The Energy Information Association is the federal repository for national energy trivia- not exactly a trivial mission these days. The statistical arm of the DOE, these guys spend their days tracking everything from uranium reserves to commercial building energy consumption. They publish a report each year called the Annual Energy Review, which takes a look back at how much energy our great nation consumed, including a detailed analysis of where it came from and where it went.
One interesting chart, included below in a quasi-legible format, shows the amounts and types of raw energy feedstocks that were consumed in the production of electricity. The numbers given represent quadrillions of Btu’s (British Thermal Units). One Btu can heat one pound of water one degree Fahrenheit, and it takes roughly 1,000 Btu’s to boil a pound of water, all of which means we invested sufficient terrestrial fuel energy reserves on electricity in 2007 to boil roughly 5.1 trillion gallons of water, (or roughly the amount of water discharged by the Mississippi River into the Gulf of Mexico over a 2-3 day period).
Back to the chart: coal, for instance, provided 20.99 “quads” of energy to processes that were used to convert the stored chemical energy in the coal into electricity.
This pastel-colored complex of graphical information suggests some interesting points.
First, of the 42.1 quads of fuel energy input into electrical generating processes (the sum of energy inputs at left), 14.94 were returned as electricity. Nearly 28 quads are described as “Conversion Losses”. This results in a total national average conversion efficiency of about 35%.
Second, of the 14.94 quads of energy in electric form, about 14% or 2.09 quads, are spent to support the overall effort. 1.34 quads are expended on the grid to “push” the energy to the end user (yes, the grid more or less pushes back to a certain extent), and 0.75 quads are spent back in the power generation facilities to run supporting equipment. So, in the final accounting, 30.5% of the energy spent on electricity generation processes results in useful energy at the customer’s site.
This means that a unit of electricity generated on-site in a combined heat and power system, assuming a large percentage of the waste heat is recovered and beneficially utilized, avoids approximately 2-3 units of raw fuel energy input (on average). On-site generation can typically achieve greater than 30% electrical efficiency, and allows for recovery of waste heat to support heating and cooling.
If 50% of the commercial sector employed such a strategy (or had its combined electric and thermal needs met from district energy plants), and if 50% of the waste heat available from on-site generation were beneficially utilized, US fuel-energy consumption for electric power would drop by approximately 10%, or roughly 4.4 quads. Water consumption for power generation would also drop by roughly 40-60 billion gallons per year. I see such buildings as being the stationary equivalent of hybrid vehicles: they assemble readily available components into more efficient systems.
Capturing 50% of the commercial segment with more efficient means of generation seems like a large number, as it would mean retrofit of a vast number of buildings with new technology, the integration of which may even require retrofit of existing heating and cooling systems to enable beneficial use of recovered heat from electric generators. Its frankly a ridiculous number, but so are all of the numbers in play here.
At an assumed installed cost of $3,000/kW, however, a value that is high for today’s marketplace, a very muddy order of magnitude number for installing this type of generation is about $300 billion. To put this into perspective, in 2008, some estimates suggest that $120 billion went into renewable energy systems in the US alone, and others suggest that as much as $1.5 trillion will be invested into new electric generation capacity in this country over the next 15 years as older plants retire and demand for energy continues to grow.
By Michael Mark, PE
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