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Generating electric power using solar thermal systems is effective, particularly for countries with high solar potential. In order to decide on a relevant location to implement the solar tower plant and develop the mathematical model of a no-blocking heliostat field, a meteorological assessment was discussed in this paper. In addition, a parametric study was examined to evaluate the effect of the designed parameters (heliostat size, heliostat height from the ground, tower height, receiver aperture, and the minimum radius) on the solar field's performance. The preliminary solar field was then compared to the final design using the optimal design parameters. The obtained results showed that "Tamanrasset City" satisfied the necessary conditions for implementing a solar tower plant. According to preliminary solar field generation, no heliostat blocked its neighbor with a blocking efficiency of 100%. An analysis of its performance revealed that the optimized solar field would be capable of producing 15, 6571 MW, operating at an optical efficiency of 76.95%, and the enhancement rate of both efficiency and power output was 8.1%. [ABSTRACT FROM AUTHOR]

An important part of future global energy depends on the development of the solar industry. To date, we have noticed the shift from fossil fuels energy towards renewable energy. The past decade has shown significant progress in computer science and CAD is increasingly used for design and development. Visualization of the data generated from the models in the CAD program plays an important role in the creation of state-of-the-art designs. An important limitation during the design phase is the visualization of three-dimensional geometry. This article attempts to illustrate the use of VR technologies in solar thermal power plant development. This article analyzes various strategies and methods for the visualization of CAD models in virtual reality. Android phone interfaces with a desktop computer, as well as head movement control strategies, are discussed. It is concluded that VR technologies can help with visualization, as well as in the development of the field of solar thermal power plants, having minimal design-related issues. [ABSTRACT FROM AUTHOR]

Heliostat tracking is a critical component of the solar field of concentrating solar power tower (SPT) systems and can be the source of significant losses in power and profit when it lacks the necessary accuracy. This paper presents an advanced heliostat drive system for the SPT generation plant. An integrated model for the heliostat drive system based on dual axes tracking is proposed using an inexpensive angle sensor. The mathematical model of the integrated drive system is developed, including the solar, tower, and heliostat models. The matlab simulation model for the proposed integrated drive system is developed and evaluated. An experimental prototype for a dual-axis heliostat is built using Class-E direct current choppers and an inexpensive Gyro angle sensor. The prototype is tested and considered in the Dhahran region in Saudi Arabia under different operating conditions. A comparative study between simulation and experimental results is conducted to assess the efficacy and accuracy of the proposed controller drive system and validate the developed integrated model. Both simulation and experimental results demonstrate the effectiveness of the proposed dual-axis trackers to follow the sunbeams throughout the year. [ABSTRACT FROM AUTHOR]

This study presents an analysis of the theoretical upper limits to the mean annual optical efficiency of the Light Collection and Concentration (LCC) subsystem of a solar tower system, which is the subsystem composed of the heliostat field and the active surfaces of the receiver that capture the concentrated solar radiation sent by the heliostat field to transform it into thermal energy. The "ideal" LCC subsystem is modelled gradually, by incrementally introducing into the model factors that limit the mean annual optical efficiency of any LCC subsystem and whose influence in the optical efficiency cannot be reduced to zero, starting with the cosine factor, followed by the atmospheric transmittance, and then by the product of the receiver intercept factor and a factor related to the shading of the heliostat field by the receiver. At each degree of complexity of the ideal LCC subsystem model, the optimal configuration of the "ideal" LCC subsystem that achieves the highest mean annual optical efficiency in terms of heliostat field shape and receiver size is identified for a selected range of latitudes, tower heights and heliostat field sizes or total mirror areas. Thus, the upper-limits of the mean annual optical efficiency of the LCC subsystem of solar towers are obtained as a function of the specified parameters. The results obtained show that at a latitude of 30° North, for tower heights between 200 and 300 meters and heliostat fields with mirror areas between 1.3 km2 and 2.5 km2, the upper limit of the mean annual optical efficiencies vary between 79.2% and 74.7%, with the highest upper limit corresponding to the combinations of the tallest towers and smallest heliostat fields. This strongly indicates that the mean annual optical efficiency of actual solar mono-tower systems of commercially realistic heliostat field sizes and tower heights will hardly reach 70% at any location on Earth. • Upper limits as a function of optical factors. • Factors considered: Cosine, Transmittance, Receiver Intercept and Shading. • Influence of latitude, field and receiver size and tower height on upper limits. [ABSTRACT FROM AUTHOR]

