Central Receiver Research Articles

Improvement of heliostat pointing accuracy by calibration at optimized dissimilar source vectors

Almost all commercial heliostats are calibrated using the sun and a target placed below the central receiver. This setup limits the orientations that the heliostat can assume during calibration since the sun follows a restricted path. The calibration points, therefore, do not cover a wide range of heliostat orientations. This could lead to suboptimal calibration.This paper investigates the improvement in calibration that is possible when a heliostat’s orientation covers a wider range. In practice, this is possible by placing artificial light sources throughout the heliostat field.The investigation is done using only numerical simulations. Simulations make it possible to pinpoint the sources of poor pointing accuracy, which is difficult to achieve for physical heliostats.The results show that there is around a 10% improvement in pointing accuracy when using the alternative calibration method.

Potential Map for the Installation of Concentrated Solar Power Towers in Chile

This study aims to build a potential map for the installation of a central receiver concentrated solar power plant in Chile under the terms of the average net present cost of electricity generation during its lifetime. This is also called the levelized cost of electricity, which is a function of electricity production, capital costs, operational costs and financial parameters. The electricity production, capital and operational costs were defined as a function of the location through the Chilean territory. Solar resources and atmospheric conditions for each site were determined. A 130 MWe concentrated solar power plant was modeled to estimate annual electricity production for each site. The capital and operational costs were identified as a function of location. The electricity supplied by the power plant was tested, quantifying the potential of the solar resources, as well as technical and economic variables. The results reveal areas with great potential for the development of large-scale central receiver concentrated solar power plants, therefore accomplishing a low levelized cost of energy. The best zone is located among the Arica and Parinacota region and the northern part of the Coquimbo region, which shows an average cost of 89 USD/MWh, with a minimum of 76 USD/MWh near Copiapó.

Performance Evaluation of Multiple Helical Tubes as a Receiver for Solar Parabolic Trough Collector

Solar parabolic trough collector consists of a parabolic reflector with a central receiver at a focal point through which heat transfer fluid is passed. Parabolic trough collector is used mostly in solar thermal power plants for generating electricity. This paper describes the experimental results of two straight tubes wrapped over each other to form a helically shaped receiver. The receiver was tested with aluminium material with and without black paint over it. Also, the helical tube receiver was tested with a glass cover over it, at two different mass flow rates and, with and without manual tracking. The tested instantaneous thermal efficiency ranges from 31.26% to 45.28% and the overall thermal efficiency ranges from 14.9% to 31.41% during the experimental period. The instantaneous thermal efficiency increased by an average of 1.32 times for unpainted receiver and 1.36 times for black painted receiver with the increase in mass flow rate. By tracking the parabolic collector according to sun’s position, there is an average increase in instantaneous thermal efficiency by 1.1 times for unpainted receiver and 1.04 times for black painted receiver. The paper further reveals that the use of multiple helical tubes as a receiver for parabolic trough collector increases the overall efficiency of the collector in a substantial manner.

Water and CSP—Linking CSP Water Demand Models and National Hydrology Data to Sustainably Manage CSP Development and Water Resources in Arid Regions

A systematic approach to evaluate Concentrating Solar Power (CSP) plant fleet deployment and sustainable water resource use in arid regions is presented. An overview is given of previous work carried out. Once CSP development scenarios, suitable areas for development, and the water demand from CSP operations were evaluated, appropriate spatiotemporal CSP performance models were developed. The resulting consumptive patterns and the impact of variable resource availability on CSP plant operation are analysed. This evaluation considered the whole of South Africa, with focus on the areas identified as suitable for CSP, in order to study the impact on local water resources. It was found that the hydrological limitations imposed by variable water resources on CSP development are severe. The national annual theoretical net generation potential of wet-cooled Parabolic Trough decreased from 11,277 to 120 TWh, and that of wet-cooled Central Receiver decreased from 12,003 to 170 TWh. Dry cooled versions also experience severe limitations, but to a lesser extent—the national annual theoretical net generation potential of Parabolic Trough decreased from 11,038 to 512 TWh, and that of Central Receiver decreased from 11,824 to 566 TWh. Accordingly, policy guidelines are suggested for sustainable CSP development and water resource management within the context of current South African water use regulation.

