Solar Energy Receiver Research Articles

Optimal Design and Operation of a Solar Energy Receiver and Storage

Optimization of design and operation is presented for a solar energy receiver combined with a thermal energy storage. The concentrated solar power on-demand (CSPonD) concept, which can be described, in brief, as a volumetric solar energy receiver system combined with a modified raft thermocline concept, is considered. The CSPonD concept is assumed to be providing heat for a general cogeneration scheme where power production is the main product of the cogeneration. With a constant power production, a secondary process is assumed to consume the process heat from the CSPonD and power cycle. Models are developed for thermal analysis of the energy storage, taking into account hourly and seasonal variations in the solar energy as well as the heliostat field efficiency. Nonlinear programming (NLP) is used for optimization of the design and operation. The sequential method of optimization and a heuristic approach (parallel computing) are implemented using an equation-oriented modeling environment and gradient-based local solvers. A strategy is presented to design and operate the plant, considering the significant seasonal variations in the solar energy. Three case studies are presented. The first one optimizes the design based on a design day and a desired thermal duty. The other two address optimal yearly operation of the plant. The results of the optimization case studies show that (a) the CSPonD concept aids in handling variations (hourly, daily, and seasonal) in solar energy, (b) CSPonD is a promising concept for cogeneration, (c) the mass of salt required in the CSPonD concept is not significantly lower than the salt required in a single-tank thermal energy storage system.

Solar energy conversion through seaweed photosynthesis and zero emissions power generation

The present paper is aimed at describing a “closed cycle” power plant scheme (Solar Oxygen Fuel Turbine (SOFT)) with macroalgae (seaweed) cultivation in a pond, combustion of its organic matter in a fluidized bed boiler using the Rankine cycle, and return of the combustion products to the pond to feed the algae. The oxygen used for combustion is released to the atmosphere during photosynthesis. It is further elaborated in a paper presented at ECOS2005 in Trondheim. As a renewable fuel, the seaweed Ulva lactuca is selected. Its growth rate in many experiments (in the literature) is 0.1–0.2 per day, the heating value of its dry weight is 19 MJ/kg, and its optimal concentration in salt water is 1:1000. The energy efficiency is less than in photovoltaics, but the energy expenditures to construct the pond as a solar energy receiver are much less, so it gives some economic benefits. For a power unit of 100 kW, the pond surface is about 4 hectare. The cultivation of seaweed in sea-water ponds is well developed in Italy and Israel for water cleaning and chemical production. Construction in the future of a SOFT system near the Dead Sea in the Israeli desert would provide the country with needed power, chemicals, and fresh water using solar energy. The system is protected by United States Patten no. 6 477 841 B1 dated 12.11.2002 with priority in Israel dated 22.03.1999. Many more benefits to the customer than are in the patent text are highlighted in the paper, including fresh water by desalination. In view of the active work in Italy on water cleaning using Ulva and contaminants in the water as nutrients for an increase of the biomass productivity, an additional target of the SOFT cycle might be incineration. Some suppositions of the use of a desert surface for massive scale use of ponds are given.

A solar-driven combined cycle power plant

The main results of a feasibility study of a combined cycle electricity generation plant, driven by highly concentrated solar energy and high-temperature central receiver technology, are presented. New developments in solar tower optics, high-performance air receivers and solar-to-gas turbine interface, were incorporated into a new solar power plant concept. The new design features 100% solar operation at design point, and hybrid (solar and fuel) operation for maximum dispatchability. Software tools were developed to simulate the new system configuration, evaluate its performance and cost, and optimize its design. System evaluation and optimization were carried out for two power levels. The results show that the new system design has cost and performance advantages over other solar thermal concepts, and can be competitive against conventional fuel power plants in certain markets even without government subsidies.

