Central Receiver Research Articles

Material selection for solar central receiver tubes

The severe operation conditions and great capital investment of solar power tower central receivers motivate the lifetime analysis of a molten-salt external-cylindrical-tubular receiver, considering five alloy alternatives for its tubes manufacturing: Haynes 230, alloy 316H, Inconel 625, 740H and 800H. An analytical low-computational cost methodology is employed, considering the temperature dependence of tube material properties, elastic-plastic stresses/strains and stress relaxation. Thus, creep and fatigue experimental data available in the literature for these alloys are compiled in this work, providing the coefficients required for the methodology followed. A great alloys operation limitation is the film temperature to avoid corrosion issues; the most permissive are H230, 740H and 800H (650 °C), followed by Inconel 625 (630 °C) and 316H (600 °C). This, and the twice the yield strength, is regarded to set the heliostat field aiming strategy as equatorial as possible for each alloy, resulting in great power production divergences: 24% and 65% less for 625 and alloy 316H receivers with respect to the 740H receiver. Then, the lifetime analysis for a clear design day operation, representative of the receiver during ideal operation, is performed. The stress relaxation regard becomes critical for the accurate damage prediction; alloys 316H and 800H show stress reset during operation, not benefitting from a global stress relaxation. Thus, 800H exhibits a poor endurance. For the clear-day assumption, 740H shows the best lifetime and costs/power performance; the levelized cost of alloy of H230, 625 and alloy 316H is 0.01, 0.09 and over 0.25, respectively, with respect to 740H. • Integral analysis of molten salts solar central receivers in different alloys. • The coefficients to characterize creep and fatigue in these alloys are obtained. • Maximum film temperature allowable of each alloy sets a remarkable operation limit. • The stress relaxation without stress reset greatly extends the receiver lifetime. • Levelized cost of alloy metric for comparison by means of costs and energy produced.

High-temperature latent thermal storage system for solar power: Materials, concepts, and challenges

Limited reserves of fossil fuels, increased world energy demand and swelling of environment pollution drive a transition towards renewable energy resources which can deliver 3E objectives (Economic, environmental and energy security). However, the inherent intermittency necessitates efficient energy storage systems to harness the true potential of renewable resources. In this context, high-temperature latent heat storage (LHS) using phase change medium (PCM) can be a promising alternative to address the challenges of the variable renewable energy generation with respect to time and space. Currently, central receiver-based 3rd Gen concentrated solar thermal (CST) plant operating at high-temperatures (800-1000 °C) is the most attractive technology to convert solar energy to heat. Moreover, advanced power-generating cycles such as supercritical CO2 (sCO2) Brayton cycle operating at high-temperature can reduce the Levelized cost of Energy (LCoE) by achieving higher cycle efficiency. Hence, coupling a high-temperature LHS between the central receiver system and sCO2 cycle can have dual benefits: increase in dispatchability of energy and reduction in LCoE. Furthermore, high-temperature LHS can be devised to store high-grade energy such as spillage of energy from Photovoltaic (PV), wind power plant, and waste heat from energy-intensive industries (e.g. glass melting furnace). This article reports a holistic approach to review different components and design aspects of high-temperature LHS with techno-economic challenges to be overcome. A preliminary numerical study has been performed to predict the melting behavior of high-temperature silicon using COMSOL Multiphysics. Based on the review, two configurations of high-temperature LHS have been illustrated to produce continuous and cost-effective electricity. The first layout is high-temperature LHS coupled with 3rd generation (Gen) CST and the second one is a standalone high-temperature LHS device with Thermionic-photovoltaic (TIPV) diode.

Dynamic simulation and performance evaluation of a novel solar heliostat-based alkali metal thermoelectric converter system

Solar tower plants (STPs) can foster reduce toxic emissions and a cleaner environment. Here, to step forward in this advance, this system is employed as a heat source for an alkali metal thermoelectric converter (AMTEC). Thermal energy storage (TES) is applied to stabilize the performance of the hybrid system along with solar irradiation fluctuations. The considered system is investigated on three different days for the humid subtropical climate of Bandar Abbas, Iran. This study's primary outcome and contribution is a novel simulation framework via TRNSYS to predict the performance of the system under fluctuations of solar irradiation at this site. Both TES and STP systems are defined in TRNSYS software as a new component type via utilizing the Fortran program. The effects of various parameters, including the total energy absorbed by the central receiver, the thermal capacity of TES, and the heliostats field area, are investigated on crucial output parameters of the AMTEC. The mass flow rate of the heat transfer fluid at several areas is then studied in different operating conditions. The optimum area for the heliostats (14,500 m2), leading to the highest AMTEC efficiency (18%) is determined, which requests a TES tank volume of 28.13 m3. This system is noticed to have its most remarkable performance in June and July.

