Richard B. Diver

Dish-Stirling Systems: An Overview of Development and Status

Dish-Stirling systems have demonstrated the highest efficiency of any solar power generation system by converting nearly 30% of direct-normal incident solar radiation into electricity after accounting for parasitic power losses [1]. These high-performance, solar power systems have been in development for two decades with the primary focus in recent years on reducing the capital and operating costs of systems. Even though the systems currently cost about

Solar Thermochemical Water-Splitting Ferrite-Cycle Heat Engines

10,000 US/kW installed, major cost reduction will occur with mass production and further development of the systems. Substantial progress has been made to improve reliability thereby reducing the operating and maintenance costs of the systems. As capital costs drop to about

A Compendium of Solar Dish/Stirling Technology

3000 US/kW, promising market opportunities appear to be developing in green power and distributed generation markets in the southwestern United States and in Europe. In this paper, we review the current status of four Dish-Stirling systems that are being developed for commercial markets and present system specifications and review system performance and cost data. We also review the economics, capital cost, operating and maintenance costs, and the emerging markets for Dish-Stirling systems.

Solar test of an integrated sodium reflux heat pipe receiver/reactor for thermochemical energy transport

Thermochemical cycles are a type of heat engine that utilize high-temperature heat to produce chemical work. Like their mechanical work producing counterparts, their efficiency depends on the operating temperature and on the irreversibility of their internal processes. With this in mind, we have invented innovative design concepts for two-step solar-driven thermochemical heat engines based on iron oxide and iron oxide mixed with other metal oxide (ferrites) working materials. The design concepts utilize two sets of moving beds of ferrite reactant materials in close proximity and moving in opposite directions to overcome a major impediment to achieving high efficiency-thermal recuperation between solids in efficient countercurrent arrangements. They also provide an inherent separation of the product hydrogen and oxygen and are an excellent match with a high-concentration solar flux. However, they also impose unique requirements on the ferrite reactants and materials of construction as well as an understanding of the chemical and cycle thermodynamics. In this paper, the counter-rotating-ring receiver/reactor/ recuperator solar thermochemical heat engine concept is introduced, and its basic operating principles are described. Preliminary thermal efficiency estimates are presented and discussed. Our results and development approach are also outlined.

Testing of a CR5 Solar Thermochemical Heat Engine Prototype

Abstract : This technology compendium, which is international in scope, presents the results of a survey on the technology status, system specifications, performance, and operation of parabolic dish solar collectors that use Stirling engines to generate electrical power. Technical information on the engines used or to be used in dish/Stirling Systems is also presented. This study uses consistent terminology to document the design characteristics of dish concentrators, receivers, and Stirling engines for electric generating applications, thereby enabling comparison of dish/Stirling technologies at both a system and component level. Development status and operation experience for each system and an overview of dish/Stirling technology are also presented.

Practical Field Alignment of Parabolic Trough Solar Concentrators

Abstract A chemical reactor for carbon dioxide reforming of methane was integrated into a sodium reflux heat pipe receiver and tested in the solar furnace of the Weizmann Institute of Science, Rehovot, Israel. The receiver/reactor was a heat pipe with seven tubes inside an evacuated metal box containing sodium. The catalyst, 0.5 wt% Rh on alumina, filled two of the tubes with the front surface of the box serving as the solar absorber. In operation, concentrated sunlight heated the front plate and vaporized sodium from a wire mesh wick attached to the other side. Sodium vapor condensed on the reactor tubes, releasing latent heat and returning to the wick by gravity. The receiver system performed satisfactorily in many tests under varying flow conditions. The maximum power absorbed was 7.5 kW at temperatures above 800°C. The feasibility of operating a heat pipe receiver/reactor under solar conditions was proven, and the advantages of reflux devices confirmed.

