Characterize the Fleet
The U.S. coal-fired fleet consists of 1,105 units with a nameplate capacity of 342.733 GW, according to the Burns & McDonnell database. Because plant age is often cited as a reason for retirement, it’s useful to examine the fleet’s age. Figure 1 illustrates the age of each unit in the database, calculated as the difference between 2011 and the year it began commercial operation.
|1. Coal fleet age distribution. Each of the 1,105 individual coal-fired units was placed into a five-year age category. For example, the category “5” represents plants that are 5 years old or less. The category “10” represents plants that are more than 5 and less than or equal to 10 years old. According to the database, one 10-MW unit built in 1925 is still on “active duty.” Source: POWER and Burns & McDonnell |
The average age of all units is 42.5 years, the MW-weighted age is 37.1 years, and the capacity factor–weighted age is 40.0 years. The MW-weighted age tells us that the average size of new power plants has been increasing over the past few decades. The capacity factor–weighted age tells us that the capacity factor of newer plants is, on average, higher. No matter how you cut the numbers, the fleet continues to age—although we shouldn’t mistake age alone as representative of the economic life of a power plant.
The database includes many useful metrics that describe interesting characteristics of the fleet, including type of coal used (Figure 2), boiler manufacturer (Figure 3), and boiler type (Figure 4).
|2. Coal fleet fuel use. Over 86% of the coal fleet burns either a bituminous or a subbituminous fuel. Source: POWER and Burns & McDonnell |
|3. Coal fleet boiler manufacturers. Source: POWER and Burns & McDonnell |
|4. Coal fleet boiler design. Source: POWER and Burns & McDonnell |
As discussed earlier, classification of combustion byproducts is currently under intense review by the EPA, and new cooling water intake structure rules were proposed in late March. We can also characterize the number of units that these two rules may impact (Figures 5 and 6) by examining metrics that I’ll return to later.
|5.Coal fleet bottom ash handling. Source: POWER and Burns & McDonnell |
|6. Coal fleet cooling water source. Source: POWER and Burns & McDonnell |
Determine Fleet Baseline Performance
Three metrics were selected to describe the performance of the current fleet of coal-fired plants. The first is the average size of plants constructed over time (Figure 7). Interestingly, the glory days for building very large central station plants was the 1960s, especially for those first supercritical plants, ranging up to 1,300 MW.
|7. Coal fleet average unit nameplate rating. The average unit rating is calculated by averaging the rating all of the units within each age category. Source: POWER and Burns & McDonnell |
Given that these large plants remain vital baseload resources, it’s no wonder that the capacity factor–weighted age of the fleet is 40 years. Although the number of plants constructed and placed into operation over the past 10 years has fallen short of predictions, their average nameplate rating increased significantly.
The average capacity factor illustrates that plants under 40 years old are the backbone of the baseload fleet; as a plant hits about the 50-year milestone, operation appears to shift to more load-following or cycling operation, as suggested by decreasing capacity factors (Figure 8). For comparison, the overall average fleet capacity factor is approximately 62%. However, 455 plants (not including recently commissioned ones, for which capacity factor information was not available) reported an annual capacity factor of 70% or higher.
|8. Coal fleet average capacity factor. The average unit capacity factor is calculated by averaging the reported capacity factor of all the units within each age category. Many of the units in the five years or less category do not have data available. A 75% capacity factor was estimated. In all categories, if capacity factor data was not available, that unit was omitted from the average. Source: POWER and Burns & McDonnell |
The average size of plants over 40 years of age is 400 MW. Average plant heat rate, as expected, generally improved in recent years (Figure 9). Plant heat rate is difficult to determine for some plants, so the Burns & McDonnell database does have a few plant heat rate gaps (81% of the plants reported). Nevertheless, the trends and averages presented here remain instructive.
|9. Coal fleet average heat rate. The average unit heat rate is calculated by averaging the reported heat rate of all the units within each age category. Heat rate data for only a single unit was available in the “five years or less” category. In the remainder of the categories, if heat rate data was not available, then that unit was omitted from the average. Source: POWER and Burns & McDonnell |