Environmental Engineering Reference
In-Depth Information
used to balance wind and solar generation, they operate less efficiently. The
more wind and solar power used, the more inefficient coal facilities become.
The findings of this chapter are derived from a study conducted by
Bentek Energy. The results were published in April 2010.
1
The study uti-
lized hourly generation, fuel consumption, and emissions data from every
coal and gas generation unit in the United States with an installed capac-
ity over 25 megawatts (MW). This data, collected and provided publicly by
the U.S. Environmental Protection Agency (EPA) under the Clean Air Act
and Continuous Emission Monitoring System (CEMS) program, analyzes the
impacts of compensating for intermittent generation in the Public Service
Company of Colorado (PSCO) and Electric Reliability Council of Texas
(ERCOT) service areas.
Of the two intermittent renewable generation sources, solar generation is
not as widely used as wind generation. The impacts described in this study
focus more on wind than solar operations. Solar facilities operate only when
the sun shines and thus avoid the load limitation issues that cause coal plants
to cycle.
Wind,Gas,andCoalIntegration
Integrating wind generation with generations from other sources presents a
number of challenges. The difficulties stem fundamentally from the unpre-
dictability and intermittency of wind. Predictive models show constant
improvement but no one can be absolutely certain when wind will blow or
for how long it will continue. Historical analyses suggest that wind in the
PSCO territory blows most frequently at night. Figure 2.1 compares a wind
profile of PSCO's territory published by the National Renewable Energy
Laboratory (NREL) to PSCO's average daily load.* Wind generation tends to
peak around 4:00 a.m., then declines until about noon before slowly increas-
ing until about 8:00 p.m. The wind peak usually occurs in the early morning
hours when system demand (load) is relatively low. PSCO's load, on the other
hand, peaks between late afternoon and early evening (2:00 to 9:00 p.m.).
PSCO, like most other utilities, treats wind generation as a “must-take”
resource because of the renewable portfolio standard (RPS) mandates. In
other words, PSCO will operate its dispatchable resources (coal- and gas-
fired plants) in a manner that allows it to take as much generation from wind
as possible without allowing generations from its fossil fuel facilities to fall
below their design minimum levels.
*
The wind profile data is from work done in 2008 as part of the Western Wind Integration
Study, an ongoing project of the NREL (http://wind.nrel.gov/Web_nrel/). The PSCO load
profile represents its average daily loads for 2007 and 2008 based on its Federal Energy
Regulatory Commission (FERC) Form 714.
