Sencera Energy

In 2013, centralized U.S. power plants had an average electricity generation efficiency of only 33%, wasting 67% of primary energy as heat and emitting 2 billion tons of CO2, about 38% of U.S. total emissions. Further, 6% of electricity is generally lost during transmission and distribution from the power plant to the customer. An alternative to centrally produced power is distributed generation, in which electricity is generated at the point of use. Residential combined heat and power (CHP) systems can burn natural gas to produce electricity for a home while also using the waste heat for space and water heating. The potential energy efficiency for CHP systems is more than 80% and significant adoption of such systems would enable dramatic reductions in primary energy use and concurrent CO2 emissions. However, usage of small CHP systems is not widespread because systems currently on the market are limited by high price, low efficiency, and short lifetime. The GENSETS program seeks to develop 1 kW (electric) CHP generators that have high fuel-to-electricity generation efficiency, long life, low cost, and low emissions.

Sencera Energy and Ohio University will develop a novel kinematic Stirling-Brayton hybrid engine using flexure based volume displacement in lieu of a conventional piston-cylinder Stirling engine. A Stirling engine uses a working gas housed in a sealed environment, in this case the working gas is helium. When heated by the natural gas-fueled burner, the gas expands causing a piston to move and interact with an alternator to produce electricity. As the gas cools and contracts, the process resets before repeating again. Advanced Stirling engines endeavor to carefully manage heat inside the system to make the most efficient use of the natural gas energy. The flexure-based design achieves the same function as a piston-cylinder set by simply changing the volume of the working spaces, as opposed to sliding a piston along the interior of a cylinder. The removal of pistons from the design eliminates the need for sliding seals such as piston rings or air/gas bearings, resulting in lower engine friction, less fluid flow loss and fewer dead volumes. It also lowers the potential fabrication cost compared to other heat engines. The proposed kinematic engine design provides easy coupling to existing rotary alternator designs, which allows the use of robust, mature, and cost-effective off-the-shelf alternator technologies and controllers.

If successful, Sencera’s project will facilitate development and commercialization of economical, efficient, and durable CHP systems for residential use. These advancements support progress toward ARPA-E’s overall goals as follows: