Introduction and Background Information

In 2009, students, faculty and staff of Cornell University developed the Climate Action Plan (CAP) in response to the university’s commitment to become carbon-neutral by 2050 (Cornell University, 2014a). The CAP consists of 62 actions aimed to cut carbon emissions to zero while setting an example for other campuses and creating a living laboratory for education and research on climate, energy and sustainability. Key actions include imple- menting building standards and energy conservation initiatives, producing heat and elec-

Chapter 5. GEOPHIRES Case-Studies 80 tricity from sustainable energy sources, and offsetting unavoidable CO2 emissions with

forest management and community projects. In 2013, accelerated action was called upon by the Faculty Senate in order to become carbon neutral by 2035. A report on the updated action plan, labeled the Accelerated Climate Action Plan (ACAP), has been released in 2015 (Cornell University, 2015).

The existing energy system on campus already consists of several energy-efficient and low-carbon-intense components such as two 15 MWe natural gas turbines with heat re-

covery steam generators co-producing electricity and heat, a campus-wide district heat- ing and cooling network, a lake-source cooling system, a 1.1 MWe hydroelectric power

plant, and a 1.8 MWe solar photovoltaic (PV) array. Under the CAP, an extension of the

solar PV array is suggested to 10 MWe, as well as electricity generation from the 11.9

MWeBlack Oak Wind Farm, improvements in the district heating network by switching

from steam to hot water, and a hybrid geothermal-biomass cogeneration system (Cornell University, 2014a). The envisioned future energy system for the campus is illustrated in Figure 5.8.

Integrating energy sources in a hybrid configuration can allow us to take advantage of synergetic effects by obtaining a higher combined energy output and efficiency or lower overall levelized cost, or by offsetting weaknesses of one energy source with strengths of another. In literature, geothermal energy is most often combined with solar energy when investigating its hybrid potential (Astolfi et al., 2011; Ghasemi et al., 2014). Exam- ples of regional case-studies are a hybrid geothermal-solar system for Mexico (Lentz and Almanza, 2006), Australia (Zhou et al., 2013), and Nevada, USA (Greenhut et al., 2010). In 2012, Enel Green Power developed the first commercial-scale hybrid geothermal-solar PV plant in Nevada and recently expanded it with a concentrated solar thermal system (DiMarzio et al., 2015). Hybrid geothermal-biomass plants have also been investigated. Examples are the case-study for hybridizing an existing geothermal plant in New Zealand

Chapter 5. GEOPHIRES Case-Studies 81 (Thain and DiPippo, 2015), and in Italy (Srinivas et al., 2014). Another case-study of in- tegrating geothermal energy with biomass for generating electricity, liquefying gas (air), and providing drying, heating and cooling was conducted by Malik et al. (2015). Recently, Enel Green Power announced plans to develop the first hybrid geothermal-biomass plant in Tuscany, Italy (Enel Green Power, 2014).

Given Cornell University’s location in Upstate New York characterized by cold win- ters and correspondingly large heating demands, a hybrid geothermal-biomass cogener- ation system is recommended by the CAP to cover most of the heating load while cut- ting CO2 emissions by up to 40%. With the exception of a few isolated hot springs, no

known hydrothermal resources have been identified in Upstate New York. Therefore, the geothermal system envisioned for Cornell in this study is an Enhanced Geothermal System (EGS), although a hot sedimentary aquifer might be possible as well. The overall heat flow and average geothermal temperature gradients, while locally higher than the averages for the Northeast region, are still below the higher-grade systems in the Western U.S. Nevertheless, indigenous geothermal energy and biomass are clear choices because: (1) even a lower-grade geothermal gradient of around 25◦C/km is still acceptable when focusing on direct-use heat applications, (2) Cornell’s agriculture and forest land hold- ings are extensive. Cornell University owns 4,000 acres (1.6·107_m2_{) of idle pasture or}

crop land where bio-energy crops could be cultivated, and about 8,000 acres (3.2·107_m2₎

of forested land that could be harvested sustainably. Additional biomass resources might include campus food and solid waste, and manure from Cornell’s two dairy farms. Fur- ther (3), alternative renewable heating sources, such as solar thermal, are lower-grade and intermittent. A small modular nuclear reactor for cogeneration could be another option but permitting and gaining public acceptance in Tompkins County would be extremely difficult and hence is not considered here.

Chapter 5. GEOPHIRES Case-Studies 82

Figure 5.8 – Future energy system on the Cornell University campus as envisioned by the Climate Action Plan (Cornell University, 2014a). When fully converted to a carbon-neutral campus, a large part of the heating and electricity consumption would be supplied by a hybrid geothermal-biomass cogeneration system.

figurations shown in the works by Thain and DiPippo (2015) and Srinivas et al. (2014). In the configuration proposed by the CAP and analyzed in this study, the geothermal system covers the majority of the heating load during the cold months and generates electricity during the summer. During very cold winter days when geothermal energy alone is not sufficient, pretreated biomass is converted in a gasifier to syngas and combusted in the existing natural gas units to produce additional heat with electricity as co-product. The objective of this study was to investigate a base case scenario of the proposed hybrid geothermal-biomass system at Cornell. Using a geothermal simulation tool, cost correla- tions and resource maps for the area, all recently developed in our research group, new results on the performance of EGS in Ithaca are reported. This study continued the analy- sis in our team by providing an update and expansion of previous studies by Tester et al. (2010) and Lukawski et al. (2013). The results in this study are for a base case scenario only. Future work will look into variations on this base case to explore the sensitivity of the technical and economic system performance to several parameters including drilling

Chapter 5. GEOPHIRES Case-Studies 83 costs, discount rate, and reservoir performance.

The existing Cornell energy system is described in more detail in Section 5.3.2 where data on current energy production, consumption, efficiency, and CO2emissions are pro-

vided. The proposed geothermal-biomass cogeneration system for Cornell is presented in Section 5.3.3. Simulation parameters and results are given in Section 5.4.4. The simulation model is based on GEOPHIRES in combination with capital and O&M costs correlations, as well as energy conversion efficiencies for the biomass gasifier from literature. The over- all capital and levelized cost, energy output, and avoided CO2 emissions of the hybrid

system are estimated for two cases (small-scale pilot project and large-scale full conver- sion system). The focus of this study is on the generation of heat and electricity, not its distribution. In Section 5.3.5, the results are put in perspective by comparing them with results from previous studies on utilizing geothermal energy for Cornell (Tester et al., 2010; Lukawski et al., 2013) and with a traditional natural gas boiler system. Finally, con- clusions of this case-study are given in Section 5.3.6.