Solar central receivers have inherently large time constants and time delays caused by their thermal inertia are due to the transport of the heat transfer fluid alongside the panels. This problem is even accentuated if these systems are continuously exposed to direct normal irradiance (DNI) fluctuations. Ensuring an adequate operation of this kind of process implies the adaptation of control strategies. This paper proposes a strategy that couples the temperature control of the outlet fluid while considering the heliostats' aiming points location to maintain the receiver operating below its design limit and simulates its performance under several scenarios. These tests are carried out on a non-steady-state solar plant model that considers its optical and thermal characteristics. The structure of the proposed control system is based on using intermediate flow valves along the heating flow path to reduce time delay. Hence, it renders the control system more responsive to either a DNI variation affecting the solar field or moving its operation from one state to another. The control strategy structure contains feedback and feedforward loops to determine the near-future process response to DNI measurements. It allows adding more information to the loop used to maintain the system's desired steady-state operation. The overall strategy can take the process to a steady-state operation regardless of the hour or day of operation. It produces a low variation of the outlet temperature, with a standard deviation of 3 °C, while the receiver is under a transient DNI and maintains the heliostats aimed toward the receiver without exceeding its heat flux limits. Results indicate that the proposed strategy achieves over 80% improvement based on the integral absolute error (IAE) performance index compared to conventional single-loop temperature control. Besides the simulated numerical results, this research also presents the advantages of considering intermediate mass-flow valves for control purposes of the receiver. This work should be considered a step towards improving multivariable control algorithms for the safe operation of solar central receivers. [ABSTRACT FROM AUTHOR]

Summary: The trend of global environmental pollution underscores the design and application of technologies capable of operating with clean energy sources such as solar energy. Toward this, the current study presents a novel design of combined cooling, heating, and power production system that utilizes a solar‐based heliostat technology with thermal energy storage in combination with a modified Kalina cycle. This cycle has been improved by the smart use of multi‐heat recovery method and the employment of an ejector. The performance of this system has been studied in three solar radiation modes, including solar mode (solar radiation in the early and late time of a day), solar and storage mode (solar radiation in the middle of a day), and storage mode (night time). This study is based on the development of a fully validated numerical modeling for these three modes and the use of a parametric study including the effect of several important parameter changes on generated electricity, power to cooling and heating ratios, and energy and exergy efficiencies (electrical and overall). The results show, the net generate electricity of the system in the solar mode, solar and storage mode, and storage mode was 3086, 1891, and 1668 kW, respectively. The electrical energy efficiency for the mentioned modes was 15.81%, 5.38%, and 7.84%, and also the electrical exergy efficiency was 6.56%, 2.81%, and 4.14%, respectively. Finally, the overall energy efficiency for these modes was 66.7%, 39.4%, and 63.9%, and the overall exergy efficiency was 8.95%, 4.86%, and 7.50%, individually. [ABSTRACT FROM AUTHOR]

