Generic Assumptions

Thermal Unit Commitment

2008 SSG-WI Base Case

TSG Meeting

July 13, 2005

-   "Buckets" were agreed on by SSG-WI to classify units by fuel,
    technology, size, and vintage. The buckets were developed for
    purposes of creating generic heat rate curve and other assumptions
    necessary for GridView's thermal unit commitment logic. The buckets
    recognize significant differences in heat rate curves and other
    operating characteristics between thermal units in the West.

  ------------ ----------------- ------------------------ ---------- -------------
  **Bucket**   **Fuel**          **Technology**           **Size**   **Vintage**

  1            Gas/Oil           Steam                    \<100 MW   \<1960

  2            Gas/Oil           Steam                    \>=100 MW  \<1960

  3            Gas/Oil           Steam                    \<100 MW   \>=1960

  4            Gas/Oil           Steam                    \>=100 MW  \>=1960

  5            Gas               SCCT                                \<1985

  6            Gas               CCCT                                \<1985

  7            Gas               SCCT                     \<70 MW    \>=1985 &
                                                                     \<2006

  8            Gas               SCCT                     \>=70 MW   \>=1985 &
                                                                     \<2006

  9            Gas               CCCT                                \>=1985 &
                                                                     \<2001

  10           Gas/Oil           CCCT- Frame F                       \>=2001

  11           Gas               DT                                  \<1985

  12           Gas               DT                                  \>=1985

  13           Gas               SynCrude/Canadian Tar                
                                 Sands                               

  14           OIL               IC                                   

  15           OIL               SCCT                                 

  16           Coal              Steam                    \<100 MW   \<1960

  17           Coal              Steam                    \>=100 MW  \<1960

  18           Coal              Steam                    \<100 MW   \>=1960

  19           Coal              Steam                    \>=100 MW  \>=1960

  20           Bio/WH/Ref/Wood   Steam                                

  21           GEO               GE                                   

  22           URAN              NUCLEAR                              

  23           SUN               SL                                   

  24           PC                Steam                                

  25           Gas               SCCT                                \>=2006

  26           Gas/Oil           CCCT- Frame G            \>450 MW   \>=2008
  ------------ ----------------- ------------------------ ---------- -------------

-   When unit-specific data are available, we use that data for those
    units. When unit-specific data are not available, we use generic
    assumptions associated with the appropriate bucket.

-   California Energy Commission paper "The Use of Heat Rates in
    Production Cost Modeling and Market Modeling" was the source of
    unit-specific data for some units. See Table 1.

    -   Publicly available information

    -   Includes incremental heat rate data on 66 generating units in CA

    -   The incremental heat rate data for these units are entered into
        the database for those specific units

    -   For the buckets which contain units with data in the CEC paper,
        a CA unit was chosen as the generic unit for that bucket

        -   This unit has approximately the average size and the average
            vintage of all the units from the CEC paper that fall into
            that bucket

            -   The Platts database was used to develop generic
                assumptions which were applied to units which did not
                have publicly available unit-specific data. See Table 2.

                -   Database includes incremental heat rate data for
                    some but not all units

                -   For buckets which aren't assigned a generic unit
                    from the CEC paper, a unit is chosen from the Platts
                    database to be the generic unit for each bucket

                    -   There is sometimes sparse Platts incremental
                        heat rate data among the units in a bucket

                    -   The unit chosen as the generic for that bucket
                        has no missing incremental heat rate data in
                        Platts and has an annual average heat rate
                        closer to the SSG-WI assumption for that bucket
                        than any other plants in that bucket

                    -   Some buckets have no units with incremental heat
                        rate data in Platts. In this case, the generic
                        incremental heat rate of another bucket with
                        similar characteristics is used for that bucket

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-   Coal, geothermal, nuclear, and solar units are treated as baseload
    units and are assigned annual average heat rates, but not
    incremental heat rates

-   Generic assumptions other than incremental heat rates for thermal
    unit commitment are seen in Table 3.