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2029 Study Results Report

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					                       DRAFT FOR TAS REVIEW

      2029 TEPPC Studies Results Report

1. Introduction
This report provides the results of production cost studies for a 2029 study year that were completed by
the Transmission Expansion Planning Policy Committee (TEPPC) of the Western Electricity Coordinating
Council (WECC) in the early part of 2010 as part of TEPPC’s 2010 Study Program. The report has five
major sections in addition to this introduction:
        Section 2, a summary of the studies completed,
        Section 3, a discussion of study conclusions and recommendations,
        Section 4, a description of the study assumptions, the study cases and key results,
        Section 5, observations on the case results that should be considered in future studies, and
        Section Error! Reference source not found.6, a comparison of the 2029 TEPPC study with the
                  Western Wind and Solar Integration Study prepared for the National Renewable
                  Energy Laboratory (NREL) by GE Energy.



2. Summary
Each year in accordance with the provisions of its Regional Transmission Expansion Planning Protocol,
TEPPC invites stakeholders to submit transmission expansion study requests. The study requests for
2009 included a request from the Western Renewable Energy Zone (WREZ) Project for a case that was
twenty years into the future, which would model a 33% penetration of renewable energy across the
WECC system. The WREZ project request was included in the 2009 TEPPC Study Program as a 2029
study case, and was scheduled to commence in late October to early November of 2009. However, due
to delays in developing the 2019 base case and the 2019 studies that were of higher priority in the 2009
Study Program, work on the 2029 studies was not initiated until December of 2009. The work on the
2029 base case continued into early 2010. When the 2010 Study Program was developed in February
and March of 2010 after receipt of new study requests, a decision was made to allot a block of study
time for additional work on the 2029 study. The 2029 study effort would continue until the end of May
2010, by which time the 2019 base case would be updated, thereby dictating a shift in the WECC Staff’s
effort onto the next stage of the 2010 Study Program.

The 2029 study turned out to be more difficult to execute than had been expected when the studies
were conceived. Under the TEPPC study methodology, a base case is built by making generation
additions without transmission additions in order to identify system congestion associated with that
new generation. Transmission expansion cases are then prepared to study congestion relief options.
This procedure is used to avoid inadvertently eliminating congestion before it is identified. In the case
of the 2029 studies, the limitations of this approach were encountered. With no new transmission
added, the large load and generation additions made to the 2019 base case to produce a 2029 case




                                                  Page 1
                                 2029 TEPPC Studies Results Report

created some significant problems in the Promod1 simulation results, including transmission constraint
violations, substantial cycling of base load generators, and increased case run time.

With the violation of the transmission constraints, the run results could not be considered a feasible
solution, so two different transmission expansion alternatives were tested. Given the limited study
time available, an entire group of lines were added under each expansion alternative, rather than
adding individual lines to look at each line’s incremental effect on the observed transmission congestion.
The first transmission alternative was referred to as incremental build-out, which used 500 kV AC and
HVDC lines already proposed by various project sponsors in the Western Interconnection. The second
alternative was a 765 kV AC overlay that would be built in lieu of the 500 kV incremental expansion
projects.

When these alternatives were run in Promod, neither of the expansion alternatives fully addressed all
the operational concerns observed in the initial run results including violation of transmission line limits
and significant coal plant cycling. This led the staff to consider the need to coordinate the transmission
violation penalty factors within the Promod data. Transmission constraint violation penalties were
increased so that wind would be spilled before a transmission constraint violation was allowed to occur,
and the three cases (base case and two expansion cases) were rerun. The increased transmission
constraint violation penalty factor provided some improvement, but cycling of base load coal plants
continued to be an unresolved concern when the overall study schedule forced termination of further
work on the 2029 study.

Because of these challenges encountered in preparation of the 2029 study, only a limited number of
cases were completed within the allotted study time. Therefore, the conclusions to be drawn from the
2029 studies are limited and tentative. However, because the study work provided experience in
studying a much heavier penetration of variable output renewable generation than previous TEPPC
studies, a number of lessons were learned and some modeling recommendations were gleaned from
the 2029 study effort that can be applied in future production cost simulation studies.

In May of 2010, as TEPPC’s 2029 studies were ending, NREL issued its report for the Western Wind and
Solar Integration Study (WWSIS). The NREL Study investigated levels renewable resource penetrations
of up to 35% within the WestConnect area (footprint) with up to a 20% penetration in the portion of the
Western Interconnection outside of WestConnect. The NREL study used a 2017 base case for this
investigation. Section 6 of this report compares the two studies to clarify the differences between them
and show the complementary nature of their results.


3. Conclusions and Recommendations

      3.1. Limited Scope of Studies
    The scope of these 2029 studies was limited to a single comparison of two potential transmission build-
    outs for incorporating 33% renewables on a WECC-wide basis. The PC1 and PC1A reference or base
    cases used as a starting point 2029 loads, 2029 generation, but only the 2019 transmission topology.
    Because of this limited scope, the 2029 studies were not able to evaluate many of the topics identified

1
 Promod IV is a production cost simulation software that models details of generating unit operating
characteristics, transmission grid topology and constraints, unit commitment/operating conditions, and market
system operations that is supplied by Ventyx.



                                                     Page 2
                               2029 TEPPC Studies Results Report

 during the study that are related to implementing a high level of renewable resource penetration. It is
 expected that more robust long-term studies will be conducted toward the end of 2010 using a new
 long-term transmission expansion tool, which will better address the transmission needs associated
 with high levels of renewable resource penetration than were possible in this limited 2029 study.

    3.2. Conclusions
In order to integrate the set of renewable resource selected to achieve a 33% penetration of renewable
resources on a WECC-wide basis, substantial transmission expansion will be required. The extent of the
transmission additions needed will be on the order of the 500 kV plus HVDC incremental build-out or
765 kV overlay transmission cases hypothesized for the 2029 studies. These two expansion plans had
9,100 miles of 500 kV AC and HVDC lines for one alternative and 6,700 miles of 765 kV lines for the other
alternative. Both alternatives helped to relieve the congestion and integrate the renewable generation
modeled in the 2029 base case. However, both expansion alternatives needed additional
enhancements to further reduce congestion. To successfully integrate the targeted level of renewable
generation, additional issues must also to be addressed that go beyond transmission expansion, these
issues include:
     The flexibility of reducing (spilling) renewable energy at times to aid system control must be
         addressed. With the renewable resources modeled as must-take the base load thermal
         generation is frequently backed off as the load decreases and preference is given to the
         renewable generation.
     The continual cycling of the coal, nuclear, and combined cycle generation observed in the 2029
         study cases is detrimental to the thermal equipment. Some of the variation seen in the studies
         may be model driven, however, care must be taken not to overlook the problem of unit cycling
         and its associated maintenance and loss of unit life costs.
     There is a timing difference, between the load ramps and the solar plant ramps in the winter
         months, that causes increased cycling of combined cycle plants. Additional flexible peaking
         capacity should be considered in the mix of resources to match the resource portfolios to
         system operational needs.

    3.3. Recommendations
    1. The conclusions to be drawn from the TEPPC 2029 studies are at best tentative due to the
       limited scope of the study. Based on the results, the production cost model did not reach an
       ideal solution for many of the study hours. The following issues should be considered for
       resolution in future studies:
            A significant amount of dump energy,
            Stranded wind generation,
            Cycling of base-load thermal generation, including nuclear plants, and
            Violated transmission constraints.

    2. The cycling behavior observed for base load generators in the 2029 studies should be more fully
       studied in future work. In particular, it is not realistic to allow renewable generation to back-off
       nuclear generation. Many of the large coal plants are also not suited for daily cycling due to
       their age and/or design characteristics. The operation of the combined cycle plants also needs
       to be evaluated as many of these were cycled off and on by the model to accommodate output
       of the renewable resources. It must be determined to what extent the observed cycling is an
       artifact of inadequate modeling. Consideration should be given in future cases to include the



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                              2029 TEPPC Studies Results Report

       cost for cycling due to increased maintenance cost and loss of life induced by unit heating and
       cooling during cycling. Adding these cycling costs will also influence the use of storage in system
       dispatch.

   3. The modeling and operation of the renewable generation should be evaluated more closely.
      The wind, solar, and part of the hydro generation was modeled in these studies as fixed, non-
      dispatchable generation with a default cost of −$1,000/MWh. Given this modeling assumption,
      the renewable generation will normally be fully utilized because it is the lowest cost resource for
      any given hour. “Fully utilized” means that each generator would operate at its “shaped”
      capacity for that hour.
          a. One possible improvement to the 2029 studies would be to reduce the amount of “must
              take” generation, especially during the light load hours. This could be optimized by
              allowing wind generation to be curtailed (or spilled) based on a price signal.
              Consideration should be given to considering the price level at which it would be best to
              spill the fixed generation, so that the default cost can be adjusted to produce more
              reasonable results.
          b. Another option would be to replace some of the base load generation with peaking
              generation that is more conducive to frequent displacement, yet responsive to the
              intermittent nature of wind generation.