Summary: The present study focuses on the optimization of solar tower power plant heliostat field by considering different heliostat shapes including rectangular, square, pentagon, hexagon, heptagon, octagon, and circular heliostat shapes. The optimization is carried out using an in‐house developed code‐based MATLAB program. The developed in‐house code is validated first on a well‐known PS10 Solar Thermal Power plant having rectangular heliostats shape and the resulting yearly unweighted heliostat field efficiency of about 64.43% could be obtained. The optimized PS10 heliostat field using different heliostat shapes showed that the circular and octagon heliostat shapes provide better efficiency with minimum land area. The yearly efficiency is increased from 69.65% for the rectangular heliostat shape to 70.96% and 71% for the octagon and circular shapes, respectively. In addition, the calculated field area (land area) is reduced for the case of circular and octagon heliostat shapes with a gain of about 11.10% and 10.93% (about 42.0436 × 103 and 41.4036 × 103 m2), respectively, in comparison with the PS10 field area. [ABSTRACT FROM AUTHOR]

Summary: The present study focuses on the optimization of solar tower power plant heliostat field by considering different heliostat shapes including rectangular, square, pentagon, hexagon, heptagon, octagon, and circular heliostat shapes. The optimization is carried out using an in‐house developed code‐based MATLAB program. The developed in‐house code is validated first on a well‐known PS10 Solar Thermal Power plant having rectangular heliostats shape and the resulting yearly unweighted heliostat field efficiency of about 64.43% could be obtained. The optimized PS10 heliostat field using different heliostat shapes showed that the circular and octagon heliostat shapes provide better efficiency with minimum land area. The yearly efficiency is increased from 69.65% for the rectangular heliostat shape to 70.96% and 71% for the octagon and circular shapes, respectively. In addition, the calculated field area (land area) is reduced for the case of circular and octagon heliostat shapes with a gain of about 11.10% and 10.93% (about 42.0436 × 103 and 41.4036 × 103 m2), respectively, in comparison with the PS10 field area. [ABSTRACT FROM AUTHOR]

• The fast pyrolysis of biomass in a fluidized bed reactor using solar energy was analyzed. • A biomimetic mini heliostat field was optimized to provide the required thermal energy. • The inert gas was heated in a tubular thermal receiver to provide thermal energy. Biofuels may significantly influence the world's transition from hydrocarbons to renewable energies. Pyrolysis uses thermal energy in an anaerobic ambiance to crack biomass and create biofuels (bio-oil and synthesis gas). This work reports a detailed computational study of a novel system to develop fast biomass pyrolysis with concentrated solar energy. A fluidized bed reactor was coupled to a solar thermal receiver to heat the inert fluid (nitrogen) using a biomimetic mini heliostat field which provides the required thermal energy. A detailed kinetic model for the pyrolysis of lignocellulosic biomass was solved simultaneously with a set of differential equations based on mass, momentum, and energy conservation principles. An Eulerian-Eulerian approach was considered with three phases. The computational model was compared with data reported in the literature for the fluidized bed reactor and heat transfer in the solar thermal receiver with good agreement. Concentrated solar fluxes on the receiver, nitrogen outlet temperatures, temperature contours inside the reactor, concentration contours of relevant gases, and global product percentages (Tar, Char, and Gas) are reported. The products reach an almost constant composition of Gas, Tar, and Char after 6 s of reaction, indicating the annual operational stability of the solar pyrolysis plant in terms of biofuel production. [ABSTRACT FROM AUTHOR]

Summary: Heliostat field or solar tower collector is one of the most promising concentrated solar power technologies available in the market. Due to its high operating temperature, heliostat field collector can be implemented in a wide range of applications from solar power generation to industrial commodity production. There are several currently operating, under construction, and planned heliostat fields around the world. In this paper, a brief overview of the current state of the art, applications, assessment methods, future perspective, and methods of improvement are discussed. [ABSTRACT FROM AUTHOR]