Novel hybridization of solar central receiver system with combined cycle power plant

This paper presents a novel hybridization of a solar central receiver system via an open volumetric air receiver with a combined cycle. The exhaust gases from a gas turbine before entering a heat recovery steam generator are heated up by the solar heat in a volumetric receiver working as a supplementary firing, in contrast to the solarized gas turbine where the solar heat is introduced into an open or closed Brayton cycle. This hybridization does not require significant modifications in the gas power block. In this study the thermodynamic and economic issues are investigated and complemented with an optimization to demonstrate its technical feasibility. The obtained results reveal noticeable enhancements in solar energy conversion and power plant performance, where the net solar energy ratio may reach up to 23.5% and the overall efficiency about 64.4%. Assessment of the levelized cost of energy led to an estimated value of 0.0335 $/kWh which could be further reduced through an optimization which when the environmental issue is considered becomes more competitive. Furthermore, there is an important fuel saving of 7.07 Million $ and less pollutant emission about 0.33 Million ton over 30 years of operating service.

Parabolic Trough Collector and Central Receiver Coupled with Fresnel Lens: Experimental Tests

Renewable energies have a high impact on power energy production and reduction of environmental pollution worldwide, so high efforts have been made to improve renewable technologies and research about them. This paper presents the thermal performance results obtained by simulation and experimental tests of a parabolic trough collector with central receiver coupled to Fresnel lens, under different configurations on the pipe. The simulation method was computational fluid dynamics (CFD) analysis in SolidWorks ® software tool, which works with Naiver-Stokes equations to converge on a solution. Experimental tests were formed with all configurations proposed and three observations for each one, a total of 12 observations were performed in all research. As a result, the best thermal performance in simulation was achieved with the Fresnel lens and black pipe collector, with a maximum temperature of 116 °C under 1 000 W/m2 radiation, the same system achieved in experimental tests a maximum temperature of 96 °C with a radiation of 983 W/m2.

Modeling and parametric study of molten salt receiver of concentrating solar power tower plant

Central receiver is a key part of concentrating solar power tower plants, as it is not only responsible for the highly effective absorption of incident energy from the heliostat field, but also for efficient energy conversion from light to heat. Its performance will directly affect the system efficiency and generating capacity of the whole plant. In this paper, a comprehensive model of molten salt receiver, which uses the mult-section lumped parameter method, is clearly developed based on a molten salt solar power tower plant. In order to improve the reliability as well as the prediction accuracy of the developed model, the dynamic characteristics of the molten salt receiver are fully investigated by a step disturbance of external parameters. Besides, in order to improve the design level of molten salt receiver, the influence of key parameters on the performance of receiver system is also extensively studied. The results show that the incident solar flux, wind speed and absorptivity of heat-absorbing tube can greatly affect the performance of molten salt receiver system. In order to verify the validity of proposed model, the simulation results are compared with the published experimental data, and the results show the model has a high accuracy. Conclusions of this paper are good references for the design, control and commissioning of molten salt receiver systems.

Concentrating Solar Power (CSP)—Thermal Energy Storage (TES) Advanced Concept Development and Demonstrations

This paper highlights recent developments in utility scale concentrating solar power (CSP) central receiver, heat transfer fluid, and thermal energy storage (TES) research. The purpose of this review is to highlight alternative designs and system architectures, emphasizing approaches which differentiate themselves from conventional solutions. The push for increased efficiency and compatibility with high-temperature power cycles has driven the development of advanced receiver concepts utilizing various heat collecting media. Published work can be grouped into three technologies like US Department of Energy Gen3 CSP pathways: liquid, gas, and solid receivers, each with TES approaches ideally suited for system integration. Most experimental work has focused on material property investigation, with few system-level validations at meaningful scales. Innovative solutions utilizing advances in design, materials, and manufacturing are being pursued to realize advanced CSP-TES systems. Of those concepts built and tested, demonstrations have shown promise and remain topics of active development. With continued development, these systems can offer alternative pathways towards low-cost, dispatchable electricity production.

Performance characteristics of the Spiky Central Receiver Air Pre-heater (SCRAP)

Combined cycle concentrating solar power (CSP) plants provide significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to overcome barriers experienced to date.The SCRAP receiver is a novel metallic receiver technology aimed at pre-heating an air stream to about 800 °C, either prior to a combustion chamber or alternatively prior to a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures.A ray-tracing analysis demonstrated that the flux imposed on the absorber assemblies is dependent on the heliostat size. A thermodynamic computer model was developed to investigate the performance characteristics of the absorber assemblies (spikes) of the SCRAP receiver. The model was validated against an experimental test setup. Satisfactory agreement at various air flow rates was obtained.The thermal efficiency of the spikes was investigated and used to approximate the receiver’s solar-thermal efficiency. The receiver is predicted to perform at solar-thermal efficiencies exceeding 80%. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4–5%. A relatively large vulnerability to convective heat losses was identified. The pressure loss was found to be relatively low, compared to existing alternative receiver designs, with system pressure losses below 40 mbar achievable.

