James B. Moreno

Three-dimensional photonic-crystal emitter for thermal photovoltaic power generation

A three-dimensional tungsten photonic crystal is experimentally realized with a complete photonic band gap at wavelengths λ⩾3 μm. At an effective temperature of 〈T〉∼1535 K, the photonic crystal exhibits a sharp emission at λ∼1.5 μm and is promising for thermal photovoltaic (TPV) power generation. Based on the spectral radiance, a proper length scaling and a planar TPV model calculation, an optical-to-electric conversion efficiency of ∼34% and electrical power of ∼14 W/cm2 is theoretically possible.

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 heat pipe testing of the Stirling Thermal Motors 4-120 Stirling engine

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

Dish/Stirling hybrid-heat-pipe-receiver design and test results

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.

Pool boiler reflux solar receiver for Stirling dish-electric systems

Stirling-cycle engines have been identified as a promising technology for the conversion of concentrated solar energy into usable electrical power. A 25 kW electric system takes advantage of existing Stirling-cycle engines and existing parabolic concentrator designs. In previous work, the concentrated sunlight impinged directly on the heater head tubes of the Stirling Thermal Motors (STM) 4-120 engine. A Sandia-designed felt-metal-wick heat pipe receiver was fitted to the STM 4-120 engine for on-sun testing on Sandias Test Bed Solar Concentrator. The heat pipe uses sodium metal as an intermediate two-phase heat transfer fluid. The receiver replaces the directly-illuminated heater head previously tested. The heat pipe receiver provides heat isothermally to the engine, and the heater head tube length is reduced, both resulting in improved engine performance. The receiver also has less thermal losses than the tube receiver. The heat pipe receiver design is based on Sandias second-generation felt-wick heat pipe receiver. This paper presents the interface design, and compares the heat pipe/engine test results to those of the directly-illuminated receiver/engine package.

Mass transport, corrosion, plugging, and their reduction in solar dish/Stirling heat pipe receivers

A 75-kW/sub t/ hybrid receiver, intended for dish/Stirling application, has been designed, fabricated, and tested. The receiver is a 6-x scale-up of our earlier successful bench-scale hybrid concept. It is a major extension of the bench-scale concept to a compact package comprising a fully-integrated solar absorber, gas-fired surface, heat pipe, combustor, and recuperator. The device is built around a sodium heat pipe having a spherical-dome solar absorber and a pin-fin-studded, cylindrical-sidewall, gas-fired surface. The combustion system uses a metal-matrix burner, with premixed air and natural gas. The recuperator is a folded-membrane design. The receiver is designed for simultaneous solar and gas-fired heating, with a nominal throughput of 75 kW/sub t/. The nominal operating (sodium vapor) temperature is 750 C. The receiver has been ground tested (gas only) at throughput power levels from 18 to 75 kW/sub t/and output temperatures up to 750 C. It was tested in four different orientations, corresponding to sun elevations of 12, 22, 45 and 80 degrees. The tests have established several landmarks at the 75 kW/sub t/ power level, including: (1) preheat of fuel/air mixtures above 600 C without preignition, (2) internal wall temperatures over 800 C with minimal warping, particularly at critical internal seals, and (3) 68% thermal efficiency including parasitics. We believe the efficiency could be boosted to 75% by the addition of an external insulation package. Our tests also verified smooth ignition, as well as the absence thermocouples, differential pressure gauges on all major flow elements, and calorimetry. Some nonfatal problems occurred during the tests, including occasional transient leakage at an internal seal, and warping of the burner matrix. Late in the scheduled tests, a hot spot developed on the heat-pipe gas-fired surface. This behavior is believed to be the result of a wick flaw; it has been seen in other heat pipes, and has been the subject of an ongoing separate effort. Design details and rationale will be presented, along with test data illustrating the behavior of the receiver, and demonstrating its efficiency.

Photonically engineered incandescent emitter

The feasibility of obtaining competitive modular bulk electric power from the Sun, which can be greatly enhanced by the use of a reflux heat pipe receiver to combine a heat engine such as Stirling with a paraboloidal dish concentrator, is discussed. Laboratory-scale experiments have been performed. Initial tests confirmed that boiling is unstable in a baseline boiler. Boiling stability was established after the addition of artificial cavities to the heated surface, and successful boiling of sodium was demonstrated for 100 h. Other stabilizing influences that may have been present are discussed. The flux and geometry closely simulated a real receiver. The results of these tests are presented, along with the design of a full-scale receiver for on-Sun testing and considerations for long-term operation.<<ETX>>

Thermophotovoltaic energy conversion using photonic bandgap selective emitters

Solar dish/Stirling systems using sodium heat pipe receivers are being developed by industry and government laboratories in the US and abroad. The unique demands of this application lead to heat pipe wicks with very large surface areas and complex three-dimensional flow patterns. These characteristics can enhance the mass transport and concentration of constituents of the wick material, resulting in wick corrosion and plugging. As the test times for heat pipe receivers lengthen, we are beginning to see these effects both indirectly, as they affect performance, and directly, in post-test examinations. We are also beginning to develop corrective measures. In this paper, we report on our test experiences, our post-test examinations, and on our initial effort to ameliorate various problems.