Solar Central Receiver Research Articles

Analysis of Heat Transfer and Solar Radiation Absorption in an Irradiated Thin, Falling Molten Salt Film

A study was conducted to investigate the heat transfer characteristics of an irradiated, gravity-driven semitransparent fluid flowing over an opaque substrate. The physical model simulated is prototypical of cavity-type solar central receivers. Both absorption and emission in the fluid were considered, while scattering was neglected. The effects of model parameters such as substrate emissivity, fluid layer opacity, spectral nature of incident radiative flux, flow model, and fluid layer physical thickness were investigated. Results are presented for fluid mixed mean temperature and collector efficiency along the layer length in order to evaluate the performance of such systems.

Continuous duty solar coal gasification system using molten slag and direct-contact heat exchange

A new, very high temperature solar energy conversion technique which offers the potential of increasing the throughput and decreasing the cost of solar thermal coal gasification is described. Feedgas (CO 2 or steam) is heated to very high temperatures in a direct-contact droplet heat exchanger using slag droplets melted in a solar central receiver. The heated feedgas is then reacted with coal in conventional reaction vessels. Thermal storage at the full thermodynamic potential of the solar receiver is an integral feature of this approach and permits operation of the gasifier at full capacity during periods of no sun.

An assessment of solar hydrogen production using the mark 13 hybrid process

An assessment is presented of hydrogen production using a dedicated central solar receiver system concept coupled to a Mark 13-V2 hybrid thermochemical process. The system which is capable of producing about 10 6 GJ hydrogen per year was developed at the conceptual level. The total irradiance at normal incidence was taken as a parameter and varied from 1500 to 2500 kWh m −2 y −1 at a location with 30° latitude and 0.1 km altitude. The peak noon irradiance at normal incidence was taken as 0.95 kW m −2 and the mean total sunshine hours as 2333 h y −1. A flow sheet of the solar Mark 13-V2 hybrid process was developed to operate using the intermittent heat supply from the central receiver system and the continuous electric energy supply from outside. It was then evaluated using the models for the central receiver system, the solar receiver and the chemical process. It is found that for 2000 kWh m −2 y −1 total irradiance at normal incidence, the overall efficiency of the solar Mark 13-V2 process is about 21% and that the cost of the solar hydrogen is about $52 GJ −1.

Analysis and Design of the “Solar One” Thermal Storage Subsystem Heat Exchangers

This paper describes the analysis and design of the five kinds of heat exchangers used in the thermal storage subsystem of the 10 MWe Solar Central Receiver Pilot Plant, now becoming more known as “Solar One.” The paper discusses the practices and standards used in the designs of the heat exchangers, lists the heat exchanger design requirements, and discusses the process conditions. The design assumptions and constraints, the geometrical considerations, and the tradeoff studies that were conducted to optimize the designs are also discussed. A description of each heat exchanger reveals the final design solution. Novel and unique features of a power plant that must operate on a daily sun-cycle are identified.

Instantaneous Flux Distribution on a Solar Central Receiver

An important aspect in the design of a Solar Central Receiver system is the distribution of the solar flux on the receiver. In this paper, we present information for the Central Receiver Pilot Plant, Solar One, at Barstow, California, on the time variation of the receiver flux during cloud passage, at sunrise and during the day.

10-MWe Solar Thermal Central Receiver Pilot Plant

The Solar One Project is the world's largest solar electric generating station. This pilot-scale research and development experiment is a cooperative effort of government and private industry to demonstrate technical feasibility, economic potential, and environmental acceptability of the solar thermal central receiver concept. The project, which is formally known as the 10-MW Solar Thermal Central Receiver Pilot Plant, has been constructed in the Mojave Desert on 130 acres of Southern California Edison Company's Cool Water Generating Station near Barstow, California, and will supply 10 MW of electrical power to the Edison grid. Solar One is a joint project of the Department of Energy (DOE), Southern California Edison (SCE), the Los Angeles Department of Water and Power (LADWP), and the California Energy Commission. The solar portion of the facility was designed and constructed under the direction of the DOE, and the turbine-generator facilities, including the control building, were designed and constructed by SCE. This paper presents an overview of the project, discusses the costs and schedule, highlights the planned test program including operation and maintenance, and briefly discusses the experiences through October 1982.

A 1-MWe Central Receiver Type Solar Thermal Electric Power Pilot Plant

The design features, performance capabilities and operational experience to date of the solar thermal central receiver pilot plant at Nio-Cho, Japan, are discussed. Attention is given to the heliostat mirror structures and their alignment with respect to the receiver, the data acquisition system employed in performance tests, and the receiver efficiencies recorded at various times during daily operation. Also noted are heliostat tracking errors, and convective heat losses at the central receiver surface for a given air temperature and wind velocity.

Central Receiver System (CRS) in the Small Solar Power Systems Project (SSPS) of the International Energy Agency (IEA)

Attention is given to the design features and performance of the Small Solar Power Systems Project's Central Receiver System (CRS). The heliostat field used has a total reflective surface of 3655 sq m and focuses the irradiated power on an aperture plane of 9.2 sq m atop the tower. The cavity-type receiver is rated at 2840 kW at design conditions, of which 88.3 percent is absorbed by the liquid sodium heat transfer fluid as it is heated from 275 to 530 C. The major part of the CRS's Rankine power conversion cycle is a five-stage steam motor with two preheaters. Attention is given to CRS program funding responsibilities and development milestone chronology.