A detailed account of calculation of shading and blocking factor of a heliostat field

The shading and blocking factor plays a significant role in the design of a heliostat field. It is the most computationally expensive task during the optimization process of a heliostat field. Over time, different methods have been developed to calculate the extent of the optical losses associated with shading and blocking. This paper focuses on the famous center point projection method and its implementation using Matlab. This work provides detailed procedures from the perspective of programming and simulation of central receiver systems. The underlying assumptions, the algorithm's strengths, and weaknesses are highlighted. The procedure and simulation parameters will help in developing optimization algorithms for designing high-efficiency heliostat fields. A dense radial staggered heliostat field is used for testing the performance of the algorithm. The field efficiency is calculated at different design points. The results show that the shading loss of the field changes with time, whereas there is negligible variation in the blocking loss. The instantaneous shading loss of a dense radial staggered field on December 21, noontime is 2.12%, whereas the blocking loss is 1.52%.

High-Performance SiC–Based Solar Receivers for CSP: Component Manufacturing and Joining

Concentrated solar power (CSP) is an important option as a competitive, secure, and sustainable energy system. At the moment, cost-effective solutions are required for a wider-scale deployment of the CSP technology: in particular, the industrial exploitation of CSP has been so far hindered by limitations in the materials used for the central receiver—a key component in the system. In this context, the H2020 NEXTOWER project is focused on next-generation CSP technologies, particularly on advanced materials for high temperatures (e.g., >900 °C) and extreme applications environments (e.g., corrosive). The research activity described in this paper is focused on two industrial solutions for new SiC ceramic receivers for high thermal gradient continued operations: porous SiC and silicon-infiltrated silicon carbide ceramics (SiSiC). The new receivers should be mechanically tough and highly thermally conductive. This paper presents the activity related to the manufacturing of these components, their joining, and characterization.

Dynamic aiming strategy for central receiver systems

Aiming strategies in central receiver systems search for an optimal assignment between heliostats and aim point on the receiver surface. In this work, we develop an accelerated aiming strategy which can be used for dynamic scenarios such as short-term environmental influences. The strategy bases on the linear formulation of the problem. To achieve a performance close to real-time, we present several accelerations based on carefully chosen methods to reduce the problem size. The performance of different solvers is evaluated and the problem reduction is adjusted according to accuracy, prediction time and computational run-time. The accelerated aiming strategy is applied to central receiver systems with up to 8600 heliostats in a dynamic test scenario with cloud shadows passing over the heliostat field. The accelerated aiming strategy is effective enough to be used as a real-time control strategy.

Optimizing Vehicle Fleet and Assignment for Concentrating Solar Power Plant Heliostat Washing

Concentrating solar power central-receiver plants use thousands of sun-tracking mirrors, i.e., heliostats, to reflect sunlight to a central receiver, which collects and uses the heat to generate electricity. Over time, soiling reduces the reflectivity of the heliostats and, therefore, the efficiency of the system. Current industry practice sends vehicles to wash heliostats in an ad hoc fashion. We present a mixed-integer nonlinear program that determines wash vehicle fleet size, mix, and assignment of wash crews to heliostats to minimize the sum of (i) the revenues lost due to heliostat soiling, (ii) the costs of hiring wash crews and operating the vehicles, and (iii) the costs of purchasing wash vehicles. We establish conditions for convexity of the objective function, and then propose a decomposition method that enables near-optimal solutions to the wash vehicle fleet sizing and assignment problem on the order of a couple of minutes. These solutions yield hundreds of thousands of dollars in savings per year over current industry practices.

Theoretical and experimental investigation of a novel point‐focus Fresnel collector system with a novel receiver

Here, experimental results for testing a novel solar concentrating system are presented. The novel receiver is tested on a technology that combines the two proven concepts of solar concentrating technologies (linear Fresnel reflector (LFR) and central receiver technologies) into a new concept called focal point Fresnel collector (PFFC) with a polar sun-tracking system. The PFFC system works by concentrating direct solar irradiation using several flat mirrors positioned over a square-rotating surface that follows the sun. Considering the solar elevation, the reflection is achieved using the Fresnel reflection concept. Rectangular mirrors of LFR technology are discretised into small square mirrors to achieve point focusing. A concentration ratio of 600 has been achieved, which is like that of parabolic dish (PD) systems. Mathematical modelling of the system is presented along with the experimental results. Furthermore, the PFFC system with the novel receiver provides similar thermal efficiency with comparatively higher manufacturing ease than the PD system. Besides, a maximum thermal efficiency of 87% has been achieved.