   4. Another possible improvement in the 2029 cases would be investigate methods for shaping the
      energy coming from wind and solar generation using energy storage facilities that would extend
      across a full daily cycle, such as pumped storage, compressed air, or flywheel technology. The
      downside to these options is the added capital cost. In addition to shaping the renewable
      resource energy supplied to the system, demand side alternatives for reshaping the load should
      also be considered to assist in absorbing the variability of wind resource output. Dynamic
      scheduling of wind output from remote generation areas to heavy load consumption area may
      reduce the amount of net variation that must be followed, with the sending area responding to
      the local load without wind variation, and the receiving area responding to net variation of a
      much larger load in the receiving area to absorb the wind variations. The best solution probably
      lies in a combination of these approaches – more peaking flexibility, energy reshaping with
      storage, demand-side load adjustments and system control adjustments such as dynamic
      scheduling.



4. The TEPPC 2029 Study Cases

The 2029 studies were designed to evaluate the expansion of renewable generation in WECC to a 33%
penetration in total energy produced for a future 2029 study year. The 2009 Study Program described
the purpose of the 2029 studies as an “initial congestion evaluation of even greater RPS (Renewable
Portfolio Standard) development in the longer term”. The 2029 base case was also intended to be used
for the evaluation of two transmission expansion alternatives: (1) an incremental transmission
expansion approach using 500 kV AC and HVDC lines already proposed by project sponsors or (2)
building a 765 kV overlay for the Western Interconnection in lieu of the incremental projects.

Given the restricted time allocated to the 2029 studies the number of cases prepared was limited to
those shown in Table 4.1, a base case and two expansion cases as originally prepared and a repetition



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                                  2029 TEPPC Studies Results Report

of the first three cases using adjusted penalty factors for violation of transmission constraints. These six
cases are discussed in greater detail in the subsequent sections.



                                Table 4.1, List of 2029 Cases Prepared
          Case No.                                Case Description
         2029 PC1       33% WECC-wide Renewable Portfolio Standard (RPS) base case
         2029 EC1       Base Case with incremental 500kV AC/HVDC transmission build-out
         2029 EC2       Base Case with a 765kV AC high voltage overlay
         2029 PC1A      Same as PC1 above, but with increased transmission violation penalty2
         2029 EC1A      Same as EC1 above, but with increased transmission violation penalty
         2029 EC2A      Same as EC2 above, but with increased transmission violation penalty



The 2029 studies identified the need for additional transmission if the proposed set of renewable
resources were to be added to attain a 33% renewable energy target. However, there was not enough
time allotted within the study cycle to improve the initial transmission alternatives in order to produce
study cases with equivalent performance that would allow for a definitive comparison of the two
alternatives.

In addition to demonstrating a need for additional transmission to enable the use of remote resources,
the production cost simulation model revealed potential generation integration issues indicated by a
significant degree of base load generation cycling.

The cases also demonstrated the need to coordinate constraint violations penalties within the
production cost simulation, e.g., setting penalties to produce reductions in fixed generation (energy
spill) before transmission limits are overridden.

    4.1. The Base Case – 2029 PC1
The base case for the 2029 studies was designated 2029 Portfolio Case 1 (2029 PC1). The 2029 base
case used the same transmission network used in the 2019 studies conducted in 2009, but modeled a
WECC-wide 33% renewable generation contribution with additional gas-fired resources as needed to
meet the 2029 load forecast. To establish a study baseline, in accordance with the usual TEPPC study
methodology, no new transmission was added to the 2019 RPS Base Case in developing 2029 PC1.

         4.1.1. Incremental Renewable Generation
In determining the type and placement of the additional renewable resources that would be needed to
achieve a 33% WECC-wide RPS in 2029, the Studies Work Group (SWG) Resource Team utilized the work
done by the Laurence Berkley National Laboratory (LBNL) to expand the Western Renewable Energy
Zone (WREZ) Model. LBNL used the WREZ Model to derive a renewable energy allocation that

2
 The transmission limit violation penalty cost is one of the factors used in the production cost model to influence
the study solutions. When the production model must violate a constraint to reach a solution, the penalty costs
set the order that the rules and constraints are overridden.



                                                      Page 5
                               2029 TEPPC Studies Results Report

minimizes the delivered cost of energy to all 20 WECC load zones, as defined by the WREZ Model, for a
targeted level of renewables (e.g., existing RPS, 25%, 33%). The resource portfolio derived by LBNL and
used by TEPPC assumed a continuation of the Investment Tax Credit (ITC) incentives for renewables. It
is interesting to note that the renewables selected by LBNL’s WREZ model extension for a 33% WECC-
wide RPS resulted in nearly 90-100% of the WREZ resource potential being utilized in California, Oregon,
Washington, Montana, and Wyoming. LBNL also developed a renewable resource portfolio assuming
the ITC was removed, but due to time constraints TEPPC was only able to evaluate a single future
resource portfolio in the 2029 studies that assumes a continuation of the ITC.

