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.
Project Innovation + Advantages:
Air Squared with partners at Argonne National Laboratory, Purdue University, and Mississippi State University, will develop an advanced internal combustion engine (ICE) integrated with an organic Rankine cycle (ORC) for waste heat recovery. The ICE will use spark-assisted compression ignition (SACI) combustion, a turbulent jet ignition (TJI) fueling system, a high compression ratio, and aggressive exhaust gas recirculation to deliver a higher thermal efficiency with low emissions. Traditional internal combustion engines use the force generated by the combustion of a fuel (e.g. natural gas) to move a piston, transferring chemical energy to mechanical energy. This can then be used in conjunction with a generator to create electricity. SACI is an advanced combustion technique that uses a homogeneous mixture of fuel and air with spark assist to enable higher thermal efficiencies and lower emissions. The TJI combustion system further increases thermal efficiency by enabling reliable SACI combustion even with ultra-lean mixtures (i.e. high air to fuel ratio). The ORC design uses mostly the same components of a traditional Rankine cycle, but uses an ammonia/water mixture instead of steam, combined with a novel oil-free scroll expander.
If successful, Air Squared’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:
Innovations developed in this project could help households and businesses become more energy self-reliant and less susceptible to energy-related outages through distributed, local generation of power and heat.
Widespread adoption of high-efficiency residential CHP systems could decrease overall primary energy consumption and therefore reduce CO2 emissions associated with electricity generation by up to 10%.
Cost-effective natural gas-fueled residential CHP systems could offer consumers lower electricity and heating bills.