Screening Analysis of Solar Thermochemical Hydrogen Concepts

Sandia National Laboratories (SNL) is investigating thermochemical approaches for reenergizing CO2 and H2 O feed stocks for input to synthetic liquid hydrocarbon fuels production. Key to the approach is the Counter-Rotating-Ring Receiver/Reactor/Recuperator (CR5), a novel solar-driven thermochemical heat engine concept for high-temperature carbon dioxide and water splitting based on two-step, nonvolatile metal oxide thermochemical cycles. The CR5 integrates two reactors, recuperators, and solar receiver and intrinsically separates the product gases. The CR5 thermochemical heat engine concept and the underlying thermodynamics and kinetics have many uncertainties. While results from laboratory scale material tests are promising, they are different than what occurs in a CR5. To evaluate the potential of the CR5 we have designed and built a CR5 prototype. The overall objective of the SNL Sunshine to Petrol (S2P) project is to show a solar thermochemical pathway for the efficient production of liquid fuels from CO2 and H2 O feed stocks. To achieve the overall long-term goal of 10% efficient conversion of sunlight to petroleum, the thermochemical solar conversion of sunlight to CO needs to be 20% efficient. The short-term goal for the CR5 prototype is to demonstrate a solar to chemical conversion efficiency of at least 2%. In this paper, we present initial test results for the CR5 prototype in the 16 kWt National Solar Thermal Test Facility (NSTTF) solar furnace in Albuquerque, NM. Lessons learned from the initial tests and approaches for improving performance to achieve our goals are also presented.Copyright

Materials development for the CR5 solar thermochemical heat engine.

In this paper a new technique for parabolic trough mirror alignment based on the use of an innovative theoretical overlay photographic (TOP) approach is described. The technique is a variation on methods used to align mirrors on parabolic dish systems. It involves overlaying theoretical images of the heat collection element (HCE) in the mirrors onto carefully surveyed photographic images and adjustment of mirror alignment until they match. From basic geometric principles, for any given viewer location the theoretical shape and location of the reflected HCE image in the aligned mirrors can be predicted. The TOP approach promises to be practical and straightforward, and inherently aligns the mirrors to the HCE. Alignment of an LS-2 mirror module on the rotating platform at the National Solar Thermal Test Facility (NSTTF) with the TOP technique along with how it might be implemented in a large solar field is described. Comparison of the TOP alignment to the distant observer approach on the NSTTF LS-2 is presented and the governing equations used to draw the theoretical overlays are developed. Alignment uncertainty associated with this technique is predicted to be less than the mirror slope error.

Methodology to Assess Potential Glint and Glare Hazards From Concentrating Solar Power Plants: Analytical Models and Experimental Validation

A screening analysis was performed to identify concentrating solar power (CSP) concepts that produce hydrogen with the highest efficiency. Several CSP concepts were identified that have the potential to be much more efficient than todays low-temperature electrolysis technology. They combine a central receiver or dish with either a thermochemical cycle or high-temperature electrolyzer that operate at temperatures >600 C. The solar-to-hydrogen efficiencies of the best central receiver concepts exceed 20%, significantly better than the 14% value predicted for low-temperature electrolysis.

Status of the Advanced Dish Development System Project

The counter-rotating-ring receiver/reactor/recuperator (CR5) solar thermochemical heat engine is a new concept for production of hydrogen that allows for thermal recuperation between solids in an efficient counter-current arrangement. At the heart of the CR5 system are annular rings of a reactive solid ferrite that are thermally and chemically cycled to produce oxygen and hydrogen from water in separate and isolated steps. This design is very demanding from a materials point of view. The ferrite rings must maintain structural integrity and high reactivity after months of thermal cycling and exposure to temperatures in excess of 1100 °C. In addition, the design of the rings must have high geometric surface area for gas-solid contact and for adsorption of incident solar radiation. After performing a series of initial screenings, we chose Co0.67 Fe2.33 O4 as our baseline working material for a planned demonstration of CR5 and have begun additional characterization and development of this material. Our results to date with powders are consistent with the expectation that small particle sizes and the application of a support to inhibit ferrite sintering and enhance the chemistry are critical considerations for a practical operating device. Concurrent with the powder studies, we are using Robocasting, a Sandia-developed technique for free form processing of ceramics, to manufacture monolithic structures with complex three-dimensional geometries for chemical, physical, and mechanical evaluation. We have demonstrated that ferrite/zirconia mixtures can be fabricated into small three-dimensional monolithic lattice structures that give reproducible hydrogen yields over multiple cycles.Copyright