The incremental renewables added to the 2019 PC1 RPS Base Case in order to achieve a 33% WECC-wide
RPS for 2029 PC1 are shown by resource type and WREZ zone in Figure 4.1. It is important to note that
the lack of additional resources in California is a result of the fact that California’s target of achieving
33% renewable penetration by 2020 (under a Executive Order of its Governor) was already modeled in
the 2019 RPS base case. Since this high penetration of renewables was already in the Promod dataset
for California, only minor additions of renewables were required to compensate for California load
growth. As a result most of the incremental additions made to create the 2029 PC1 33% RPS base case
occurred outside of California.

A system-wide view of installed capacity for all renewables in the 2029 PC1 case is shown in Figure 4.2,
broken down by state and province. The graph clearly shows the heavy penetration of renewable
resources in California, with about half the installed capacity located in Arizona or Wyoming, the two
states with the next highest installed capacity. The mix of resource types is also shown in Figure 4.2.
Solar resources dominate in Arizona, and are nearly a third of the California renewables. Geothermal is
also an important component in California. Wind is the primary contribution to the renewable energy
total except in Nevada where solar and geothermal are larger than the wind component. The system-
energy produced by the renewable resources is shown in Figure 4.3, again broken down by state. The
difference in capacity factor in different locations can be seen by comparing the relative sizes of the bars
between the two figures.




                                                  Page 6
                                    2029 TEPPC Studies Results Report


                   Figure 4.1, Map of Incremental Resources by WREZ
                      Added to the 2019 case to produce 2029 PC1
                      (Note: California was already at 31.7% in the 2019 Case to
                                additions were made for the 2029 base
                         which2029 Incremental Renewables by WREZcase)
          Pie Charts are Scaled According to GWh of Energy Supplied by All the Incremental Renewables in the WREZ
                                     Biomass            Wind        Solar        Geothermal          Small Hydro

                                  BC_NO
                             Gordon M. Shrum
BC_NW                                                BC_NE
 Skeena                                           Peace Canyon
                                            BC_CT
                                            Williston                                   AB_EC
                  BC_WC                                                                 Wabamun
             Kelly Lake
                              BC_SW
                              Kelly Lake                                                           AB_EA
                                                                                                   W. Brooks
                                      BC_SO
   BC_WE                               Nicola
                                                                 BC_SE                        AB_SE
  Dunsmuir                                                                                    N. Lethbridge
                                                                  Selkirk


                                                                                 MT_NW                                MT_NE
                                                                                Conrad/Bole                           Havre




                                                                                                          MT_CT
                                WA_SO
                                                                                                           Townsend
                                John Day

                                                   OR_NE
                                                   Wallula
                          OR_WE
                           Bethel                                                                                           WY_NO
                                                                                                                           Yellowcake/
                                                                     ID_SW                                                  Windstar
                                                                     Hemingway
                                                                                                                                         WY_EA
                                                                                             ID_EA                                    Laramie Rvr
                                OR_SO                                                                                 WY_EC
                                                                                             Brady
                                                                                                                      Miracle Ml
                                 Malin


                                                                                                                            WY_SO
                                                                                                                            Archer

                                                      NV_NO
                                                       Tracy
                                                                       NV_EA
                                                                      Gonder
                                                                                         UT_WE
                                                         NV_WE                           Parowan
                                                            Anaconda



                                                                            NV_SW
                                                                             Amargosa


                                                                                        AZ_NW
                                                          CA_CT                           Peacock/         AZ_NE
                                           CA_WE                 CA_NE                                                               NM_EA
                                                          Pisgah                           Hilltop          Cholla    NM_CT
                                           Antelope              Camino                                                              West Mesa
                                                                                                                      Tome
                                                                      CA_EA
                                                                      Blythe                    AZ_WE
                                                              CA_SO                               Harquahala/RedHawk/
                                                             Imperial Vly                      Mesquite/Hassayampa/Jojoba          NM_SE
                                                                                                                                   Amrad
                                                                                                      AZ_SO
                                                                   BJ_NO                              Tortolita/
                                                                                                      Saguaro                          TX
                                                                   La Rosita                                                          Caliente




