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Electricity Monthly Update

With Data for November 2016  |  Release Date: Jan. 26, 2017  |  Next Release Date: Feb. 24, 2017

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Highlights: November 2016

Key Indicators

  November 2016 % Change from November 2015
Total Net Generation
(Thousand MWh)
297,422 -1.1%
Residential Retail Price
12.75 0.3%
Retail Sales
(Thousand MWh)
272,932 -1.1%
Heating Degree-Days 418 -5.6%
Natural Gas Price, Henry Hub
2.60 21.0%
Natural Gas Consumption
700,215 -8.7%
Coal Consumption
(Thousand Tons)
48,126 -1.7%
Coal Stocks
(Thousand Tons)
172,139 -8.7%
Nuclear Generation
(Thousand MWh)
65,179 8.2%

The output range of large electric coal-fired steam turbines varies widely

Large coal-fired steam turbine generators vary widely in their range of output. To follow varying demand on electric systems over time, the collective output of generators must be able to increase and decrease rapidly. The recent significant increase in generation from renewable resources, whose output varies depending on resource availability, has added another source of variation that thermal generators need to be able to respond to. As a result, the operating ranges of these generators are becoming more important.

Source: U.S. Energy Information Administration, Form EIA-860, Annual Electric Generator Report
Note: Large means summer capacity greater than 100 megawatts (MW)

The chart above shows the output range of an important class of generators-large (>100 MW) coal-fired steam turbines--which represents about a quarter of the U.S. electric generating fleet. Recently, more of these generating units have taken on the role of marginal generators as a result of competition from natural gas-fired combined-cycle units. This means that the coal units are more often called on to increase and decrease their output.

The operating range of a generator is defined as the span between its summer peak capacity and its minimum load. Although the maximum output of a generator is typically set by thermal limits, the minimum value is often determined by technical factors such as mechanical and electrical instabilities, and by business considerations such as the higher operating costs associated with running a unit at lower levels of output. Anticipating the increasing importance of unit output ranges, EIA began collecting minimum load in 2013 in addition to peak capacity.

A key implication behind the minimum load of a generator is the ability to keep a unit operating when demand for power from that generator drops. If demand falls below the minimum load, the unit must shut down. For most conventional generators, repeated start-ups create significant maintenance challenges that increase operating costs and decrease equipment life. Large steam turbine units that have historically operated as baseload generators are particularly susceptible to cycling problems.

The ability of these systems to operate more flexibly, perhaps by increasing their operating range by lowering their minimum load, may be an important competitive advantage as generation from renewable resources increases.

Principal Contributor:

Glenn McGrath

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