Review of the solar flux distribution in concentrated solar power: Non-uniform features, challenges, and solutions

A review of sodium receiver technologies for central receiver solar power plants

Progress in heat transfer research for high-temperature solar thermal applications

Metallic Phase Change Material Thermal Storage for Dish Stirling.

Design and performance evaluation of a high-temperature cavity receiver for a 2-stage dish concentrator

A program is now underway to develop commercial power conversion systems that use parabolic dish mirrors in conjunction with Stirling engines to convert solar energy to electric power. In early prototypes, the solar concentrator focused light directly on the heater tubes of the Stirling engine. Liquid-metal heat-pipes are now being developed to transfer energy from the focus of the solar concentrator to the heater tubes of the engine. The dome-shaped heat-pipe receivers are approximately one-half meters in diameter and up to 77-kW of concentrated solar energy is delivered to the absorber surface. Over the past several years, Sandia National Laboratories, through the sponsorship of the Department of Energy, has conducted a major program to explore receiver designs and identify suitable wick materials. A high-flux bench-scale system has been developed to test candidate wick designs, and full-scale systems have been tested on an 11-meter test-bed solar concentrator. Procedures have also been developed in this program to measure the properties of wick materials, and an extensive data-base on wick materials for high temperature heat pipes has been developed. This paper provides an overview of the receiver development program and results from some of the many heat-pipe tests.

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Development of a 75-kW heat-pipe receiver for solar heat-engines

The efficient operation of a Stirling engine requires the application of a high heat flux to the relatively small area occupied by the heater head tubes. Previous attempts to couple solar energy to Stirling engines generally involved directly illuminating the heater head tubes with concentrated sunlight. In this study, operation of a 75-kW{sub t} sodium reflux pool-boiler solar receiver has been demonstrated and its performance characterized on Sandia's nominal 75-kW{sub t} parabolic-dish concentrator, using a cold-water gas-gap calorimeter to simulate Stirling engine operation. The pool boiler (and more generally liquid-metal reflux receivers) supplies heat to the engine in the form of latent heat released from condensation of the metal vapor on the heater head tubes. The advantages of the pool boiler include uniform tube temperature, leading to longer life and higher temperature available to the engine, and decoupling of the design of the solar absorber from the engine heater head. The two-phase system allows high input thermal flux, reducing the receiver size and losses, therefore improving system efficiency. The receiver thermal efficiency was about 90% when operated at full power and 800{degree}C. Stable sodium boiling was promoted by the addition of 35 equally spaced artificial cavities in the wetted absorber more » surface. High incipient boiling superheats following cloud transients were suppressed passively by the addition of small amounts of xenon gas to the receiver volume. Stable boiling without excessive incipient boiling superheats was observed under all operating conditions. The receiver developed a leak during performance evaluation, terminating the testing after accumulating about 50 hours on sun. The receiver design is reported here along with test results including transient operations, steady-state performance evaluation, operation at various temperatures, infrared thermography, x-ray studies of the boiling behavior, and a postmortem analysis. « less

Sodium reflux pool-boiler solar receiver on-sun test results

The United States Department of Energy (DOE) Solar Thermal Program, through Sandia National Laboratories (SNL), is cooperating with industry to commercialize dish-Stirling technology. Sandia and the DOE have actively encouraged the use of liquid metal reflux receivers in these systems to improve efficiency and lower the levelized cost of electricity. The reflux receiver uses two-phase heat transfer as a {open_quotes}thermal transformer{close_quotes} to transfer heat from a parabolic tracking-concentrator to the heater heads of the Stirling engine. The two-phase system leads to a higher available input temperature, lower thermal stresses, longer life, and independent design of the absorber and engine sections. Two embodiments of reflux receivers have been investigated: Pool boilers and heat pipes. Several pool-boiler reflux receivers have been successfully demonstrated on sun at up to 64 kWt throughput at SNL. In addition, a bench-scale device was operated for 7500 hours to investigate materials compatibility and boiling stability. Significant progress has also been made on heat pipe receiver technology. Sintered metal wick heat pipes have been investigated extensively for application to 7.5 kWe and 25 kWe systems. One test article has a massed over 1800 hours of on-sun operation. Another was limit tested at Sandia to 65 kWt throughput. Thesemore » devices incorporate a nickel-powder thick wick structure with condensate return directly to the wick surface. Circumferential tubular arteries are optionally employed to improve the operating margin. In addition, DOE has begun a development program for advanced wick structures capable of supporting the Utility Scale Joint Venture Program, requiring up to 100 kWt throughput. Promising technologies include a brazed stainless steel powdered metal wick and a stainless steel metal felt wick. Bench-scale testing has been encouraging, and on-sun testing is expected this fall. Prototype gas-fired hybrid solar receivers have also been.« less

T.A. Moss

Papers

Development of a 75-kW heat-pipe receiver for solar heat-engines

Sodium reflux pool-boiler solar receiver on-sun test results

Recent reflux receiver developments under the US DOE program

Reflux pool-boiler as a heat-transport device for Stirling engines - Postmortem analysis and next-generation design