A Proposed Hybrid Geothermal-Natural Gas-Biomass Energy System for Cornell University. Technical and Economic Assessment of Retrofitting a Low-Temperature Geothermal District Heating System and Heat Cascading Solutions

Abstract

Cornell’s 2009 Climate Action Plan provides a roadmap for the Cornell University to achieve carbon neutrality by 2050. A geothermal-biomass hybrid renewable energy system has been proposed as a component of Cornell’s transformational energy plan to economically reduce its fossil fuel consumption and CO2 emissions. This paper provides an in-depth technical and economic analysis of supplementing the existing natural gas-fired combined cycle heat and power (CHP) plant with an Enhanced Geothermal System (EGS) and a torrefied biomass boiler. Cornell University’s buildings and facilities provide a representative model distributed energy system for mid-sized communities of about 30,000 people. Cornell’s location in a relatively high grade EGS region for the Northeastern U.S. provides a further opportunity to evaluate the potential of using low enthalpy geothermal resources for district heating and other direct-use applications. As a first step, the conversion of a fraction of the Cornell’s steam district heating network into a hot water distribution system was evaluated. Heat cascading solutions were implemented to enhance the utilization of renewable resources and reduce heat losses from the distribution system. Design of the district heating system and its operating parameters were optimized to obtain a minimum levelized costs of energy. An Organic Rankine Cycle (ORC) waste heat recovery unit was considered to utilize the excess thermal energy available in the summer from the EGS reservoir for generating electricity. A torrefied biomass boiler was used to supplement the heat output of EGS reservoir to meet peak winter heat demand. Proposed solutions were evaluated in terms of levelized cost of electricity (LCOE), fossil fuel consumption, and CO2 emissions.