In India, the desert regions of Rajasthan and Gujarat are preferred for installation of solar photovoltaic (PV) and concentrated solar thermal (CST) systems because of a high level of both DNI and GHI components of solar radiation. However, such regions pose substantial challenges in terms of dust, a high ambient temperature and scarcity of water. This paper is an attempt to address issues related to the deposition of dust (a) on a mirror with stand depicting PV panel or heliostat in the wake of a similar geometry and (b) in the porous absorber of an open volumetric air receiver (OVAR). A detailed insight to the wake-region behind an inclined flat-plate or heliostat is provided based on analysis and experiment. These indicate possible measures such as modification of the geometry of collectors to mitigate the problem of dust deposition. Also, the use of a cyclone separator with defined parameters based on a decision variable has been suggested for reliable operation of an OVAR. These problems being generic in nature, similar strategies are expected to be applicable in other desert regions subject to their specific conditions. [ABSTRACT FROM AUTHOR]

A comprehensive study of the latitude-orientated configuration of non-imaging focusing heliostat (LO-NIFH) is reported. In this configuration, we have made the sun tracking formulas of a non-imaging focusing heliostat (NIFH) to be independent of the latitude where it is installed; hence we name it a latitude oriented non-imaging focusing heliostat or LO-NIFH. With the new configuration, the LO-NIFH introduces certain potential advantages in field applications; such as offering a standard in mechanical/optical designs, simplifying the mechatronic control schemes, offering high modularity and high scalability in both production and project implementation. One of the most important merits of latitude oriented configuration is that it makes a heliostat operating at a very narrow range of incident angles in a day; for instance, incident angles ranging from 0° to 52° for 14 h of tracking time per day. When a NIFH tracks the sun at a moderately small incident angle, it always makes a reasonably small focused spot (at the target) with a high optical efficiency above 88% at a f / D ratio of greater than 1. For an off-axis solar concentrator, such level of optical efficiency is considered very impressive as it is just 10% less than that of on-axis parabolic dish. We found that the astigmatic spread of a working LO-NIFH has little variation with time as compared to that of a spherical reflector operating in off-axis manner. Computer simulation of the focused spot images was conducted and compared with the spot images photographed at the site of a prototype LO-NIFH with an array of 5 × 5 mirror facets tracking at an incident angle of 23°. [ABSTRACT FROM AUTHOR]

We assess the storage capacity of a solar thermal plant needed to achieve a given probability of avoiding an unscheduled reduction in output throughout the year, due to the variability of the solar resource. To our knowledge, this is the first time such an assessment has been reported. The majority of cases are assessed for the reference case of a constant output at full load, although a limited assessment of the influence of turn-down is also reported. The model accounts for the diurnal, seasonal and weather-based variability of the solar resource by the use of ten-year historical time-series of direct normal irradiance. Calculations are performed using a simplified, in-house model of the solar thermal plant that assumes stead-state at each hourly time-step. The reference conditions are selected to be best case-efficiencies for plant sub-systems. Sensitivity analyses are used to assess the influence of reduced device efficiency and of the size of the power-block relative to the heliostat field. The current analysis is independent of the type of storage, so that it assesses the quantity of storage required regardless whether it is sensible, chemical, or latent. Calculations are performed for six sites, three in the USA and three in Australia, all with an excellent solar resource. The results find that typically four to ten days of storage, together with a power-block size an order of magnitude lower than that of the maximum heliostat capacity, is required to achieve a probability of avoiding an unscheduled reduction in output from the maximum of less than one day every three years. However, the storage capacity can be reduced by a factor of five if it is acceptable to turn the output down to 40% of the maximum value. Assessments of utilisation factors and dumping energy when storage capacity is reached and solar efficiency provide further insight into these findings. [ABSTRACT FROM AUTHOR]

Solar thermal power generation is based on the concept of concentrating solar radiation to provide high temperature heat for electricity generation via conventional power cycles. The high relative cost of optical subsystems necessitates a careful study of their components. Solar collector fields are typically modeled by ray-tracing or convolution methods; however, no general method is available for engineering analysis. We propose the use of caustics to predict the image of the sun reflected by an arbitrary mirror of focal length F and aperture a on a target. The mirror surface is described parametrically by a quadric and placed at a distance L from the target on a heliostat. The method of caustics was validated against SolTRACE, a ray-tracing code developed by U.S. National Renewable Energy Laboratories . We show that there is a value of aF which depends on aL, for which the incident average energy flux to the target reaches a maximum. The method of caustics allows the efficient computation of the image on an arbitrary target surface and obviates many of the difficulties with ray-tracing methods. [ABSTRACT FROM AUTHOR]

