"A broad assessment of manure to power technology and
investigation of a potential wind-biogas synergy"
The purpose of this paper is to present a broad assessment of animal
manure to power technologies, and to investigate the possibility that
manure to power could be coupled with a wind generator on-farm to
produce more dispatchable power than with either technology alone.
Flexible engineering and economic models are developed to determine the
amount of energy available from manure; to characterize operation of
anaerobic digesters; and to model a farm-level generating system which
includes a wind turbine, digester, and methane storage. Maximum
electrical generating capacity from manure in the U.S. is approximately
5.4 GW, with 2.7 GW coming from manure handled as solids (incineration
or gasification), and 2.7 GW from anaerobic digestion of liquid manure.
The cost of electricity from anaerobic digestion is approximately $ 0.06
/ kWh for a farm with 700 dairy cows. Methane emissions from agriculture
account for 7% of anthropogenic methane emissions in the U.S. Therefore,
greenhouse gas reductions from anaerobic digestion, due to avoided
methane emissions from manure storage, are substantial on a per kWh
basis. A model of a digester system coupled with wind generation is
presented, and a case study is carried out for a representative hog farm
in NW Iowa. Compared to the stand-alone digester system, the coupled
system provides 65% more baseload power in summer, and 170% more during
spring. The cost of this electricity is approximately $0.075 / kWh. This
cost is comparable to a stand-alone digester system operated as a
peaking unit operated 12 hours per day.
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