A fast and accurate methodology for the calculation of the shading and blocking efficiency in central receiver systems

In order to determine the efficiency factors of central receiver systems (CRS) in a reasonable time frame, in particular those relating to shading and blocking, the performance simulation and optimisation codes typically use simplification techniques. One frequent simplification is the assumption that the sunshape model is a point source sun.This paper examines the effect of the sunshape model on the shading efficiency, the findings illustrating a dependent relationship between the two. In particular, if the sunshape model considers the finite size of the solar disk, the performance results depend on the angle that the candidate heliostat forms with the main direction.Additionally, with the objective of reducing both computation times and error levels, a new method for the determination of the shading and blocking efficiency is presented, developed specifically for use in performance simulation and optimisation applications in CRS. The proposed method is compared with other methods, using the results of a conventional Monte-Carlo ray-tracing method as reference, through a study of computation times and error levels. The results demonstrate that the proposed methodology produces a reduction in both computation times and error values. The causes of the main errors associated with each method are also discussed.

Experimental study on the influence of input solar flux, air flow rate, and absorber parameters on honeycomb ceramic air receiver performance

Honeycomb ceramic absorbers are considered to be one of the most practical options for the air receiver of a solar central receiver plant. To explore the influence of the average input solar heat flux, air flow rate, and absorber geometric parameters on the honeycomb ceramic air receiver performance, six samples were tested under different conditions and the outlet air temperature, thermal efficiency, and anti-interference characteristics of the receivers were determined. The investigation showed that as the input solar flux or air flow rate increased, the change in the outlet air temperature and thermal efficiency had opposite trends. The sample with the shortest length, thinnest wall, and highest porosity had the best performance. Among the three absorber geometry parameters, the porosity was the dominant factor affecting the receiver outlet temperature and thermal efficiency.

Minimizing the Cosine Loss in a Solar Tower Power Plant by a Change in the Heliostat Position and Number

Concentrating Solar Power (CSP) focuses sunlight in order to use the heat energy of the sun. In a central receiver system configuration, many mirrors (heliostats) individually track the sun and reflect the concentrated solar energy onto a receiver on top of a tower. The receiver contains the working fluid which is heated by the concentrated solar radiation. The useful energy that absorbed by the water flows through the receiver in solar tower plant depending on the angle between the solar rays and the position of heliostat in the region of work. Heliostat will reflect the incident solar radiation in the direction of the receiver founded in the top of the tower, in order to get a maximum incident solar radiation on the heliostat reflection area. Because of the cosine factor loss effect due to the sun position is variable along the day from sunrise to sunset, which must be in a minimum value, therefore an automated tracking system with dual axes as a control system with sensors had been built and used to stay the sunrays incident on the receiver, and enable the heliostat to flow the sun where it was

Analysis and Assessment of Tower Solar Collector Driven Trigeneration System

Abstract This paper describes the development and performance assessment of a tower solar collector driven integrated system operating in trigeneration mode to generate electricity, heating, and cooling, in a carbon-free manner. The proposed system applies a heliostat-based central receiver unit as a base of solar energy input to drive the steam Rankine cycle which is combined with the process heater and the lithium bromide-water operated absorption chiller. An analysis is performed to monitor the behavior of energy and exergy efficiency at various operating conditions of the proposed trigeneration system. The computed results are authenticated with the reported literature. A comparison is made between the present findings and reported results in the form of exergy efficiency, total exergy destroyed, and energy efficiency. Consideration of process heat and cold along with electricity provides a promising increase in energy efficiency from 15.8% to 64.1% while the exergy efficiency is enhanced from 16.9% to 24.4%. Variation in direct normal irradiations from 600 W/m2 to 1000 W/m2 results in the significant rise of energetic and exergetic outcomes of the proposed trigeneration system. Out of 100% solar exergy supplied to the proposed trigeneration, 24% is generated as the exergetic output, 1.6% is lost to ambient, and the remaining 74.4% is the exergy destroyed in the system components.

Exploring ultra-high concentrator photovoltaic Cassegrain-Koehler-based designs up to 6000×.