Evaluation of Air-Cooled Central Receivers

Air-cooled central receiver systems could potentially reach higher temperatures than other near-term solar receivers (molten nitrate salt, liquid metal, and water/steam receivers, for example); however, air has low density and poor heat transfer properties. Analyses were performed to determine whether air-cooled solar central receivers with metal absorber tubes could be competitive with other proposed central receivers. The air-cooled receiver designs analyzed in this study are based on a Boeing design. No air-based receivers with significantly greater potential than the metal tube design were identified in recent studies by Pacific Northwest Laboratory (PNL) and Sandia Livermore Laboratory (SNLL). In the design considered here, concentrated sunlight enters the cavity through apertures and strikes the walls, providing a diffuse source of radiation that heats the air in the metal absorber tubes. A small fraction of the incoming solar flux strikes the absorber surface directly. The receiver operates at approximately 3 atm, and has an outlet temperature of 815/sup 0/C (1500/sup 0/F). The molten nitrate salt receiver, in comparison, is a cavity design by Martin Marietta in which molten draw salt (50 percent NaNO/sub 3/ and 50 percent KNO/sub 3/) enters the absorber tubes at 290/sup 0/C (550/sup 0/F) and leaves at 566/sup 0/Cmore » (1050/sup 0/F). The incoming solar flux is absorbed directly by the tubes. Molten nitrate salt receivers have been shown to be attractive for electric power production and industrial process heat applications.« less

Solar Central Receiver Power Plants Status by Date of the First International Workshop at Claremont, USA, October 1982

Seven solar central receiver power plants are now either under construction or in operation in the world. The different technologies used for the construction of these plants, the instrumentation, the experimental programmes and the first results obtained from the plants in operation are discussed. This paper presents the status of the art by date of the first International Workshop on the Design, Construction and Operation of Solar Central Receiver Projects (19–22 October 1982, Claremont, USA). Conclusions and recommendations for the application of central receiver plants for electricity production and for solar fuels or chemicals production are summarized.

Solar-fossil HYBRID system analysis: Performance and economics

This study has developed a method of accounting for the dominant energy flows within a solar fossil hybrid power plant. The method is incorporated in a computer code called HYBRID, which can be linked to a solar central receiver code such as STEAEC. STEAEC, or a similar code, must be used to calculate the power from the solar central receiver (solar power) on an hourly or quarter-hourly basis. HYBRID determines the quantity of solar power directed to thermal storage, the quantity of solar power directed to a specified load, the amount of power retrieved from thermal storage, and the mass of fuel used by the fossil portion of the hybrid power plant. HYBRID uses the calculated fuel requirements to determine the present value of required revenue for the life of the plant. Fuel consumption is shown to be a dominant variable cost in the economic evaluation of a solar-fossil hybrid system. Fuel costs and other economic parameters are normalized to the present value of the capital investment. The range of normalized parameters is established to reflect economic unknowns and system design variability. It is shown that, under the most favorable economic conditions allowed in this study, the present value of the capital investment for a solar-fossil hybrid system should not exceed 2.5 time the present value of the capital investment for a comparable fossil power system if the hybrid is to be economically competitive. Under more probable conditions, this ratio declines to 1.5–2.0.

Solar Thermal Power Towers

The solar thermal central receiver technology, known as solar power towers, is rapidly evolving to a state of near-term energy availability for electrical power generation and industrial process heat applications. The systems consist of field arrays of heliostat reflectors, a central receiver boiler, short term thermal storage devices, and either turbine-generators or heat exchangers. Fluid temperatures up to 550°C are currently achievable, and technology developments are underway to reach 1100°C. Six solar power towers are now under construction or in test operation in five countries around the world.

An LQ-solution to a control problem associated with a solar thermal central receiver

The linearized process dynamics of the steam boiler in a solar-powered central receiver change abruptly when clouds interfere with the sun's rays. The steam temperature regulator used to maintain proper exit steam conditions must control a system with variable structure and discontinuous state trajectories. This paper investigates the quadratic-optimal control of such a system, and gives the design equations for the optimal regulator.

Crack tip oxidation of a superalloy in molten nitrate salt

Alloy 800 has been proposed for use in the receiver tube panel arrays of advanced solar central receiver (SCR) designs. In this application the alloy will be exposed to a molten mixture of sodium and potassium nitrate salts at temperatures ranging up to approximately 600/sup 0/C While these salts are routinely used in a variety of applications including metal heat treating and process heat transfer, common industrial experience has been limited to maximum temperatures of 400/sup 0/C - 450/sup 0/C. There is, therefore, considerable interest in the compatibility of these salts with containment alloys at the higher temperatures associated with SCR designs. Additionally, the containment alloy may be subject to thermally induced fatigue damage resulting from intermittent cloud cover and diurnal cycling. Previous work has found that slower near-threshold fatigue crack growth rates (FCGR) in Alloy 800 result when it is tested in molten nitrate salt at 600/sup 0/C (relative to air). This reduction in FCGR was attributed to an environmentally induced increase in oxidation resulting in oxide-induced crack closure. The purpose of the present work was to examine the influence of a typical nitrate salt composition on crack tip oxidation in Alloy 800 in order to determine if inmore » fact the proposed corrosion phenomena could explain the fatigue crack growth characteristics of the alloy.« less

