Efficiency Analysis of Natural Gas Residential Micro-cogeneration Systems

Many micro-combined heat and power (micro-CHP) technologies have emerged in the residential market in the recent years. However, the selection of a particular micro-CHP system for an application and investigating the trade-offs between micro-CHP and centralized power remain a problem. The present analysis compares three micro-CHP systems on the basis of energy, exergy, and marginal efficiencies. The systems feature different energy conversion technologies: Stirling engine (WhisperGen), spark-ignition internal combustion (IC) engine (FreeWatt), and polymer electrolyte fuel cell (PEFC) (EBARA Ballard). These systems are fueled by natural gas and produce power and heat for residential applications. The analysis suggests that the IC system provides the highest energy and exergy efficiencies at higher heat use 76.7%, eta exergy = 57.2%,eta exergy =and f = 0.71), while the PEFC operates at higher energy and exergy efficiencies at lower heat use eta exergy > 29.0%, eta exergy > 32.0%, and f > 0.00). The PEFC system exhibits the greatest marginal efficiency at any heat use ( 32.0% and f > 0.00). Other important issues such as price, Anarginal> maintenance, noise, and emissions are discussed. The Stirling engine is the least expensive that requires the least maintenance. The fuel cell is the least noisy system with the least amount of emissions.