Ultra-High Concentrator Photovoltaic (UHCPV) designs with up to more than 6000× geometrical concentration and optical efficiency of 80% are demonstrated in this paper by means of ray tracing simulations. These are developed based on Cassegrain-Koehler concentrators [Opt. Lett.41(9), 1985 (2016)], with four pairs of paraboloid-hyperboloid mirrors and a central receiver composed of four Cartesian ovals of revolution. Designs at different geometrical concentrations are analyzed based on their aspect ratios (F-number). The most compact designs exhibit highest optical efficiencies. Moreover, a 3015× geometrical concentration one-cell prototype, made of aluminum and PMMA (poly(methyl methacrylate)), is fabricated and characterized indoors, achieving an effective concentration of 938 suns. This represents the CPV module with the highest geometrical concentration that has been experimentally investigated that could be found in the scientific literature.

Thermal analysis of a spiral solar receiver for a small central receiver system: an experimental and numerical investigation

An analytical model is shown in the present study to evaluate the outlet temperature of the spiral receiver for nine numbers of the mirrors. An external receiver was designed, manufactured and experimentally evaluated by the concentrated central receiver system in order to study the change of heat transfer characteristics of fluid and temperature within the receiver. Steady state numerical simulation was carried out by using ANSYS Fluent to determine the outlet temperature of water. CFD results were validated by using the experimental results. The temperature of the fluid was varied with the number of heliostats and the mass flow rate. A maximum temperature of 92.4˚ C was obtained for nine heliostats with a mass flow rate of 0.0016 Kg/sec at the solar noon and average temperature of 84.4°C for the whole day. The heat transfer coefficient and pressure drop obtained from the spiral coil tube were 1.44 and 1.97 times higher than those obtained from the straight tube, respectively.

A new method for the selection of candidates for shading and blocking in central receiver systems

This paper presents a method for the selection of candidates for shading and blocking in central receiver systems (CRS). The main advantage of this algorithm is that it produces a reduced list of candidates with no upper limit on the total number, and it selects only those heliostats which produce real shading or blocking, eliminating redundant candidates. The objective is to contribute to a reduction in the execution times of the shading and blocking efficiency calculation in CRS, without a significant drop in accuracy.The method consists of three filtering levels, which progressively reduce the number of candidates, and it is specifically designed for use in performance simulation and optimisation applications for CRS. Its performance in this context has been compared with that of other selection algorithms, in terms of the number of selected candidates for each method and the execution times for determining the annual shading and blocking efficiency. The results indicate that the proposed method reduces the list of selected candidates to nearly 23% of those selected by other methods (spheres method) and up to 22% the execution times without affecting the numerical efficiency results.

Thermo-economic analysis of photovoltaic, central tower receiver and parabolic trough power plants for Herat city in Afghanistan

In Afghanistan, more than 60% of the population does not have access to a reliable source of electrical energy. A thermo-economic analysis is conducted to compare the performance of a Photovoltaic (PV), Central Tower Receiver (CTR) plant and a Parabolic Trough Collector (PTC) plant with and without storage for the city of Herat, in Afghanistan. The nominal capacity of both plants is 110 MWe. The PTC plant with energy storage has the highest efficiency of about 43% that is approximately 50% more than the PV plant, however, the PV plant has more uniform power production profile. The output power of PTC with energy storage is 25% more than output power of PTC without energy storage and output power of CTR plant is half of PTC plant with energy storage. The Levelized Cost of Electricity (LCOE) is 0.146 $/kWh for CTR plant, 0.063 $/kWh for PV plant, 0.1076 $/kWh for PTC plant with energy storage, 0.104 $/kWh for PTC plant without storage and 0.12 $/kWh for PTC plat without storage and without backup fossil fuel systems. Increase of incentive by 10% leads to decrease of LCOE by about 20% for PTC and 13% for PV and 12% for CTR power plants.