                                                                     Page 7
                                       2029 TEPPC Studies Results Report


                                 Figure 4.2, Capacity for All Renewable Resources
                                     Modeled in 2029 PC1 33% RPS Base Case
                                 All Renewables Modeled in 2029 PC1 33% RPS Base Case
                                       Biomass RPS     Wind    Solar   Geothermal   Small Hydro RPS

               30,000



               25,000



               20,000
Capacity(MW)




               15,000



               10,000



                     5,000



                        0




                                                                       State

                                 Figure 4.3, Energy for All Renewable Resources
                                    Modeled in 2029 PC1 33% RPS Base Case
                                      Biomass        Wind     Solar    Geothermal       Small Hydro

                       90,000
                       80,000
                       70,000
                       60,000
       Energy, GWh




                       50,000
                       40,000
                       30,000
                       20,000
                       10,000
                             -




                                                                       State




                                                               Page 8
                                  2029 TEPPC Studies Results Report


        4.1.2. Results for 2029 PC1
The lack of transmission additions produced significant transmission congestion, violation of
transmission path rating limits and dump energy3 in the base case, 2029 PC1. Because of these
problems, the base case was unable to achieve the 33% renewable penetration target. The annual
energy figures for the base case, 2029 PC1 were:

                          Renewable share of total energy                29.6%
                          Total dump energy                          13,965 GWh
                          Total emergency energy                        522 GWh
                          Exceeded path limit energy                 15,787 GWh
                          Un-utilized4 nuclear energy                 6,859 GWh
                          Un-utilized coal energy                    44,699 GWh
                          Un-utilized wind energy                     2,231 GWh

The above energy figures for 2029 PC1 demonstrate that the incremental renewable generation in
remote sites in Wyoming, Montana, New Mexico and other areas cannot be properly integrated in the
2019 PC1 transmission network without the addition of transmission. This was expected and is
discussed in conjunction with the two transmission expansion cases, 2029 EC1 and 2029 EC2.

        4.1.3. 2029 EC1 500 kV Incremental Build-out Case
Having established that substantial transmission capacity had to be added to the 2029 PC1 base case to
produce a feasible result, two network expansion alternatives were hypothesized. The first alternative
is an incremental build-out, i.e., the set of network additions that would be the result of building over
time the 500 kV AC projects and HVDC (both +500 kV and +600 kv) projects already announced by
project sponsors in the Western Interconnection. The projects are assumed to be added one at a time,
so that at the end of 20 years the additions to the 2019 base case network would have been those
shown in Figure 4.4. The 500 kV Ac projects have the effect of completing a 500 kV overlay of the
Western Interconnection system as 500 kV lines are added in the system interior and connected to the
500 kV lines already existing in Arizona, California, British Columbia and the Pacific Northwest including
the Colstrip-Garrison-Bell/Lewiston and the Midpoint-Summer Lake ties that extend into Montana and
Idaho respectively. The 500 kV overlay is augmented by four new HVDC lines in addition to the two
HVDC lines that are part of the existing system – the Pacific DC Intertie (Celilo-Sylmar +500 kV DC) and
the Intermountain Power Project line (Intermountain-Adelanto +500 kV DC).




3
  Dump Energy represents generation that is dispatched but not utilized to serve load. Generally it is caused by
operational or transmission constraints. It is often observed in coal plants that are dispatched below their
minimum operating segment, particularly in response to heavy penetrations of renewable resources.
4
  The unutilized energy is a rough measure of generation availability versus dispatch based on capability and
outages. The values are sufficient for comparison purposes.



                                                      Page 9
                              2029 TEPPC Studies Results Report


                        Figure 4.4, Incremental Build-out Alternative
                        Using Proposed 500 kV AC and HVDC Projects




                                                                               2029 Overlay Study
                                                                             Incremental Additions
                                                                                  To 2019 Case




                                                                                    500 kV
                                                                                    HVDC




The results for the 2029 EC1 incremental build-out case showed a considerable improvement over the
2029 PC1 base case. The transmission additions helped to integrate more of the renewable resources
with less of an impact on the base load resources. The annual energy figures for the incremental build-
out case, 2029 EC1 were:

                        Renewable Share                           30.1%
                        Total Dump Energy                      3,935 GWh
                        Total Emergency Energy                   512 GWh
                        Exceeded Path Limit Energy             3,498 GWh
                        Un-utilized Nuclear Energy            10,903 GWh
                        Un-utilized Coal Energy               15,488 GWh
                        Un-utilized Wind Energy                  205 GWh




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                              2029 TEPPC Studies Results Report


   4.2. 2029 EC2 765 kV Overlay Case
In past discussions at TEPPC, interest has been expressed in considering the construction of a 765 kV
overlay in lieu of continuing with the proposed incremental expansion that would produce the network
additions shown in Figure 4.4. The network expansion shown in Figure 4.5 was used to model such a
765 kV overlay.