A Method of Evaluating and Sizing Solar Cogeneration Systems

An analytical method for rapid evaluation and sizing of solar cogeneration systems is presented. The method, which utilizes a simplified system model and site-specific data on insolation and energy loads, is described herein and an illustrative application is discussed. The application considered is the use of a solar thermal central receiver cogeneration plant to supply the electrical and thermal energy needs of a hypothetical military base at Caliente, Nevada. The method has applicability to plants using other types of collectors.

Protective coatings for alloys in contact with molten drawsalt (NaNO3-KNO3)

Molten drawsalt (NaNO 3-KNO3) is being considered as the energy transfer and storage medium for many solar central receiver applications. In an effort to reduce the cost of the containment material while maintaining corrosion resistance, alloys with aluminide coatings have been examined while in contact with molten drawsalt for more than 6000 hours at 600 °C. The alloys examined were 2.25 Cr-1 Mo, 5 Cr-0.5 Mo, and 9 Cr-1 Mo low-alloy steels, and 316 stainless steel. The results show a steady, albeit slow, net weight loss over the course of the experiment. The weight loss has been attributed to spoiling of Al2O3 from the surface (the occurrence of Al 2O3 is a result of the aluminizing process) and dissolution of corrosion products NaAlO2 and/or NaFeO2 during post-immersion handling. Scanning electron micrographs of exposed surfaces revealed little or no corrosion of the base metal. It has been concluded that aluminide coated alloys could provide significant cost savings (~50 pct) relative to INCOLOY Alloy 800, and provide at least equivalent corrosion resistance.

Conceptual Design of an Advanced Water/Steam Receiver for a Solar Thermal Central Power System

This paper describes the conceptual design of an advanced water/steam receiver for a commercial-scale solar central receiver thermal power system. The objective was to develop a receiver concept featuring an optimum combination of cost, performance, and reliability. While interfaces with other major subsystems of the complete power plant were recognized, emphasis was on the design and and performance of the receiver. The baseline thermal rating of this receiver was 550 MW, and the steam outlet conditions were 12,860 kPa and 516 C. After technical and econmic evaluations, a quad-cavity, natural-circulation concept was selected as the preferred receiver design. It consists of four separate cavities in a single receiver unit, each cavity receiving concentrated solar energy from one quadrant of a surrounding heliostat field.

Geometric configuration factors for polygonal zones using Nusselt's unit sphere

The Energy Laboratory of the University of Houston has developed a computer simulation program called CREAM (Cavity Radiation Exchange Analysis Model) for application to the solar central receiver system. CREAM contains a geometric configuration factor generator based on Nusselt's method. A formulation of Nusselt's method provides the basis for a FORTRAN subroutine NUSSELT. Numerical results from NUSSELT are compared to analytic values and values from Sparrow's method. Sparrow's method is based on a double contour integral and its reduction to a single integral which is a approximated by Gaussian methods. Nusselt's method is adequate for the intended engineering applications, but Sparrow's method is an order of magnitude more efficient in many situations.

The Development and Design of Steam/Water Central Solar Receivers for Commercial Application

Central tower solar receivers have many similarities to fossil-fuel-fired boilers in design, manufacturing, and construction. Babcock & Wilcox has designed several types of steam/water solar receivers. A typical DOE approach is to design, construct, and test in sequence a Subsystem Research Experiment (SRE) and a pilot plant, and then to scale it up to commercial sizes. In contrast, the normal approach of boiler manufacturers, and specifically Babcock & Wilcox, has been to design a sectionalized receiver and modularized components so they can be assembled in various sizes, capacities, and geometries to meet the requirements of the system and characteristics of the collector field. A receiver design having such features and using commercial-size and shop-assembled modules is described. Special design features are described to overcome the unbalance of north-to-south field flux ratios, effect of partial and transient cloud patterns, and a large number of thermal cycles. A parametric study to determine the maximum allowable heat flux on the heat transfer surface components is also described.

Solar Technology Applications to Enhanced Oil Recovery

Abstract One possible near-term application for solar thermal technologies is the production of steam which could be pumped underground te increase the amount of petroleum which could be recovered from an oil field. This article compares two types of solar thermal technologies—solar troughs and central receivers—with conventional means of enhanced oil recovery (EOR) to determine, first, if solar technologies offer a viable EOR option and, second, how they compare with other steam-drive EOR alternatives. It analyzes these options from the technical, economic, institutional, and environmental perspectives. The paper concludes that solar EOR is, at present, not an economically attractive alternative, largely due to existing technical uncertaintities; possible environmental benefits do not appear to be a driving consideration; finally, tax incentives rather than government demonstration programs would seem to be the most effective means of encouraging solar EOR technology.