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

Technoeconomic analysis of biogas production using simple and effective mechanistic model calibrated with biomethanation potential experiments of water lettuce (pistia stratiotes) inoculated by buffalo dung

While many papers report biomethanation potential of various substrates subjected to various treatments, very few report the economic implications of their work. Here, we report a simple but effective mechanistic model, using Contois and Monod kinetics, considering only two classes of micro-organisms (a) acidogens and (b) acetomethanogens. We fitted our model to CH4 and CO2 evolution data from biomethanation studies of water lettuce (pistia stratiotes) inoculated with buffalo dung at five different ratios of substrate to inoculum. The data was obtained by gas chromatography. The model has been used to simulate three types of biodigestors: (a) 1-stage continuous digestor, (b) 2-stage continuous digestor and (c) semi-batch digestor with intermittent draining of digestate. The 2-stage digestor exhibited no major improvement over the 1-stage digestor presenting only a 4% increase in methane production rate with 25% longer response times. The best performance was shown by the semi-batch operation due to tolerance of high microbial loads. Biogas generated from water lettuce grown on a farm pond and using the semi-batch approach can be monetized by offsetting use of market bought LPG. The return on investment is 24.7% and 25 kg of CO2 emissions are abated per ton of water lettuce utilized