Thermal stress and fatigue damage of central receiver tubes during their preheating

• Transient temperature and thermal stress in tubes of CSP receivers are modelled. • The Vant-Hull algorithm is used to define the incident heat flux during tube preheat. • Large temperature gradients and a stress peak occur in the first 120 s of preheat. • The standard Vant-Hull algorithm may be unable to preheat tubes in windy conditions. • Fatigue damage due to preheat is less than 5%, avoiding creep-fatigue interaction. Preheating of the absorber tubes of a central receiver is a crucial operation in the start-up of current solar power tower plants (SPT) working with molten salt as a heat transfer fluid. In the preheating, a subset of the heliostat field is aimed at the receiver to produce an incident heat flux capable of heating the tube walls before they are filled with the molten salt. Incident radiation should be kept above a minimum as an insufficient level of preheating may lead to the freezing of the incoming flow of molten salt, interrupting the receiver operation. However, too much incident heat flux in the preheating causes severe thermal gradients in the walls of the tubes, leading to extremely high thermal-stresses and the eventual fatigue damage of the receiver. The present work numerically characterizes the temporal evolution of the temperature and thermal-stresses in the absorber tubes made of Haynes 230 alloy. This is done for two examples of SPT plants, i.e. Gemasolar and Dunhuang, with the aim of detecting when and where the largest temperature gradients and mechanical stresses appear during the tube preheating and evaluate their impact on the fatigue damage of the receiver tubes. The results show that during the first seconds of preheating, the front side to the tube is rapidly heated but the temperature at rear side of the tube is barely modified, causing a great non-uniformity of temperatures. This effect is enhanced when the tube diameter is increased because the heat requires more time to reach the rear side of the tubes. The peak values of the temperature gradient and the von Mises stress are reached during the first minutes of the preheating. Besides, under windy conditions, the preheating procedure proposed by Vant-Hull may be insufficient to preheat the receiver. Furthermore, in all the cases analyzed, the estimated fatigue damage of the tube is much less than the 5 % upper limit to avoid significant creep-fatigue interaction. This indicates the Vant-Hull algorithm does not compromise the structural integrity of the studied receiver tubes.

Thermal Analysis of a Parabolic Trough Collectors with Cylindrical and Fractal Receiver Under Serial-Parallel Configuration

Solar collectors are one of the higher technologies that involve solar radiation available on surface Earth. However, actually, numerous researches have been developed to improve thermal performance in all system, including surface concentration, receiver, transfer fluid and glass cover. The results of the design, the modeling, and the simulation of a parabolic trough collector and central receiver with three different geometries coupled under serial and parallel configuration are presented in this paper. Different geometries have been proposed in receiver pipe in order to increase transfer surface area and improve thermal efficiency. Each model has been simulated by Computational Fluid Dynamics (CFD) in SolidWorks® software specialized on thermal analysis. As results, the maximum temperature of 86°C has been achieved in this research with two collectors with fractal F1 receiver coupled in parallel configuration. In addition, the lower temperature has been obtained with a single cylindrical collector with a final temperature of 61°C. The principal contribution of this works is the analysis of the best configuration to a solar concentrate system as parabolic trough collector, under a serial or parabolic scheme with the purpose of enhancing the heat transfer on receiver and working fluid. Likewise, a novel design in receiver is proposed based on fractal geometries, which show in the study the best temperature results.

Methods for the treatment of a flue gas stream using catalytically-enhanced sorbent compositions

Solar thermal concentrated power is an emerging technology that provides clean electricity for the growing energy market. To the solar thermal concentrated power plant systems belong the parabolic trough, the Fresnel collector, the solar dish, and the central receiver system.For high-concentration solar collector systems, optical and thermal analysis is essential. There exist a number of measurement techniques and systems for the optical and thermal characterization of the efficiency of solar thermal concentrated systems.For each system, structure, components, and specific characteristics types are described. The chapter presents additionally an outline for the calculation of system performance and operation and maintenance topics. One main focus is set to the models of components and their construction details as well as different types on the market. In the later part of this article, different criteria for the choice of technology are analyzed in detail.

