Generators Continue Record Performance, Even in Recession
by Teresa Hansen, editor in chief
The recession’s impact on generators likely will be evident in the 2009 rankings, said Tom Hewson, principal at Arlington, Va.,-based Energy Ventures Analysis Inc., a firm that specializes in energy and environmental market analysis. He generated Tables 1-8 for this annual Electric Light & Power report with data from Form EIA 906, “Power Plant Report.”
“In the current economic slowdown, power demand has dropped,” Hewson said. “At the same time, gas demand outside the power sector also weakened, creating an oversupply of natural gas that was looking for a home. To move the surplus gas into the power markets, suppliers had to drop natural gas prices to displace coal. This did not have a big effect on the top 20 coal units in 2008, but it will in 2009.”
In the fourth quarter of 2008, the economy caused demand for generation to fall, so prices softened some, Hewson said. Even so, coal prices were high for most of 2008, which also allowed gas-fired generators to move above coal in the dispatch order. To view tables click here etc/medialib/elp/2009/nov_dec.Par.0922.File.dat/elpbndr.pdf
“Australia couldn’t export as much coal as in the past, which caused an increase in prices globally,” Hewson said. “Higher global prices allowed domestic producers to export more coal.”
As expected, there was little change in the top 20 coal-fired plants ranked by generation.
“When we calculate anything based on generation, there tends to be little movement,” Hewson said. “To make the top 20 list, a facility needs to have a lot of installed generating capacity, in other words, a lot of large units on one site.”
This explains why Southern Co.’s 3,346-MW Plant Scherer kept the No. 1 position. Although it generated a little less in 2008 than in 2007, it remained comfortably ahead of No. 2, Plant Bowen, another of Southern Co.’s large, coal-fired plants. Southern Co. plants landed in three of the top four positions on the generation table.
The previous No. 2 plant, Duke Energy’s Gibson Station, was down for a control project during part of 2008, Hewson said, so it fell to No. 3.
“Most large units run at high capacity factors because coal is utilized a lot,” Hewson said. “The largest coal-fired plants in the country remained high on the list. Anything greater than 2,500 megawatts is bound to be on the list.”
It’s hard to break into this list, Hewson said. Duke Energy’s Belews Creek Steam Station, Tennessee Valley Authority’s Paradise Fossil Plant and MidAmerican Energy Holdings Co.’s Jim Bridger Power Plant were the only plants on the 2008 list that did not make the 2007 list.
Xcel’s Sherburne County (Sherco) Generating Plant, FirstEnergy Corp.’s W.H. Sammis Plant and Progress Energy’s Crystal River Plant fell out of the top 20 in 2008.
Coal Capacity Factor
“When it comes to capacity factor, location is important,” Hewson said. “If you are located in a market that allows you to run your low-cost units at full capacity 24/7, you’re on the list. In several markets, units are brought down to partial loads during off-peak hours to keep a larger number of units online that will be needed the following day. For many western markets, industrial cogeneration or high industrial load areas, the coal units can run all the time they are available.”
No. 1 for coal capacity factor in 2008 was AES Hawaii, Hawaii’s only coal-fired unit, meaning it’s dispatched whenever it’s running.
“The plant was able to run year round without a scheduled outage,” Hewson said.
A greater than 100 per-cent capacity factor suggests that whatever conditions used to set the unit’s rated capacity occur only during certain times of the year. For example, some units are limited by their cooling water capacity. During times the cooling water is much colder than design, they can run at higher power output levels.
“It is unusual for a coal plant to move above 100 percent capacity factor, mainly because most coal units need to go down at least once every 12 months,” he said.
In the 2008 list, seven of the 20 plants were merchant plants. In 2007, three merchant plants made the top 20 capacity factor list. In 2008, six merchant plants made the top 10.
“This year’s merchant plant rankings have much to do with the states in which the plants are located,” Hewson said. “It helps to be located in states with high electricity prices.”
Those plants that are cogeneration units also have an advantage. Often, cogeneration facilities make money from steam sales. Money they make from electricity production is a bonus, he said.
Coal Heat Rate
“Supercritical boiler technology helps put you on the (top 20 heat rate) list,” Hewson said. “Higher-pressure steam is more energy-efficient. Usually supercritical steam pressure allows the boiler to be 2 percent more efficient than a subcritical steam cycle unit.”
Most post-combustion emissions controls consume power in their operation. This parasitic load makes the unit less energy efficient. Most units have emissions controls, so the playing field is much more level in that area than in past years, he said.
Like 2007 and other years, SCANA Corp.’s McMeekin Station, a 250-MW subcritical plant, is in the top 20 heat rate list. Its heat rate dropped from 9,485 Btu/kWhr in 2007 to 9,387 Btu/kWhr in 2008.