                            Figure 4.5, 765 kV Overlay Alternative




                                                                               2029 Overlay Study
                                                                                 765 kV Overlay




                                                                                     765 kV




Both the incremental build-out at 500 kV AC and HVDC and the 765 kV overlay were hypothesized solely
for the purpose of making a comparison in this study. While the additions were intended to provide
roughly equivalent capacity, neither was tested using power flow studies to verify their equivalence
prior to being added to the 2029 production cost studies. The results of both 2029 EC1 and 2029 EC2
showed that additional design attention would have to be given to both alternatives to make them fully
comparable (see subsection 4.4 below for further discussion).

The 765 kV overlay transmission alternative did allow additional renewable resources to reach loads;
however, conventional generation was still suppressed by the renewables. This is shown by only a
moderate decrease in dump generation as compared to the PC1 base case. The annual energy figures
for the 765 kV overlay case, 2029 EC2, were:



                                               Page 11
                                 2029 TEPPC Studies Results Report



                          Renewable Share                               30.1%
                          Total Dump Energy                          0,699 GWh
                          Total Emergency Energy                       512 GWh
                          Exceeded Path Limit Energy                 8,297 GWh
                          Un-utilized Nuclear Energy                 7,767 GWh
                          Un-utilized Coal Energy                   37,818 GWh
                          Un-utilized Wind Energy                      206 GWh



    4.3. Transmission Constraint Violation Penalties
The differences between the first three cases and the last three cases listed in Table 4.1 are significant,
because they illustrate the importance of modeling transmission constraint penalty assumptions. In the
first three cases, the transmission constraint violation penalty was set at a level that made it more
economic to pay for violating a transmission limit than forgo the opportunity to use all the available
wind generation. As a result, the simulation chose to violate the transmission constraints rather than
reduce (or spill) wind or solar energy. However, cases where the transmission path limits are exceeded
cannot be considered feasible results, since operating beyond the transmission path limits cannot be
considered acceptable or reliable.

In order for the simulation to follow reasonable operating practice, the penalty factors within the
Promod data need to be coordinated. In this case, the transmission constrain violation penalty had to
be raised in relation to the cost associated with the fixed generation in the model (wind, solar, portion
of the hydro). In the first three cases of Table 4.1, the transmission constraint violation penalty was set
at $1000/MWh. With the default cost of wind, solar, and hydro set at (-$1,000/MW) it was often more
economical to exceed the transmission limits than to use more expensive generation to serve loads.

In the three latter cases, the transmission violation penalty was raised to $6000/MWh so that fixed
energy injections were reduced before the simulation would violate transmission constraints. The effect
of making this change to the penalty factors is shown in Figure 4.6 for the original penalty factors
assumed in 2029 PC1 and in Figure 4.7 for the increased transmission penalty factors assumed in 2029
PC1A. Both figures show flows for the Montana to Northwest path as an example of the effect of
increasing the transmission limit penalty factor. This is just one of about a dozen other paths that had
frequent limit violations in 2029 PC1 while several more paths had moderate violations.

It is clear in Figure 4.7 that increasing the transmission constraint violation penalty in 2029 PC1A
corrected the flow violations that occurred in the original 2029 PC1 case. The penalty increase resolved
the majority of other violations as well, but resulted in more of the renewable energy being stranded. 5




5
  Stranded generation is excess generation that cannot be delivered to areas that could benefit economically from
that generation. Where such delivery is restricted due to insufficient transmission capacity (transmission
congestion) more expensive local generation or emergency generation is used to cover the shortfall. This
emergency generation is a measure of the load that would be un-served from the installed resources as a result of
transmission constraints.



                                                    Page 12
                              2029 TEPPC Studies Results Report


            Figure 4.6, Base Case Flows with Transmission Violation Penalty
                        Equal to Wind Energy Production Penalty

               MONTANA - NORTHWEST Flows Daily High-Low-Average 2029 PC1
  6,000
                                                                     East to West Path Limit
  5,000

  4,000

  3,000

  2,000

  1,000

       0

  (1,000)

  (2,000)




       Figure 4.7, Base Case Flows with Increased Transmission Violation Penalty

              MONTANA - NORTHWEST Flows Daily High-Low-Average 2029 PC1A
  3,000                                                                              East to West Path Limit
  2,500

  2,000

  1,500

  1,000

    500

       0

   (500)

  (1,000)

  (1,500)

  (2,000)




While the original cases with a lower transmission violation penalty cost did provide insights into the
paths where added capacity might be needed as a function of transmission limit violations, the other run
results were questionable because the cases could not be deemed feasible dispatches. The later cases
with a higher transmission violation penalty factor provide a better indication of the amount of capacity



                                                Page 13
                              2029 TEPPC Studies Results Report

needed as measured by the energy that must be curtailed in order to remain within the transmission
limits. The capacity of the transmission system is a primary factor in determining how much of the
highest quality renewable resources can be integrated into the system from remote areas of the
interconnection, particularly for wind in Wyoming and Montana.