Assessment of the time resolution used to estimate the central solar receiver lifetime

This study assesses the impact of the time resolution and design day on the estimated lifetime of the molten-salt external tubular receiver of a solar power tower, one of the most damaged components of these facilities, considering operation under clear conditions. A global analysis is performed by first determining the heliostat field aiming strategy; the receiver operation limits are set to keep a low enough film temperature and to avoid the stress reset. The former prevents excessive corrosion rates of the tubes while the latter assures the global stress relaxation, which significantly reduces their damage during the receiver cyclic operation. Time steps of 60, 30, 15, 5 and 1 min are tested considering the spring equinox design day, as well as only solar noon conditions. The latter significantly underpredicts the receiver lifetime with respect to the 1-min case, being early discarded. The lifetime in the most damaged panel is underestimated over 18% and 16% using the 60- and 30-minute time steps, dropping to 2.57% using the 5-min time step at a reasonable computational cost. Finer resolutions enable more precise aiming strategy selection, decreasing the receiver peak fluxes. Lastly, a set of 8 representative days for the year, equally spaced in solar height, is more accurate than using the spring equinox alone, which results in an underestimate of the receiver lifetime that may be overly conservative. The summer solstice is the least-damaging day, with the lifetime decreasing as approaching the winter one, as long as the storage tank is filled.

Dual-tower CSP plants: optical assessment and optimization with a novel cone-tracing model

Solar tower systems show significant prospects based on their room for improvement in the solar thermal industry. Despite not being an entirely new concept, multi-tower systems have not been extensively studied in the literature yet. An optical optimization model is presented to evaluate the feasibility of dual-tower systems, where each heliostat can select the most convenient receiver. There is a number of optimization variables, which makes it essential to implement a fast optical algorithm capable of evaluating the field optical efficiency. Taking advantage of the tower central receiver's axial symmetry, an integration method is proposed to work out the individual spillage for each heliostat. As a result, an optimal design has been accomplished where 32 representative days (with several time-points each) have been taken into account to assess the yearly-averaged optical efficiency of the whole solar field. Thus, it can be concluded that a ∽1.5% increase in the annual optical efficiency can be achieved with respect to the analogous single tower system.

Coalition-based interference mitigation method for wearable sensor transmitter–receiver antenna communications

Wearable sensor technology provides autonomous signal monitoring of patient data based on physical changes observed in their bodies. The observed vitals are transmitted to the medical center's receiver for processing and suggestions. The transmitting and receiving pair of antennas rely on shared channels to exchange signals to resolve the challenges in interference. This study proposes a coalition-based interference mitigation wireless antenna (CIM-WA) to improve the signal monitoring of patient data. CIM-WA relies on the cooperative agreement of the transmitter and receiver for distinguishing sharing intervals. In CIM-WA, synchronization between the devices is accounted to maximize degree of freedom (DoF). A smart decision-making process is included in the interference mitigation for verifying the synchronized behavior of the communication process. The proposed method's performance improves the common rate and DoF by 27.6% and 10.46%, respectively. Similarly, it reduces the relative error, signal-to-noise ratio, and processing time by 20.3%, 10.8%, and 14.36%, respectively.

Review on advance tubular receivers for central solar tower system

This review focused on central tubular receiver modelling to obtain concentrated solar energy. Required specifications involved with efficient low cost receiver with suitable material which able to absorb concentrated solar radiations. This type of advance receivers shows excellent performance in the commercial and domestic applications. Review shows compiles literature engaged in mechanical and thermal modelling of receiver. Also highlighted on various geometries, tube sizes and various heat transfer fluids and their effect on overall performance of receiver. Recently authors concentrated on CFD simulations of different kind of receiver and put forth advanced design which offers superior flexibility and accuracy also explains stresses generated in the tube of receiver. The selection of stress theory is impacting on the mechanical life of the receiver with different approaches presented. Extensive technical analysis is investigated on different receivers for internal and external tubular geometry. Effect of heat transfer for different geometry is also observed. In this paper different aspects discussed thoroughly like receiver design, Numerical simulation, outdoor and indoor testing facilities, thermal efficiency and desired outlet temperature, benefits, future challenges, and research needs.

High-Temperature Monitoring in Central Receiver Concentrating Solar Power Plants with Femtosecond-Laser Inscribed FBG.