Recovering Structured Data From Superimposed Non-Linear Measurements

This work deals with the problem of distributed data acquisition under non-linear communication constraints. More specifically, we consider a model setup where $M$ distributed nodes take individual measurements of an unknown structured source vector $x_0 \in \mathbb{R}^n$, communicating their readings simultaneously to a central receiver. Since this procedure involves collisions and is usually imperfect, the receiver measures a superposition of non-linearly distorted signals. In a first step, we will show that an $s$-sparse vector $x_0$ can be successfully recovered from $O(s \cdot\log(2n/s))$ of such superimposed measurements, using a traditional Lasso estimator that does not rely on any knowledge about the non-linear corruptions. This direct method however fails to work for several "uncalibrated" system configurations. These blind reconstruction tasks can be easily handled with the $\ell^{1,2}$-Group-Lasso, but coming along with an increased sampling rate of $O(s\cdot \max\{M, \log(2n/s) \})$ observations - in fact, the purpose of this lifting strategy is to extend a certain class of bilinear inverse problems to non-linear acquisition. Our two algorithmic approaches are a special instance of a more abstract framework which includes sub-Gaussian measurement designs as well as general (convex) structural constraints. These results are of independent interest for various recovery and learning tasks, as they apply to arbitrary non-linear observation models. Finally, to illustrate the practical scope of our theoretical findings, an application to wireless sensor networks is discussed, which actually serves as the prototypical example of our methodology.

Heliostat field aiming strategies for solar central receivers

This thesis deals with the development of optical models for solar power tower technology. Specifically, this work is focused on modeling flux mapping and aiming strategies for central receiver systems (CRS). The resulting codes are applicable to CRS design and operation. This dissertation essentially presents four computational models. The first model, on which the rest of the models are built up, computes the flux density distribution incident on any kind of central receiver which is caused by a single heliostat. The procedure relies on the oblique projection of the receiver mesh onto the image plane, where an accurate analytic function, e.g. UNIZAR, is evaluated. Oblique projection is accomplished by transformation of coordinate systems. The 4-step projection method remarkably reproduces the distorted spot found for large incidence angles on the heliostat and the receiver. This basic model was validated against flux measurements on a flat receiver and Monte Carlo Ray Tracing simulations on a cylindrical receiver. Compared to SolTrace, the model takes 50 times less computation time and higher level of resolution. The second model was developed to determine canting errors in the facets of real heliostats. Based on a deterministic optimization algorithm, a procedure was set up to minimize the difference between computed flux maps and captured images on a lambertian target. Experimental images from THEMIS plant were employed to find out canting errors in selected CETHEL heliostats. From results of the model, one of the heliostats was successfully readjusted, significantly improving its optical quality, and validating the proposed methodology. The third model extends the basic model to superpose single heliostat flux maps in a whole field of heliostats. Shading and blocking losses are computed by parallel projection of neighbor heliostats. An aiming strategy, symmetric about the receiver equator, was developed on the basis of only one parameter: k, aiming factor. Nearly single equatorial aiming is achieved with k>3, while k=0 results in pointing to either upper or lower receiver edges. For the Gemasolar case study, an aiming factor equal to 2 yielded the most uniform flux maps, i.e. flat profile in the central region, and negligible increase in spillage losses compared to equatorial aiming. An optimal aiming strategy for molten salt receivers was implemented in the fourth model. An algorithm was developed to maximize receiver thermal output, while meeting at the same time corrosion and thermal stress limits; which were translated into allowable flux densities, AFD. Compared to unreliable single aiming, the optimized aiming strategy ensures receiver integrity and spillage losses only increase up to 4 percentage points. It was found that optimal aim points are, on average, slightly shifted towards the panel entrance. Despite the conflicting demand between adjacent panels in multi-panel receivers with serpentine flow pattern, the fit algorithm performs noticeable matching to the AFD profile. The resulting code takes around 2 minutes in a standard PC to compute the optimal aim points for a field made up of 2650 heliostats.

Performance Evaluation of Multiple Helical Tubes as a Receiver for Solar Parabolic Trough Collector

Solar parabolic trough collector consists of a parabolic reflector with a central receiver at a focal point through which heat transfer fluid is passed. Parabolic trough collector is used mostly in solar thermal power plants for generating electricity. This paper describes the experimental results of two straight tubes wrapped over each other to form a helically shaped receiver. The receiver was tested with aluminium material with and without black paint over it. Also, the helical tube receiver was tested with a glass cover over it, at two different mass flow rates and, with and without manual tracking. The tested instantaneous thermal efficiency ranges from 31.26% to 45.28% and the overall thermal efficiency ranges from 14.9% to 31.41% during the experimental period. The instantaneous thermal efficiency increased by an average of 1.32 times for unpainted receiver and 1.36 times for black painted receiver with the increase in mass flow rate. By tracking the parabolic collector according to sun’s position, there is an average increase in instantaneous thermal efficiency by 1.1 times for unpainted receiver and 1.04 times for black painted receiver. The paper further reveals that the use of multiple helical tubes as a receiver for parabolic trough collector increases the overall efficiency of the collector in a substantial manner.