       4.3.1. 2029 PC1A – Base Case with an Increased Transmission Violation Penalty
The changes in energy results when the increased transmission violation penalty factor was
implemented are shown in Table 4.2. The un-utilized wind energy value reported in the PC1A scenario is
more meaningful than the value reported for the PC1 scenario because it now represents the amount of
wind energy that cannot be reliably integrated into the un-expanded 2019 transmission network. This
value is of particular interest because the intent of the 2029 scenarios was to achieve a 33% WECC-wide
penetration of renewables. If all of the renewables that were added to the base case cannot be
integrated into the system, the study’s RPS targets have not been met.

                          Table 4.2, Comparison of 2029 PC1 and PC1A
             Note: Figures shown in green are decreases while those in red are increases.

                                                                            2029 PC1A Case
                                        2029 PC1 Base Case          (PC1 with Increased Transmission
                                                                            Violation Costs)
Total Dump Energy (GWh)                       13,965                             10,600
Total Emergency Energy (GWh)                   522                                 544
Exceeded Path Limit Energy                    15,787                               356
(GWh)
Un-utilized Nuclear Energy                     6,859                              3,765
(GWh)
Un-utilized Coal Energy (GWh)                 44,699                             45,265
Un-utilized Wind Energy (GWh)                 2,231                              14,832


       4.3.2. 2029 EC1A – Incremental Expansion with an Increased Transmission
              Violation Penalty
Both of the transmission expansion cases were re-run with the increased transmission violation costs,
and a comparison was made of the RPS energy produced in each case. Figure 4.8 compares 2029 PC1A
with 2029 EC1A, the incremental build-out using 500 kV AC and HVDC projects. This comparison
illustrates the amount of additional renewable energy that can be integrated into the system with the
incremental build-out transmission expansion alternative. The added transmission made it possible to
deliver coal and wind energy that was stranded in the PC1A case, backing off more expensive gas-fired
combined cycle and combustion turbine (peaking) generation. One downside of this expansion
alternative is the displacement of generation from the Palo Verde nuclear plant by surplus wind and
solar energy. The largest increases in coal generation were in Wyoming, Montana, and Colorado. It
must be remembered that this is not an increase in existing coal-fired generation, but rather the
repositioning of existing generation to its expected position on the resource stack.




                                               Page 14
                                  2029 TEPPC Studies Results Report


        Figure 4.8, Comparison of Annual Energy for 2029 PC1A and 2029 EC1A

           Annual Energy Difference: 2029 PC1A Base $6k Penalty vs. 2029
                           EC1A 500 kV AC/DC Build-out
      Conventional Hydro

         Pumped Storage

             Steam - Coal

           Steam - Other

                 Nuclear

          Combined Cycle

      Combustion Turbine

            Cogeneration

                       IC

        Negative Bus Load

             Biomass RPS

             Geothermal

         Small Hydro RPS

                    Solar

                    Wind

                       (40,000)        (20,000)             0          20,000          40,000
                                                                                        GWh




       4.3.3. 2029 EC2A – Incremental Expansion with an Increased Transmission
              Violation Penalty
Figure 4.9 provides a comparison of the 2029 PC1A base case with 2029 EC2A 765 kV overlay
transmission expansion alternative. The changes are similar to those seen in 2029 EC1A, but on a
smaller scale. The amount of transmission capacity added by the 765 kV overlay for deliveries out of
Montana and Wyoming is less than the capacity provided out of these areas by the 500 kV incremental
build-out alternative. The annual energy changes for 2029EC2A show increases in the wind and coal
generation, and once again, the nuclear generation was displaced by wind. In 2029 EC2A more of the
nuclear units were affected (Palo Verde, Diablo Canyon, and San Onofre) than in 2029 EC1A.




