Sustainable district energy integrating biomass peaking with geothermal baseload heating: A case study of decarbonizing Cornell's energy system

Many governments and institutions are advocating for higher renewable energy deployment to lower their carbon footprint and mitigate the effects of climate change. Cornell University instituted the "climate action plan" to achieve carbon neutrality, of which geothermal heat extracted from deep rocks (Earth source heat) is a critical component. This paper proposes coupling baseload geothermal heating with energy from waste biomass from Cornell's dairy farms to meet the campus' peak heating demand. The envisioned biomass peaking system, consisting of a hybrid anaerobic digestion/hydrothermal liquefaction/biomethanation process, produces renewable natural gas (RNG) for injection and storage into the natural gas (NG) distribution grid and uses NG withdrawals at times of peak heating demand. We show that 97% of the total annual peak heating demand (9661MWh) can be met using continuous RNG production using manure from Cornell's 600 dairy cows, which provides 910 x 10(6) l of RNG/year. The overall RNG system requires $8.9 million of capital investment and, assuming favorable policies, could achieve an effective levelized cost of heat (LCOH) of $32/GJ (minimum RNG selling price) and a net present value of $7.5 million after a 30-year project lifetime. Favorable policies were quantified by examining a range of incentivized prices for RNG injection ($47/MJ) and assuming wholesale utilities costs (NG withdrawals and electric imports). Selling RNG at the New York commercial NG price ($7/GJ) with utilities imports at commercial rates produces an LCOH ($70/GJ) in excess of the RNG selling price, highlighting the importance of carbon credits for financial profitability.