analysis of heliostats with aperture areas of 62 and 100 m(2). We have included effects of shape on load reaction and structure cost. An in-house ray-tracing software is incorporated to estimate the performance penalties due to deformation under gravity and wind loads. The analysis shows that the additional energy collection by a less-stiff, larger heliostat more than offsets the spillage due to the greater deformation of the same. We have demonstrated that the economics of power towers are strongly governed by the structural cost of the heliostats rather than by their optical performance. We have brought down the cost of a tripod heliostat to $ 72/m(2) which is less than half that of the conventional systems and meets the target set by the US National Academy of Engineering. (C) 2017 Elsevier Ltd. All rights reserved

Thermal hydraulics of natural circulation loop in beam-down solar power tower

There have been continuous efforts by researchers and power producing companies to reduce various costs involved in solar power tower (SPT) plants. Economically deploying conventional SPT plants for industries using thermal or thermo-chemical processes which need temperatures >1100 K could be challenging. Here, the overall economics of deployment of conventional SPT could go unfair as such design needs larger heliostat field, therefore costlier stiffer heliostats to reach high concentration ratio (CR). These challenges can be solved by beam-down SPT which uses secondary reflector mounted on tower top and receiver cum secondary concentrator on the ground could achieve desired CR, is one potential candidate to save on tower construction and pumping costs. Using beam-down SPT heat can be made available at the ground which opens an option of extracting the heat using natural circulation loop (NCL). The current paper explores the new proposed configuration of NCL in terms of understanding thermal hydraulics using 3-D CFD simulations. Further, it also incorporates optimization of the proposed design configuration using formulated heat transfer model. The optimized geometry is simulated using 3-D CFD simulation which gave the desired rating. (C) 2018 Elsevier Ltd. All rights reserved