This paper discusses the design of a High-G capable Radioisotope Power Supply (RPS). It provides details of the procedure that will be used when the device is assembled. A thermal model is then used to determine the heat flow in the generator and ultimately the power produced from the resulting system. Download .PDF – MilliWatt Generator Design
Thermoelectric technology has been used to reduce the logistics of field feeding. A conventional Tray Ration Heater (TRH) powered by the HMMWV, was redesigned to include a thermoelectric generator, a low power consumption DC burner, and a newly designed Power Management System (POMS). Two STRHs were fabricated and tested, and demonstrated the capability of heating rations for field feeding independent of external power generation equipment. In addition, the STRH produces surplus electricity that can be used for various needs, such as lighting, battery charging, powering radios, communication devices, etc. Most importantly, the independent operation of the STRH provides the operational flexibility to drop the field feeding system should there be a requirement for the HMMWV to accomplish another mission. Compared to powering the TRH with a 2 kW diesel generator, the integral thermoelectric generator reduces the field feeding system weight, cost, and fuel consumption, while significantly increasing system reliability. Download .PDF – A Self-Powered Field Feeding System
This paper reports the recent progress at Hi-Z technology, Inc., following from earlier work in development of milliwatt radioisotope power supplies for space applications. Several generator units have been built and tested. From the results of these tests, from ongoing design and analysis and from continued communication with DOE and with potential users of these generators at NASA, there have been suggested revisions and improvements. In this paper we discuss the most recent testing of power conversion modules and of units representing a Flight System MRPS design, and we describe two improved generator designs and their features.Download .PDF – Fabrication and Testing of Thermoelectric Modules
Ongoing experimental work and theoretical models indicate that milliwatt thermoelectric generators that operate in a sealed-off vacuum environment will be useful for long-term operation, such as the PASCAL 20 year Mars mission and the CryoScout mission. Considerations for long-term operation include out gassing of the multifoil vacuum insulation before pinch off and vaporization of the (Bi,Sb)2 (Se,Te)3 thermoelectric materials during long-term operation. Tests underway indicate the multi-foil insulation can be pre-outgassed before assembly so further outgassing in the sealed generator is minimized. Experimental data and vaporization models for a Th of 250°C thus far indicate that the small amount of vaporization of materials used in the thermoelectric module do not significantly effect the generator vacuum or the module power output. These tests and models indicate that both potential modes of degradation can be controlled and minimized. Although performance data on the generator materials only extend for several hundred hours, the good performances in a limited time, combined with an understanding of the materials behavior, indicate that milliwatt generator holds promise for providing sufficient and reliable power for space missions lasting up to 20 years. Download .PDF – Outgassing and Vaporization Considerations in MilliWatt
The pellet stove is a device that burns compressed sawdust pellets, which are a renewable energy resource. Pellet stoves provide heat with much less pollution than is experienced with other wood burning stoves. To accomplish low pollution combustion, the pellet stove employs a forced draft fan which provides excess combustion air to the burn chamber and an auger feed to dispense pellets at a controlled rate as well as a sophisticated electronic control system to achieve the proper air/fuel ratio.
The electric power requirements of the pellet stove limits their acceptance because many pellet stoves are employed in remote and rural areas with either unavailable or unreliable power. This paper describes a program funded jointly by the Renewable Energy Resources Division of the U.S. Department of Energy and the State of California under the CalTIP (California Technology Investment Partnership) Program which is currently underway to develop a self- powered pellet stove using thermoelectric technology. This paper describes this program to date. Download .PDF – Development of a Self-Powered Pellet Stove
The concept of “self-powered” appliances is one where a normally flame-heated appliance generates enough electricity also to operate its electrical components, and therefore the unit operates free from the electric grid. This would be in contrast to co-generation, in which surplus electric power is generated to be used for other functions beyond the principal purpose of the appliance. Thermoelectric generating technology is very well suited for “self-powering”. A series of “self-powered” residential-scale hydronic central heating units, often referred to as “boilers” although the circulating water does not boil, have been built with thermoelectric generating modules incorporated. These are modifications of compact, wall-mounted, highly efficient units that are a standard in the Netherlands and also popular in Great Britain and northern Germany. As well as adding the thermoelectrics, these modifications have involved conversion of the existing AC power consumers to DC wherever possible within the unit and in other ways reducing electric power demand. Each of the units built in the development phase has been more prototypic and more spartan in its electricity need. The present objective is a 22 thermal kW (75,000 BTU/hr) heating unit that runs on 55 to 60 electrical W. Twenty of these units are being built and will be field tested in 1999-2000. It appears that the case can be made that the “self-powered boiler” is marketable now in economies, such as the Netherlands, where the price gap between natural gas and electricity is wide, the prices of both are high and where comfort heating is utilized a large fraction of the year. Download .PDF – Further Development of “Self-Powered Boilers”
Hi-Z is fabricating milliWatt modules for the DOE that will be used in power supplies for NASA’s space exploration missions and the DARPA that will be used to power micro air vehicles (MAVs). Separate papers are available that describe the use of milliWatt modules in these applications. This paper deals with the factors that influence the selection of the thermoelectric materials that go into these modules, the fabrication of the modules and performance and life test data.
