CPV, CSP solar

CSP Ganged Heliostat Technologies
Investigations in a Tensile Based Non-imaging System
Abstract:
Background
Concentrating Solar Power (CSP) and specifically Power Tower or Beam Down type systems achieve high levels of solar concentration and efficiency. Collecting fields comprise a large fraction of the system installation and maintenance costs. Technological advances promise economically competitive solar power. Skysun, LLC proposes a ganged heliostat to significantly reduce these costs.
Method
Typically, a heliostat requires one each of the following: mirror module, support structure, dual axis drive, post/pedestal and foundation. Each of Skysun, LLC’s heliostats require: mirror module, reduced support structure and a single axis drive, eliminating the need for a pedestal and foundation for each heliostat. The ganged heliostat consists of two cables supporting a plurality of single-axis actuated heliostats. The cables act both as a supporting structure and as a translator of focusing motions to the many heliostats. The cables terminate to an actuated rotational member supported by a substantial post. Cable tension may be variable. This configuration reduces the ratio of posts and foundations to heliostats, and eliminates dual axis drive actuators, substituting single axis actuators instead. The ganged heliostat may be rotated to the vertical for ease of robotic cleaning and water reclamation. The ganged heliostat may also be inverted, with the reflective surface downward, to protect against weather events such as hail. Finally, the ganged heliostat may be secured to protect against high wind conditions.
The reflective surface, which can be deformed by cable and heliostat orientation, provides an efficient means to form a large concave collecting surface laying principally in the horizontal. Reflected incident rays, being non-normal, suffer from astigmatism. Novel deformations of the reflective surface eliminate astigmatic aberration. A toric - shaped deformation of the reflective surface reduces the size of a chosen astigmatic focus, yielding higher concentration. Latitudinal and longitudinal deformations maintain focus upon a fixed receiver. In the ideal, the astigmatic focus is reduced to a point.
Conclusion
The goal of this paper is to outline the relatively inexpensive methods utilized by Skysun’s ganged heliostat prototype and how the methodology may be scaled up. Skysun, LLC proposes a ganged heliostat to significantly reduce collecting field costs to $75/m2 installed.
Key words: solar concentrating CSP Power Tower Beam Down heliostat astigmatism deformation ganged

The concentrated solar power industry requires high-temperature receivers to push towards advanced power cycles. However, as the outlet temperature of a receiver increases, radiation losses (which are ∝ 4) become dominant. In addition, at high temperatures, not many liquid working fluids are suitable. To address these issues, this research proposes an innovative, robust design of a gas-phase cavity receiver which utilises semi-transparent spheres as a volumetric absorption medium. The motivation behind this design is to break the long-standing outlet temperature versus efficiency trade-off by maximising the "volumetric effect" (i.e. obtaining a higher outlet fluid temperature than the receiver's surface temperature). A range of designs were compared (i.e. packed beds of semi-transparent and high-transparency quartz spheres against an opaque bed of ceramic spheres). This study is important because it determines how the volumetric effect modifies the overall receiver efficiency via a holistic metric (proposed herein) which accounts for the optical, thermal, and pumping power efficiencies. Through a detailed ray-tracing analysis and a comprehensive thermal circuit model, this study reveals that a semi-transparent quartz packed bed receiver can have an overall receiver efficiency of around 80 % at outlet temperatures above 700°C. Most significantly, the best proposed design achieved a high value for the elusive volumetric effect (e.g. a maximum index value of 1.45). Based upon these results, the authors can conclude that these packed bed designs represent a promising new pathway towards reliable and cost-effective high-temperature and high-efficiency receivers which can be implemented into advanced, high-temperature power cycles.

This paper deals with Hassi R’mel’s solar power plant, a solar power plant one (SPPI) located in Algeria’s southern region. The current configuration of the SPPI is a 25MW parabolic trough used with 130MW connected cycle gas turbines. In this paper, a techno-economic analysis of the solar part of the SPPI is described. A multiobjective optimization process was carried out to find the most favorable conditions, the most suitable parameters, and the solar power plant’s optimum design configuration for better energy production in the future.We optimized the solar multiple, the fossil fill fraction of the backup system, and a full load of thermal storage system for the minimum levelized cost of electricity (LCOE) and the maximum capacity factor. The results showed that the lowest LCOE reached about 5.83 e/kWh for a solar multiple of 1.6. The optimumvalue of fossil fill fraction is 0.2, with a capacity factor of 60%, and the best optimization of the storage system is 4 h. The optimum power plant produced 118.26GWh per year. It was concluded that the use of wet cooling was more economical than dry cooling and that among the heat transfer fluids, Therminol VP1 was the best. The validation of the theoretical results confirmed their agreement with the SPPI and solar energy generation system-VI power plants’ experimental data. These findings proved that concentrating solar power may be considered as the right solution in countries in the desert and equatorial regions, the Middle East and North Africa region, especially Algeria, where abundant solar energy is available.