Thermochromic complex compounds in phase change materials: Possible application in an agricultural greenhouse

The possibility to combine two physico-chemical phenomena is studied in this work in order to attain simultaneous control of temperature and light intensity in a greenhouse: (a) isothermal heat storage in phase change materials and (b) thermochromic behavior of complex compounds dissolved in the phase change materials. Two binary mixtures melting near the ambient temperature were studied: (a) 0.925 Ca(NO 3) 2·4.06 H 20+0.075 CaCl 2·6.11 H 2O melting at 35.6°C and (b) 0.9 CH 3CONH 2+0.1 Ca(NO 3) 2·4 H 2O, melting at 27.7°C. The melting temperature, the enthalpy of fusion and the heat capacity of both mixtures were determined from DSC measurements. Both mixtures showed to be suitable solvents for the formation of consecutive cobalt(II) chloride complexes. The compositions of the complex compounds were adjusted in each mixture so that the absorption spectra in visible spectral range exhibited low absorbance at the melting temperature and a pronounced increase of the absorbance and/or change of color with the increase of temperature in the range relevant for passive solar energy receivers. The combined latent heat storage and the outstanding reversible change of the optical properties of the dissolved complex compounds with temperature is proposed to be applied in solar heated agricultural greenhouses in areas with fluctuating climate conditions. The increase of absorbance with temperature acts as an auto-regulated shading protection from overheating.

Natural convection heat transfer in horizontal annulus with an open trough (black body solar energy receiver)

An experimental study was carried out to investigate natural convection heat transfer inside a horizontal annulus with an open longitudinal trough that simulates a black body solar energy receiver. The effect of the trough location and annulus eccentricity on Nusselt number is presented. The results indicated that the Nusselt number lies between the two limiting cases of closed annulus and free horizontal cylinder. An enhancement of natural convection takes place by positioning the inner tube below the annulus center line (negative eccentricity). No significant changes in Nusselt number were found to occur when the trough was tilted between the vertical position and 45° from the horizontal.

Natural convection heat transfer in horizontal annulus with an open trough (Black Body Solar Energy Receiver)

An experimental study was carried-out to investigate natural convection heat transfer inside a horizontal annulus with an open longitudinal trough, that simulates a black body solar energy receiver. The effect of Rayleigh number, the annulus eccentricity, and the trough location on Nusselt number is presented. The results indicated that Nusselt number lies between the two limiting cases of closed annulus and and free horizontal cylinder. At low Rayleigh number, convection is relatively weak and Nusselt approaches the value of closed annulus. As Rayleigh increases, Nusselt number approaches the value of free cylinder. An enhancement of natural convection takes place by positioning the inner tube below the annulus center line (negative eccentricity). No significant changes in Nusselt number were found to take place when the trough was titled between the vertical position and 45 degree from the horizontal.

Platinum-Based High Temperature Selective Absorber Coatings

Magnetron sputtering technology enables large substrate areas to be coated, and is therefore applicable to the production of solar energy receivers. Co-deposited platinum-alumina graded cermet coatings have been investigated and their great thermal stability in air makes them highly suitable for medium temperature collectors.

Optimum Radius of Cylinderical Envelope of Solar Energy Receiver.(Dept.M)

Optimum Radius of Cylinderical Envelope of Solar Energy Receiver.(Dept.M)

Technical and economical evaluation of an MSF solar energy powered desalination plant

Technical and economical features of an MSF desalinatlon plant are investigated taking into consideration different solar energy receivers. The MSF desalting plant is designed as a 500 m 3/d, 46 stage, cross tube type with a top brine temperature of 121°C and a specific heat consumption of about 38.5 Kcal/kg of distillate. Different systems to trap solar energy have been considered, taking into account process parameters such as: 1. outlet temperature of fluids from solar receivers 2. performances 3. power production system 4. power consumptions 5. energy storage 6. back-up and energy integration systems 7. reliability of both desalting and solar equipment Plant lay-out proposed is described in the paper including process flow-sheet and energy balance, and it is discussed with reference to maximum savings regarding both costs and energy.

Health and safety hazards associated with solar concentration systems

This paper discusses the primary health and safety hazards associated with solar concentration systems. The limiting hazard is chorioretinal damage. This article also discusses the methodologies derived to compute the unique safety and health hazards associated with solar energy collector and receiver systems. Research in this area is continuing, especially for eye hazards, with more extensive work planned.