Download .PDF – MilliWatt Generator Design
A small thermoelectric generator is being developed for general use in space, and in particular for any of several proposed Mars atmospheric probes and surface landers that may be launched in the 2003 to 2006 time period. The design is based on using as the generator heat source and existing 1 watt radioisotope heater unit, which has already been used to provide heating alone on numerous spacecraft, including the 1997 Pathfinder/Sojourner Mars lander. The thermoelectric generating module will be bismuth-telluride alloy. The module will combine new manufacturing technology with a basic design that has a two-decade heritage of performance and lifetime data. Power output will be approximately 40 milliwatts. Important technical issues that need to be addressed in the detailed design are the mechanical integrity of the overall power supply in consideration of the impact of landing on Mars and the subsequent performance of the thermal insulation around the heat source, which is critical to delivering the output power. The power supply is intended to meet a 20-year operational lifetime. The paper describes the design status to date, and it presents the analytical approach, the testing program plan and manufacturing schedule that is needed to meet the launch dats being considered. Download .PDF -Milliwatt Radioisotope Power Supply for Space Applications
This paper presents the results of a Phase I STTR program to develop a small thermoelectric generator for use in space. The generator is designed to use the existing 1 watt radioisotope heater unit (RHU) which is currently used to keep instruments warm in space. The design and manufacture of the monolithic thermal conversion unit (TCU) is discussed as is a conceptual design of a generator which uses both the RHU and the small TCU to produce 40 mW of power at 5 volts D.C. Download the PDF
This paper describes the design of three unique thermoelectric generators developed to supply electric power in natural gas fields. The unique feature of these generators is that they do not contain their own heat source but all convert the waste heat produced by equipment already used in the gas field as the thermal power source for the generators.
The first generator described uses the difference in temperature between the hot and cold legs of the glycol natural gas dehydrator cycle to produce power for cathodic protection of the well. The second system uses waste heat from the pilot light of the gas dehydrator boiler to produce power for electronic instruments. The third system used waste heat from the gas dehydrator boiler stack to provide power for instruments, communications, and other uses around the well site.
The description of these generators includes both photographs of the prototype units and performance curves from each of the generators. Each generator has unique features and advantages which are discussed in the paper.
This paper discusses the development and test of a prototype thermoelectric generator which is designed to use the heat of existing wood fired stoves that are typically used in the area for home heating. This generator is being developed by the Royal Institute of Technology, in Sweden, to provide small amounts of power to homes in the remote northern areas of the country which are beyond the electric grid. The paper will discuss some of the aspects of the generator design, as well as the early results obtained and some of the lessons learned from the first home test site in Skerfa, Sweden, which is located near the Arctic Circle. The bismuth-telluride thermoelectric modules used in the generator are also discussed.
Hi-Z Technology, Inc. (Hi-Z) has been developing a 1 kW thermoelectric generator for class eight Diesel truck engines under U.S. Department of Energy and California Energy Commission funding since 1992. The purpose of this generator is to replace the currently used shaft-driven alternator by converting part of the waste heat in the engine’s exhaust directly to electricity. The preliminary design of this generator was reported at the 1992 meeting of the XI- ICT in Arlington, Texas. This paper will report on the final mechanical, thermal and thermoelectric design of this generator.
The generator uses seventy-two of Hi-Z’s 13 Watt bismuth- telluride thermoelectric modules for energy conversion. The number of modules and their arrangement has remained constant through the program.
The 1 kW generator was tested on several engines during the development process. Many of the design features were changed during this development as more information was obtained. We have only recently reached our design goal of 1 kW output. The output parameters of the generator are reported. Download .PDF – Performance of the 1 kW Thermoelectric Generator for Diesel Engines