“I would like to ask them, “ËœWhat are you doing right?'” Hewson said. “I’m suspicious that a subcritical facility can reach a heat rate of less than 9,400. It’s like having a race between hybrids and muscle cars and then one hybrid moves to the front.”
Unit capacity factor can also be a factor. A plant’s energy efficiency improves as it reaches its maximum rated load. Therefore, units that operate at or near full capacity can achieve better efficiencies than the same design at only partial loading. It makes sense that supercritical plants dominate the heat rate list. In 2008, 14 of the top plants were supercritical, three were subcritical and three were combustion fluidized bed (CFB) plants. In 2008, 110 supercritical coal units, 1,075 subcritical coal units and 64 CFBs submitted EIA 906 forms.
The economic slowdown at the end of 2008 and high natural gas prices early that year resulted in fewer combined-cycle-generated megawatt hours from the top 20 generating plants in 2008 than in 2007. There was, however, an increase in generation overall because new combined-cycle units were brought online in 2008. These new units began displacing coal units in fourth quarter 2008 because natural gas prices declined more than coal prices.
As in past years, location played a role in the top 20 combined-cycle units by generation. In several regions (New England, California, Texas and Florida), the combination of existing generation mix and regional electricity demand means some natural gas combined-cycle units serve as baseload resources. In these regions, gas-fired combined-cycle plants run more and, therefore, make it into the top 20 generation list (see Table 4). Florida plants dominated the list in 2008, with eight of the 20 top generators residing in the state.
Similar to the coal-fired generation list, many of the top 20 combined-cycle gas-fired plants that appeared on the list in 2007 were back in 2008; 13 of the top 20 were the same. Florida Power & Light Co.’s Martin plant kept the top spot.
Combined-Cycle Heat Rate
“Plants go on and off the list all the time,” Hewson said of the top 20 heat rate plants. “It’s hard to keep track of them.”
For example, the No. 1 plant in 2007 was No. 65 in 2008. No. 2 in 2007 fell to No. 90 in 2008, and Nos. 3 and 4 dropped to Nos. 31 and 47, respectively.
Hewson cited three reasons plants make the heat rate list:
- Technology. “Efficient gas turbine technology gives plants an edge to dispatch before other gas plants,” Hewson said. “As its capacity factor improves, a plant operates in a more optimal range, efficiently using both the gas and steam turbine.”
- New plants. New plants usually use the latest technology. Newer units can create steam at a higher pressure. “It’s hard to get on this list with old technology,” Hewson said.
Location. “The list tends to be regional,” Hewson said. “It helps to be in an area where power is in high demand and natural gas is dispatched early.”
Three Mile Island, pictured here, had the highest capacity factor of any generation facility in the country in 2008. Source: NRC Photo File
While most of the plants on this list also usually have high capacity factors, the 2008 list is a little different.
“The list contains a series of plants with low capacity factors,” Hewson said, “some maybe because they just started up and weren’t online the entire year. As we slow down building new plants, the list should become more constant. These plants have a very, very good heat rate average. If you can obtain an average heat rate under 7,100 Btu/kWh, you can make the list. Seventy-one hundred is very good.”
The 2008 top 20 plants’ average heat rate was 6,968 Btu/kWhr.
Some plants on this list are also cogenerators. A cogeneration facility sometimes can have an abnormally good heat rate because of how fuel energy use and energy losses are apportioned between their power and steam products, Hewson said.
Combined-Cycle Capacity Factor
The top 20 capacity factor list contains little continuity from year to year. Most plants on this list are cogeneration facilities.
“Co-gen dominates the list,” Hewson said. “It helps to have a product you can sell outside of electricity.”
Electricity is the by-product for many of these generators.
The nation’s nuclear plants are the workhorse of its generation fleet. All nuclear plants are heavily used.
“If you own one of these plants, you run it flat out as hard as you can,” Hewson said.
When it comes to the top 20 nuclear generating units, the biggest plants are at the top of the list. The top 20 plants in 2008 are the same as in 2007.
“About the only movement seen from year to year in the generation numbers are due to planned refueling outages,” Hewson said. “Those plants that undergo refueling during the year drop down, and those that don’t move up.”
Nuclear Capacity Factor
Which plants make the capacity factor list has a lot to do with when they are brought down for refueling. Usually those in the top 20 were not refueled during the reporting year.
Four units in the 2007 top 20 showed up in the 2008 list.
The average capacity factor in 2008 was close to the 2007 average capacity factor: 96.7 percent vs. 96.4 percent. The average capacity factor for the entire nuclear fleet in 2008 was 91.1 percent, slightly higher than the 2007 average.
In addition to the tables in this article, Hewson provided tables that deal with the generators’ NOX and SO2 emissions that were not included because of space limitations. Those tables are included in the online version of this article.
The annual operating rankings are published each year in Electric Light & Power magazine’s November/December issue. To compare the 2008 report to previous years, visit http://elp.com, select “Current Issues” and then select “Past Issues.”