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2009 State of the Market Report

Load and Resources

of efficient pricing during peak load hours as well as in the capacity market to ensure that the system continues to maintain adequate resources.

A large share of the load in the Midwest ISO is temperature sensitive. Figure 8 illustrates the influence of weather on load by showing the heating and cooling requirements together with the monthly average load levels for 2007 to 2009.

Adjusted Degree Days

Load (GW)

08-09 %Chg

2009 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Avg. Load

-6.5% -1.7% -8.1% -8.4% -7.3% -6.7% -6.8% -14.9% -7.0% -5.8% -4.3% -5.0% -1.9%

Degree Days

  • -

    10.8%

16.6%

  • -

    13.7%

  • -

    15.4%

14.1%

5.8%

3.1%

  • -

    44.9%

  • -

    18.5%

  • -

    7.9%

15.6%

  • -

    25.2%

  • -

    5.5%

2007 2008 2009

2,400 2,000 1,600 1,200

800 400 0

Figure 8: Heating and Cooling Duration Curves Weekly Average of Four Cities in Midwest ISO, 2007 – 2009

MidAmerican and Muscatine Load

120 100 80 60 40 20 0

2009 CDD 2009 HDD Total 2007 Total 2008

The top panel shows the monthly average loads in the bars and the peak monthly load in the diamonds. The bottom panel shows monthly Heating Degree Days (“HDD”) and Cooling Degree Days (“CDD”) summed across four representative locations in the Midwest ISO.8

8

HDDs and CDDs are defined using aggregate daily temperature observations relative to a base temperature (in this case, 65 degrees Fahrenheit). For example, a mean temperature of 25 degrees Fahrenheit in a particular week in Minneapolis results in (65-25) * 7 days = 280 HDDs. To account for the relative impact of HDDs and CDDs, HDDs are inflated by a factor of 6.07 to normalize the effects on load (i.e., so one adjusted HDD will have the same impact on load as one CDD). This factor was estimated using a regression analysis.

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