This work deals with the application of femtosecond-laser-inscribed fiber Bragg gratings (FsFBGs) for monitoring the internal high-temperature surface distribution (HTSD) in solar receivers of concentrating solar power (CSP) plants. The fiber-optic sensor system is composed of 12 FsFBGs measuring points distributed on an area of 0.4 m2, which leads to obtain the temperature map at the receiver by means of two-dimensional interpolation. An analysis of the FsFBG performance in harsh environment was also conducted. It describes the influence of calibration functions in high-temperature measurements, determines a required 10 nm spectral interval for measuring temperatures in the range from 0 to 700 °C, and reveals wavelength peak tolerances in the FsFBG fabrication process. Results demonstrate the viability and reliability of this measuring technique, with temperature measurements up to 566 °C.

Experimental Study of Concentrated Solar Power on Heat Feed Water Heaters in Steam Power Plants in Iraq

For generating power, solar energy is counted a good exporter. Iraq is located in a hot zonewith latitude from 32 degree N to 36 degree N. In Iraq, the average solar radiation is about 7kilowatt hours / day.In this work, central receiving tower was used to obtain steam using the available solar energyin summer and winter. To heat the feed water heater of South Baghdad Electrical Steam PowerPlant, steam utilization for this purpose. In the project, manufacturing the central receivertower, which is consisting of 150 mirrors fixed upon 75 manual tracking heliostats arranged forutilization the solar radiation concentrated on the central receiving tank (CRT). Pipes systemswere used for hot water or steam exits from receiver. In this study, the central receiver tank(0.5m*1m) was filled with 157 liter of water. The experimental work was run for one yearfrom June 2015 – May 2016. The outlet temperature of water from central tower receiver wassteam for (July and August 2015) and hot water with high temperature for other months of theyear. The results obtained from our system, solar shares for heating the feed water heater ofSouth Baghdad Electrical Steam Power Plant up to 1.86 % and an annual average of 1.03%.Temperature, power concentration factor and system efficient are greatly influenced by thenumber of heliostats used. A sample of calculations is used to evaluate the mathematical dataof hot water and steam temperatures obtained from this study. These values are approximatewith experimental data when compared together.

Optimal Design of Solar Receivers in CSP Plants: Effects of Facility Location

This work presents a two-stage approach for the design and evaluation of the performance of solar central tubular receivers. First, the unit design is obtained using a mixed-integer nonlinear programing (MINLP) optimization problem, considering the radiation profile and the weather of the location. Later, with the design fixed, the NLP is solved to determine the performance of the receiver during a year. Three different locations are studied (Almería, Arizona, and Scotland), each of them with their characteristic radiation and weather. The designs obtained show the effect of the location on the size of the different elements of the receiver. The performance over a year presents the heat-transfer features as well as the effect of the wind speed profile affecting the convective heat transfer. The number of trade-offs results in the need for a comprehensive analysis for the design of these units toward reducing the pressure drop but considering the increase of the thermal stress on the tubes.

TRNSYS Modeling and Simulation of a Solar-Fuel Hybrid Thermal Power Plant based on a Central Receiver System

TRNSYS Modeling and Simulation of a Solar-Fuel Hybrid Thermal Power Plant based on a Central Receiver System

Dispatchable solar power using molten salt directly irradiated from above

Concentrating solar power (CSP) with thermal energy storage (TES) presents the major advantage over solar photovoltaics of dispatchability. High thermodynamic efficiencies achieved by collecting and storing heat at higher temperatures, and recent maturing of the technology, are making molten-salt central receiver plants the preferred option for CSP. To explore potential further improvements in CSP efficiency and cost the world’s first direct absorption molten salt volumetric receiver/storage system was built at pilot scale, commissioned and monitored. In this demonstration a 100 kWth beam-down tower directs solar radiation through a final concentrator into the open aperture of a 1.94 m high and 1.25 m internal diameter tank receiver situated near the ground. The receiver tank is filled with 3,800 kg of 60–40 wt% NaNO3-KNO3 and serves as a stratified or mixed single tank thermal store that can satisfy evening peak loads or provide baseload power through the night. Compared to the parasitic loads of a conventional tower-receiver plant, the energy needed for salt transport from receiver to TES and morning preheat is negligible for this new system. The hot-spot problem of tubular receivers is eliminated and. the combined receiver/storage tank reduces component costs. In-situ initial melting was accomplished using solar energy as the primary input. Thermal stratification was maintained by daily cycling of a divider plate and occasional mixing plate actions and hot spots were never observed during several months’ operation between 250 and 500 °C. Three cycles of complete salt freezing and in-situ on-sun re-melting were tested with no operational difficulty and no discernible damage.