Abstract: The tracking and ray tracing equations for the target-aligned heliostat for solar tower power plants have been derived in this paper. Based on the equations, a new module for analysis of the target-aligned heliostat with an asymmetric surface has been developed and incorporated in the code HFLD. To validate the tracking and ray tracing equations, a target-aligned heliostat with a toroidal surface is designed and modeled. The image of the target-aligned heliostat is calculated by the modified code HFLD and compared with that calculated by the commercial software Zemax. It is shown that the calculated results coincide with each other very well. Therefore, the correctness of the tracking and ray tracing equations for the target-aligned heliostat is proved. [Copyright &y& Elsevier]

Abstract: Wind loads on heliostats are usually determined at boundary layer, low-speed wind tunnels, where the design full-scale Reynolds number cannot be reached. In doing so, it is supposed that the wind load coefficients are Reynolds number independent, which is known to be the case for sharp edged bodies. For the stow position the usually round torque tube is directly exposed to the wind and could influence the wind loads. By measurements in a high-pressure wind tunnel, it can be demonstrated that the design-relevant wind load coefficients are not Reynolds number dependent. However, the inclination of the mirror plane in stow position, due to the deflection of the heliostat’s structure at high Reynolds number, leads to increased wind loads and must be considered. The results are also valid for photovoltaic trackers of similar shape. [Copyright &y& Elsevier]

Abstract: In this article, a new tool is introduced for the purpose of locating sites in hillside terrain for central receiver solar thermal plants. Provided elevation data at a sufficient resolution, the tool is capable of evaluating the efficiency of a heliostat field at any site location. The tool also locates suitable sites based on efficiency and average annual normal insolation. The field efficiency, or ratio of radiation incident to the receiver to direct normal solar radiation, is maximized as a result of factors including projection losses and interference between heliostats, known respectively as cosine efficiency, shading, and blocking. By iteratively defining the receiver location and evaluating the corresponding site efficiency by sampling elevation data points from within the defined heliostat field boundary, efficiency can be mapped as a function of the receiver location. The case studies presented illustrate the use of the tool for two field configurations, both with ground-level receivers and hillside heliostat layouts. While both configurations provide acceptable efficiencies, results from case studies show that optimal sites for ground-level receivers are ones in which the receiver is at a higher elevation than the heliostat field. This result is intuitive from the perspective of minimizing cosine losses but is nevertheless a novel configuration. [Copyright &y& Elsevier]

Abstract: Deployment of the first generation of grid-connected plants for electricity production, based on Solar Thermal Power Plants with Central Receiver System technology using large heliostat fields and a solar receiver placed on the top of a tower, is currently being boosted by the first commercial plants in Spain, PS10, PS20, and Gemasolar. Therefore one of the main goals of solar technology research is the study of existing receivers and development of new designs to minimize heat losses. In this context, volumetric receivers appear to be the best alternative to tube receivers, mainly due to their functionality and geometric configuration. They consist of a porous material that absorbs concentrated radiation inside the volume of a structure and transfers the absorbed heat to a fluid passing through the structure. Solar radiation is first converted into thermal energy or chemical potential, and then at a later stage, into electricity. This volumetric receiver technology has been under development since the early 1990s in various research and development projects. This paper is a chronological review of the volumetric receivers of most interest for electricity production, identifying their different configurations, materials and real and expected results, and pointing out their main advantages and conclusions based on the multitude of international and national projects reports and references. This study also deals with other important issues surrounding the volumetric receiver, such as the basic plant configuration, flow stability phenomenon and the main problems of a windowed design for pressurized receivers. [Copyright &y& Elsevier]

