Hi-Z Technology, Inc.

Technical Papers from 1999

Further Development of "Self-Powered Boilers"

Daniel T. Allen, Hi-Z Technology, Inc., San Diego, California, U.S.A., and
Wim Ch. Mallon, Gasunie Research, N.V. Nederlandse Gasunie, Groningen, the Netherlands

th presented at the 18 International Conference on Thermoelectrics, 29 Aug.- 2 Sept. 1999, Baltimore

Abstract
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. Full-text article available for download. (PDF)

Fabrication of MilliWatt Modules

N.B. Elsner, J.C. Bass, S. Ghamaty, C.C. Morris, N. Baker, and J.A. Bass

Abstract:
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.

Full-text article available for download. (PDF)

Milliwatt Radioisotope Power Supply for Space Applications

John C. Bass and Daniel T. Allen

presented at the 18th International Conference on Thermoelectrics, 29 Aug. - 2 Spet. 1999, Baltimore

Abstract
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.

Full-text article available for download. (PDF)

Development of Quantum Well Thermoelectric Device

(From 18th Int. Conf. On Thermoelectrics, Proceeding, ICT’99)
S. Ghamaty and N. Elsner

Abstract
The electronic and thermal properties of bulk materials are altered when they are incorporated into quantum wells. Twodimensional quantum wells have been synthesized by alternating layers of B4C and B9C in one system and alternating layers of Si and Si0.8Ge0.2 in another system. Such nanostructures are being investigated as candidate thermoelectric materials for high figures of merit (Z). The predicted enhancement is attributed to the confined motion of charge carriers and phonons in the two dimensions and separating them from the ion scattering centers.

Molecular beam epitaxy (MBE) and sputtering techniques have been used to prepare these multilayer films. Films have been deposited on single-crystal silicon substrates. The " and D properties of these films have been determined over a broad range of temperatures from 4.2K to l200K and were previously reported. The "2/D values for these P type B-C and N type SiGe films were more than a factor of 10 to 30 times higher than bulk P type B-C and N type SiGe.

Several one and two couple devices were fabricated with P-type B4C/B9C QW films and N-type bulk Bi2Te3. One of these couples produced 0.182 milliwatt at a )T of a 50/C. This device produced ten times more power than the bulk Bi2Te3 commercial material of the same dimensions and )T. Hi-Z is also producing thicker B4C/B9C films (>10 :m) on thinner Si substrates (<1 :m) to minimize thermal bypass heat losses. Successful scale up of these films for the P-leg is expected to yield a 1 cm square device that will produce ~5 Watts at a )T of 200/C. With a minimum assumption for thermal losses the device efficiency should approach 20%.

Full-text article available for download. (PDF)