Last week, I picked up a copy of American Scientist on the strength of a couple of interesting-looking articles, one of them relevant to our ongoing discussion of America’s energy future. It contains a graph which, at first glance, looks pretty unbelievable. The graph is title “U.S. electric industry fuel-conversion efficiency,” and it starts in 1880 with an efficiency of 50%. It reaches a peak of nearly 65%, circa 1910, before beginning a long decline to around 30%, at which level it has been from about 1960 to the present.
How can this be? Were the reciprocating steam engines and hand-fired boilers of the early power plants somehow more efficient than modern turbines?
Not at all. The efficiency of the conversion of fuel into electricity has improved, according to the graph, by about 6:1. What has been lost, though, is the efficiency gained through the use of left-over heat. In many early power plants, waste heat was distributed (as steam or hot water) through a network of pipes permitting it be be sold to local homeowners and businesses. This practice is still used in New York City, where it dates back to Edison’s day. But the use of “district heating,” as it is known, has become much less common in the U.S. than it was in the late 1800s and early 1900s. (These systems are still heavily used in some other countries, including Denmark, the Netherlands, and Finland.)
I have some questions about the efficiency numbers used in the graph. Do they properly account for seasonality?–heating is in much less demand in summer than in winter, though it is still required for hot water and for certain industrial processes. (The heat can also be used to power absorption-type air conditioners, but I doubt there were enough of these around to make much difference over the time period of the graph.) I also wonder if the graph takes into account the relatively new combined-cycle turbines, which have efficiencies close to 60%. (See GE “H System” brochure here.)
In any event, though, it does seem that there is a lot of heat being wasted by large power plants which could be used for heating and cooling applications. Why is this potentially valuable resource being wasted?
The authors (Casten & Schewe) identify two primary reasons. First, there is the trend toward building power plants a long way from cities, putting them beyond the practical range of steam or hot-water pipes. Second, there are regulatory policies that make it unprofitable or even impossible for combined heat & power systems to thrive.
The “stimulus” bill contains provisions to spend considerable money on enhancements to the electric transmission grid, partly for the purpose of bringing solar and wind power over very long distances. Maybe we’d be better off if some of this money was devoted to local networks of steam or hot water pipes, served by modest-sized gas-fired power plants offering very high total-system efficiencies. This won’t work everywhere, because of population density factors, but it could work in a lot of places. I expect that it would be provide a far more efficient ratio of capital per unit energy saved than would building wind or solar farms which require 500- or 1000-mile transmission lines to connect them to their loads.
Of course, the coalition of lawyers and environmentalists which blocks virtually all infrastructure development in this country would object to a local steam pipe network as vehemently as it objects to a long-haul transmission line.