Gas-phase solar receivers can operate over a wider temperature range than receivers which use conventional liquid heat transfer media. However, due to their relatively poor heat transfer performance, gas-phase receivers require substantially more heat transfer area and/or higher flow rates to extract the same amount of heat which leads to more complicated designs (e.g. a porous-media absorber with small feature/pore size) and decreased reliability (e.g. internal temperature gradients and higher thermal stresses). Detailed numerical modelling techniques can help elucidate the fundamental heat and mass transfer mechanisms/interactions in such to help mitigate these risks and to create innovative, high-performance, designs. To collate the research efforts towards gas-phase receiver modelling, this paper systematically reviews—and critically compares—the latest numerical studies of various high-temperature gas-phase receiver designs. It was found that, from a numerical point of view, gas-phase receivers can be categorised by whether they contain a porous medium or not. This categorisation is crucial, because it dictates the numerical techniques needed to capture the underlying phenomena. This review also found that no standardised performance metrics are reported for gas-phase receivers. We suggest that a holistic figure of merit, such as the one developed by Lenert et al. (Lenert et al. 2012), be adopted in this field to merge all performance criteria for comparative evaluation. Overall, the present review is expected to serve as a guide for the development/enhancement of receiver designs based on linking best practices in simulation/modelling with the key features and limitations of gas-phase receivers.

Solar Water Heating system is the most efficient and popular technology in the field of solar thermal energy harnessing. A comprehensive study of the Supply Chain Management (SCM) in solar water heating industry is being presented in this paper. The potential bottlenecks associated with major components of Supply Chain design viz. manufacturing, distribution, installation, operation and maintenance O&M have been addressed in order to meet the global deployment targets of green energy technology adoption.
Study reveals that most supply‐demand imbalances can be mitigated by implementation of action plan based on robust long term frameworks of secured demand, and constraints of costly raw materials can be resolved by switching to alternative more abundant materials such as composites, polymers etc. Certain components solely responsible for the performance of the SWH, hence required to be meet stringent quality standards without compromise, while other components may be considered as primarily cost-driven. Since the material used in SWH comply stringent quality standards, its economical recycling after completion of the codal life considered to be feasible as buy-back, hence scope of reverse supply chain is found worth to be exercised. Information technology in SCM has also been explained to ensure quality assurance, monitoring of proper disbursement of government subsidies, post selling services to end user etc. However the SWH technology is in mature stage, but due to absence of standardization, interchangeability and skilled manpower the results are not according to the efforts being made.
The bottlenecks have been assessed in light of extensive literature review and key recommendations have been made to support the decision makers in policy formulation.

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) sol-ver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to max-imise the performance of linear CSP reflector layout and receiver configurations.

"We have invented an electronic solar compass that can be used to determine with remarkable accuracy the direction of an observed point with respect to the true geographic North. This solar compass is patent pending RM2012A000664 (filed on 27th December, 2012).
The electronic solar compass is composed of an electro-optic sensor that detects the position of the sun, a GPS device that provides the Greenwich time and the coordinates of the compass, an optical pointer, a goniometer for measuring angles and a microprocessor, which elaborates the data and provides the angle of observation with respect to true North in real time. An innovative algorithm based on Kepler's laws allows determining the sun ephemeris and the North-South direction by knowing the local time and its geographic coordinates."
Link:  http://www.frascati.enea.it/fis/lac/excimer/bussola/

The Scenario Analysis methods have often been used by policy makers as an instrument to manage uncertainty and to support the shaping of long-term economy policies. In this research, we apply Scenario Analysis in order to identify the barriers affecting the decision to invest in the Concentrated Solar Power (CSP) sector in Morocco. Our results aim at facilitating the process of defining different paths in strategic political and policy actions. Using data from a survey on a panel of experts, the Cross Impact Analysis (CIA) and the Cross Impact Matrix System (SMIC) techniques are applied. The advantage of these techniques is that they allow including in the analysis the interlinkages between the events that will define the future scenarios. However, their limitation is that the number of events analyzed cannot be too high since the information collected from the experts increases exponentially according to the number of events introduced. We thus expand our analysis with a new methodological approach, combining the use of prospective and statistics techniques. This approach allows addressing the mentioned limitation and applying these techniques, initially restricted to 6 events in its common application, to a large number of events. The results show that uncertainty and informality would be key factors in promoting the arrival of companies in this sector. Additionally, regarding companies that already have a presence in Morocco's renewable energy sector, an increase in activity would be achieved through improvements in the easing of financial and legal barriers.