APPROACHING FREE ELECTRICITY: H OW THE REAL W ORLD D IFFERS FROM THERMODYNAMIC MODELS

Abstract

As distributed generation moves from concept to reality, industrial
and institutional steam customers are realizing that they can often use
steam turbine/generator technology in their existing steam networks to
make “opportunistic” electric power and significantly reduce their an-
nual energy costs. Historically, turbines operating in this “backpressure”
mode have been assumed to have a net fuel-to-electric efficiency that is
approximately equivalent to the on-site steam boiler, because every unit
of energy removed as electricity must be replaced with a unit of heat.
Under this assumption, backpressure turbine/generators easily become
the most efficient power generation technology ever invented. While this
logic is thermodynamically true, it often breaks down in practice, where
the nuances of steam plant operation make it possible to generate elec-
tricity at an even higher efficiency with backpressure turbine/generators.
In some cases, the power produced by backpressure turbine/generators
is actually free.