Economic and environmental impact assessments of a stand-alone napier grass-fired combined heat and power generation system in the southeastern US

Abstract

Napier grass, one of the high yield perennial energy crops can be grown on marginal lands with minimal inputs, but with increased soil carbon sequestration in the southeastern US. The sustainable use of Napier grass for bioenergy applications such as combined heat and power at low cost to mitigate greenhouse gas emissions needs to be investigated. In this study, an integrated life cycle assessment and techno-economic analysis approach were used to estimate the energy use, environmental emissions, and minimum selling price (MSP) of electricity and thermal heat produced from Napier grass and compared with a coal or natural gas-fired combined heat and power generation plant. The use of Napier grass as a feedstock decreased the global warming potential (GWP) of the medium-sized CHP (i.e., 13 MWe) plant by 73–92 % compared to that of a coal and natural gas-fired CHP plants. Other environmental impacts were also reduced by 24–100 %. Eutrophication was the only impact comparable to that of the coal-fired CHP plant. The energy return on investment (EROI) was around 5:1. The minimum selling price of electricity generated from the CHP plant was US$0.05–0.4 MJe−1 (US$0.13–0.18 kWh−1) considering the credits for steam production, renewable electricity production tax credit (PTC), and carbon footprint from the fossil fuel-based electricity generation. Although the pelleting of Napier grass for the CHP plant increased the cost and GHG emissions by 38% and 55% over the non-pelleted system, the pelleting process can ensure consistent quality and uninterrupted supply of the feedstock for heat and power generation.