Heat Mirrored Solar Energy Receivers

RANSPARENT heat mirrors are thin films that transmit visible light but reflect infrared radiation. This paper investigates the potential utilization of this wavelength selective property in the process of trapping incident solar energy and its conversion to heat in a high-temperature (5401650°C) windowed cavity. The heat mirror film permits the solar energy to enter the cavity but reflects part or all of the internally generated blackbody (heat) radiation as it attempts to escape. The characteristics and durability of a number of transparent heat mirror films developed at the MIT Lincoln Laboratory for solar energy applications have been reported. l'3 These transparent heat mirror film types include metal films1 (e.g., Au and Ag), semiconductors2 (e.g., Sn-doped In2O3), composite layer films2 (e.g., TiO2/Ag/TiO2), and thin-film conducting microgrids.3 From a simplistic viewpoint, heat mirror films pass nearly all of the radiation below a given wavelength and reflect nearly all of the radiation above it; the separation point (transmission vs reflection) edge wavelength being determined by the materials and construction methods used to fabricate the heat mirror. Although in the early development stage, heat mirror films offer the potential advantage of reducing the window heat load because of their reflective properties. A simplified model of a heat mirrored cavity receiver is considered herein and used to predict cavity operating efficiency as a function of incident sun level, cavity operating temperature, and heat mirror reflectance edge position. The results are compared with those for a windowed receiver where escape of reradiated energy is prevented by a process of radiation absorption in the window, rather than by reflection back to the cavity interior as in the case of the heat mirror. Experimental data on some existing heat mirrors are summarized, and achievable performance improvements with existing heat mirror films are calculated and compared with idealized predictions. The results reported here should be considered as an initial inquiry into the usefulness of the heat mirror approach in a cavity receiver with the objective of determining whether the use of such films is sufficiently promising to warrant more detailed investigations. Though evaluations are made for three experimental heat mirrors, these heat mirrors have not been optimized for the cavity receiver application, and

Central collector solar energy receivers

Central receivers for use with power-generating equipment require compact boiler and superheater designs to effectively concentrate the solar heat input and to improve system power cycle efficiency. Solar thermal collectors employ a central receiver that must be compact to effectively utilize the high concentration ratios of sunlight energy. The demonstration of lightweight, long-life receiver designs is a technology issue that must be resolved if the concept is to be attractive for power generation. The receiver must be lightweight to minimize the cost of the supporting tower structure. Current applied aerospace technology in compact steam boilers and rocket thrust chamber designs can be directly applied to the design and fabrication of solar central receivers. This technology recently has been applied to a compact steam generator that uses liquid oxygen and natural gas, propane or fuel oil. The compact steam generator permits a 300:1 size reduction in boiler and superheater size. This paper discusses the application of the compact steam generator technology to the design and fabrication of central receivers for solar-energy-powered electrical powerplants. Receiver designs are discussed for tower-mounted applications where size and weight are important. The heat flux rates necessary for central solar receivers are nearly identical to the design hear fluxes for the compact steam generator. Fabrication of the central receiver is discussed as well as design details and applicable materials.

A cylindrical blackbody solar energy receiver

This paper discusses a design for a receiver appropriate Fora concentrating collector having potential application at moderate working temperatures (near 100°C) as well as at high temperatures (above 300°C). The receiver consists of an annular cylindrical tube with an aperture parallel to the axis of the cylinder. The aperture is illuminated by means of a focusing concentrator, such as a lens, and the radiation energy is scattered inside the cavity, absorbed by the walls and transmitted, as heat, to the working fluid flowing axially inside the annulus. To reduce radiative losses the tube is surrounded by a layer of a thermal insulator. Principal advantages of this design lie in exclusive use of commonly-available materials and current fabrication technology. Thermal losses are controlled by the configuration of the receiver assembly containing the working fluid, without the use of special surface coatings, vacuum enclosures, or other complex features. Projected performance of the collector is compared with other designs. A theoretical performance analysis is presented, and two specific examples pertiment to moderate and high-temperature applications, are discussed.

Solar-energy receiver with lithium-hydride heat storage

The results of an applied research program to experimentally evaluate a small cavity-type solar-energy receiver and integral lithium-hydride thermal-energy storage unit are described in this paper. The operational characteristics of the receiver were determined using both solar energy and an artificial heat source. Heat was transferred to boiling mercury and dry air, respectively. Both steady-state and cyclic (orbit simulation) tests were conducted with solar energy reflected into the cavity from a parabolic mirror five feet in diameter. Subsequent long-term cycling tests were performed with an electrical resistance heater installed in the absorber cavity. No apparent depletion of thermal storage capacity occurred during approximately 190 hours of cumulative operation prior to the failure of a thermocouple weld, which terminated the tests.