This Small Business Innovation Research Phase I project is intended to establish the feasibility of a 30% efficient electric power generator called the C-TEC, for Concentration-mode Thermoelectric Converter. To date, we have built 18 working prototypes, but have none have been suitable for efficiency measurements. The C-TEC directly generates electricity from heat using a thermally regenerated concentration gradient across an electrolyte membrane, rather than a thermal gradient across a semiconductor material, which offers the potential for high efficiency like a fuel cell, with the low cost, maintenance and long life of a thermoelectric device. Ford and NASA have researched the AMTEC, a previous concentration-mode device, since the 1980s. Research papers have used detailed theoretical models and calculations to show the potential for greater than 30% efficiency for these devices, but in practice, only 15% to 19% efficiency has ever been realized. A new design, along with a proprietary, high conductivity electrolyte material, may allow the low cost C-TEC to break the 30% efficiency barrier.
The broader impact/commercial potential of this project will be the development of low cost, high efficiency generators that can operate on any form of heat in a wide variety of applications. C-TEC generators are inherently more versatile than other technologies that require high-grade, specific fuels, such as engines (gasoline), turbines (natural gas), fuel cells (hydrogen), or solar cells (sunlight). The C-TEC makes no noise, has no moving parts and requires no maintenance, making it ideal for long-term power generation. Clean, distributed electricity provided by microCHP (Combined Heat and Power systems at less than 5 kW electrical power) enables breakthrough electrical efficiency in the home, and will be a critical technology for the widespread adoption of the electric car. The C-TEC-powered electric car will use domestic natural gas as a bridge to renewables, reducing dependence on foreign oil and massive infrastructure development costs associated with upgrades to our grid capacity. Other technologies have been proposed as prime drivers for microCHP, including fuel cells and engines, but these fall short in terms of cost and maintenance. Ultimately, the cost and versatility of the C-TEC will provide economic advantages such as fast payback to drive the adoption of new clean technologies.
based on the Concentration-mode Thermoelectric Converter (C-TEC) architecture has been demonstrated during the NSF Phase I program. The C-TEC can be used to generate electricity in many applications, including distributed co-generation, remote and portable power, waste heat recovery and solar power. Since it is thermoelectric, it can use any source of heat, including a wide variety of fuels. The C-TEC converts low value heat to high value electricity, is silent, and can operate over long periods of time with no maintenance since it has no moving parts. It uses an electrochemical concentration cell design, rather than semiconductor thermoelectric materials, to achieve the efficiency of an engine, without the noise and maintenance. NanoConversion Technologies has demonstrated the key technical design features of a high performance thermoelectric converter in a fundamentally new low-cost architecture during the Phase I program. The four main tasks that were successfully performed in Phase I included: Theoretical simulation and optimization of the C-TEC design, including the development of device performance computer models, and validation of the model using working prototypes. Demonstration and testing of C-TEC cells with high electrical cell-to-cell isolation, low-resistance cell-to-cell electrical feed-through connections and low vapor leakage rate for high efficiency. Electrode optimization for high performance, low resistance, stability, high porosity and high charge exchange current, demonstrated in a working device. Demonstration of an operating multi-cell assembly with these high efficiency design elements, plus development of rules for proper scaling of cells for high power with efficiency. The objective of the Phase I research program is to demonstrate the critical technologies that are necessary for the success of the revolutionary new type of thermoelectric converter with 30% efficiency, no moving parts, low cost and 15-year life in the Phase II program. This converter is the key technology to enable cost-effective distributed power generation such as micro-combined heat and power (micro-CHP), with enormous benefits in efficiency, cost and emissions. Several critical technologies were investigated, including the fabrication of cell assemblies with shunt-eliminating high temperature insulators, high conductivity and high porosity electrodes, in single and multi-cell stack configurations. In Phase I, NanoConversion Technologies demonstrated an operating converter unit that contains 3 series-connected cells producing open circuit voltage exceeding 3.3 V, and output power greater than 1.1 W, to fulfill the program objectives. The important Phase I accomplishments include: (1) Development of a theoretical simulation tool that incorporates the key parameters of C-TEC operation to match actual test data, and predict device performance, including efficiency. (2) Production of hundreds of cell assemblies that incorporate insulating structures with high temperature glass seals to prevent shunt currents that dramatically reduce generator power. (3) Demonstration and production of high conductivity, high porosity, thin electrodes that maintain good performance at high temperature. (4) Demonstration of a working high power density, high voltage single cell unit. (5) Demonstration of a working 3-cell stack prototype with power exceeding 1.1 W. The Phase I program was a success due to the strong adherence to a strategy of hardware testing and verification, and we plan to continue these successful strategies in Phase II. The computer model generated in the Phase I program has become a powerful tool to extract the performance parameters from our fast-turn prototype platform and identify what must be changed for an optimized design. The isolated cell has been proven to be effective in a multi-cell stack, and provides a low-cost path to the high voltage and low shunt current loss that will be the basis for high efficiency. We now have a realistic model of device efficiency that shows we can obtain greater than 25%, and with some improved yields, we will have the stacking processes to realize this in an operating device. Overall, the Phase II program moves the technology forward by combining and refining separate existing technologies that will result in a low cost, high power, high efficiency converter with a large potential impact on multiple commercial applications.
