Multi-generation Renewable Energy System for Dairy Farms: Exergy Analysis

Abstract

Exergy analyses of multi-generational micro gas turbine systems are reported for a grid-independent dairy farm in Ontario, Canada, with an aim of being environmentally benign. Onsite anaerobic digesters utilize farm waste to produce carbon neutral biogas for combustion in the micro gas turbine modules. A range of micro gas turbines coupled with absorption refrigeration units and an organic Rankine cycle are driven by the recovered waste heat to meet the cooling and electrical needs of farm sizes between 250 and 6000 cows. Exergy balances are applied to each component as well the overall system configuration, and exergy efficiencies are obtained. Small farm sizes with one absorption cooling unit are found to be more exergy efficient than large farm sizes with more than one absorption cooling unit, but the difference is less than 0.5%. Most of exergy destruction within the micro gas turbine module occurs in the combustion chamber, which contributes 79% of the exergy destruction of the system. Farm sizes between 250 and 6000 cows are observed to be capable of having their cooling and electricity needs met with micro gas turbines ranging in capacity from 100 to 1000 kW output, while exhibiting similar exergy efficiencies.