Abstract: This study of concentrating solar thermal power generation sets out to evaluate the main existing collection technologies using the framework of the Analytical Hierarchy Process (AHP). It encompasses parabolic troughs, heliostat fields, linear Fresnel reflectors, parabolic dishes, compound parabolic concentrators and linear Fresnel lenses. These technologies are compared based on technical, economic and environmental criteria. Within these three categories, numerous sub-criteria are identified; similarly sub-alternatives are considered for each technology. A literature review, thermodynamic calculations and an expert workshop have been used to arrive at quantitative and qualitative assessments. The methodology is applied principally to a case study in Gujarat in north-west India, though case studies based on the Sahara Desert, Southern Spain and California are included for comparison. A sensitivity analysis is carried out for Gujarat. The study concludes that the linear Fresnel lens with a secondary compound parabolic collector, or the parabolic dish reflector, is the preferred technology for north-west India. [ABSTRACT FROM AUTHOR]

Abstract: A 4m×4m toroidal heliostat with receiver oriented dual-axis tracking, also called spinning-elevation tracking, was developed as an auxiliary heat source for a hydrogen production system. A series of spinning-elevation tracking formulas have been derived for this heliostat. This included basic tracking formulas, a formula for the elevation angle for heliostat with a mirror-pivot offset, and a more general formula for the biased elevation angle. This paper presents the new tracking formulas in detail and analyzes the accuracy of applying a simplifying approximation. The numerical results show these receiver oriented dual-axis tracking formula approximations are accurate to within 2.5×10−6 m in image plane. Some practical tracking strategies are discussed briefly. Solar images from the toroidal heliostat at selected times are also presented. [Copyright &y& Elsevier]

Abstract: Knowledge of the mean reflectance of solar thermal central receiver system heliostat fields is highly relevant for both operation and component evaluation. Calculation of the mean reflectance becomes essential to establishing a procedure by which its value can be found without measuring each and every one of the facets that make up the field, since this is a long, time-consuming and not very productive task. This article reports on the results of a statistical reflectance study of the Plataforma Solar de Almería Central Receiver Systems (CRS) heliostats field. [Copyright &y& Elsevier]

Abstract: When striving for maximum efficiencies in solar thermal central receiver systems (CRS) the use of gas turbines with bottoming cycles is inevitable. Pressurized volumetric receivers have proven their feasibility and good performance, and their integration into gas turbine cycles has been demonstrated. One disadvantage of this system is the necessity to use secondary concentrators. The sunlight has to be concentrated into the relatively small glass windows of the receiver, which leads to a limited view cone. This means that of all the possible heliostat positions around the tower, only those within the ellipse, resulting from the section boundary of the view cone with the ground plane, are usable. For small systems, for which tower costs are small, the resulting heliostat field layout is similar, with or without secondary concentrator. For large systems, which are more cost-effective, tower costs become significant, and the losses due to atmospheric attenuation and spillage dominate over the cosine losses. Thus, the purely North-oriented fields become increasingly sub-optimal. This article shall demonstrate at what power levels this problem can be alleviated by not using a single, North-oriented aperture, but up to six apertures—each of them associated with a separate heliostat field. [Copyright &y& Elsevier]

Instead of using a specific focusing geometry, a non-imaging focusing heliostat has no fixed geometry but is composed of many small movable element mirrors that can be manoeuvred to eliminate the first-order aberration. Following our previous publication on the principle of non-imaging focusing heliostat, this paper further explores higher order residual aberration that limits the size of the focusing spot. The residual aberration can be partially corrected by offsetting the pivot point of mirrors and pre-setting the tilting angles of mirrors. [Copyright &y& Elsevier]

Investigates thee role of flux density in the design and operation of molten-salt solar central receivers. Identification of the insolation status of heliostat; Impact of illuminated heliostats on flux density; Function of heliostat field.