Environmental Engineering Reference
In-Depth Information
6,000
390
380
370
360
350
340
5,000
4,000
3,000
330
320
310
300
290
2,000
1,000
0
Source: NREL WWIS, FERC 714
FIGURE 2.1
Strongest winds blow between 9:00 p.m. and 5:00 a.m. when power demand is weakest.
When the wind increases, PSCO curtails generation from its dispatchable
sources sufficiently to accommodate the wind power. When the wind dies
down, generation from the dispatchable sources is brought back online as
needed. The process by which generation is ramped up and down at a plant
due to wind or any other factor is called
cycling.
The must-take aspect of wind generation impacts generation stacks dif-
ferently, depending on the season (Figure 2.2). The solid line indicates the
portion of total load that can be met with 1,100 MW of current wind capac-
ity if used at 100% capacity. As shown in the figure, between 8:00 a.m. and
10:00 p.m., coal generation comprises 49% (summer) to 60% (winter) of
the generation mix. Accordingly, coal facilities are less likely to be cycled
to compensate for wind generation because gas-fired generation (from
combined-cycle and combustion turbines) is sufficient to absorb the vari-
ability of wind generation. During periods of high load, it is also somewhat
easier for PSCO to sell excess power to neighboring utilities to help meet
their peak requirements.
After 10:00 p.m., the generation options are different.
Wind resources tend to be strongest at night, when generation from
coal comprises approximately 62% of the generation mix and gas-fired gen-
eration falls to 20%. If gas-fired generation is insufficient to cycle gas plants
safely, coal plants must be cycled instead. Later in the night, when coal-fired
generation is the only resource available to absorb wind power, PSCO cycles
its coal facilities. As wind energy begins to taper off around 6:00 a.m., the
cycled power plants must be ramped up because the daytime load starts
building.