                                                  Page 15
                                  2029 TEPPC Studies Results Report


        Figure 4.9, Comparison of Annual Energy for 2029 PC1A and 2029 EC2A

             Annual Energy Difference: 2029 PC1A Base $6k Penalty
                        vs. 2029 EC2A 765 kV Overlay
       Conventional Hydro

          Pumped Storage

             Steam - Coal

            Steam - Other

                  Nuclear

          Combined Cycle

      Combustion Turbine

            Cogeneration

                       IC

        Negative Bus Load

             Biomass RPS

              Geothermal

          Small Hydro RPS

                    Solar

                    Wind

                       (15,000)   (10,000)   (5,000)         0     5,000      10,000      15,000
                                                                                           GWh



        4.3.1. Effect of Transmission Limit Enforcement
With the transmission limits enforced in the PC1A case, nearly 70,000 GWh of low cost generation could
not be utilized, including coal, wind, solar, nuclear, and geothermal. With the transmission expansion
applied in the EC1A and EC2A cases the un-utilized low cost generation dropped to 32,000 GWh, and
61,000 GWh, respectively. There were some tradeoffs, however, as the additional transfers led to a
different dispatch of conventional thermal generation.

    4.4. Comparison of Transmission Alternatives

        4.4.1. Renewable Energy Targets
Table 4.1 provides a comparison of the amount of renewable energy delivered in the three cases that
assumed an increased transmission limit violation penalty. Both transmission alternatives increase
renewable delivery, but the figure is higher for the incremental build-out alternative. This suggests that
the two alternatives, as hypothesized, do not have equivalent delivery capacity and that additional
studies would be needed to make them comparable for cost comparisons and reliability evaluations.




                                                   Page 16
                               2029 TEPPC Studies Results Report


      Table 4.3, Renewable Target Compared to Delivery Achieved in 2029 Cases
 2029 33% RPS Energy          Renewable Energy            Renewable Energy            Renewable Energy
        Target               Utilized in 2029 PC1A       Utilized in 2029 EC1A       Utilized in 2029 EC2A
    376,249 GWh                   350,058 GWh                367,059 GWh                 362,826 GWh
   % of RPS Target                     93%                         98%                         96%


        4.4.2. Saturated Capacity Indices
In TEPPC’s 2009 Study Program Results Report, a congestion metric, called the Saturated Capacity Index
(SCI), was used to compare transmission congestion in production cost simulation cases. Saturated
capacity hours are defined as those hours when flow on a given path is at its maximum value. The
saturated capacity hours for a given case are summed and divided by the sum of the saturated capacity
hours in a reference (or base) case to produce an SCI figure. The SCI figure provides a numerical
measure of the impact of a given action due to a change in conditions or a change in the transmission
system. In the 2009 studies it was found that, in addition to providing a single figure of merit for a given
case, by computing SCI’s for a group of transmission paths it is possible to get a sense of path flow
changes produced by differences between study cases. While there are only two transmission
expansion cases to be compared in the 2029 studies, the computation of SCIs for the two cases provides
an indication of the weakness and strengths of the two hypothesized transmission alternatives.

For the purpose of making an SCI comparison, the WECC transmission paths were grouped into five sets
of paths as shown in Figure 4.10, which includes a table showing the paths included in each grouping. In
the computation of Saturated Capacity and SCIs, only the existing lines are considered, so that the SCI
shows congestion effect on the existing system of transmission additions to the existing system. The SCI
is thus a measure of whether the additions improve congestion for each grouping of existing paths or
whether it is made congestion worse. Consideration of the loading of the transmission additions must
be done separately. Table 4.4 shows the SCIs computed for the 2029 study cases.

                        Table 4.4, SCI by Path Grouping for 2029 Cases
                                                      SCI         SCI        SCI
                             Transmission            PC1A       EC1A        EC2A
                                 Path                Base      500kV +     765 kV
                              Groupings              Case       HVDC       Overlay
                        E-W Interior                 1.00        0.60       0.64
                        Coastal                      1.00        0.52       1.29
                        Central NE-SW                1.00        2.17       0.75
                        N-S Interior                 1.00        0.20       0.30
                        SW E-W                       1.00        0.86       0.47

Examination of the SCI figures for the incremental build-out alternatives shows reduced congestion on
four of the path sets, but increased congestion on the Central NE-SW set. Examination of Figure 4.4,
shows that a large number of projects, both 500 kV AC and HVDC terminate in Southern Nevada (the Las
Vegas area) with no added capacity from the termination into California. This accounts for the doubling
of congested hours in the central axis of the system and suggests the need for added capacity into
Southern California.



                                                  Page 17
                               2029 TEPPC Studies Results Report



Examination of the SCI figures for the 765 kV overlay shows an increase in congestion in the Coastal path
set, suggesting that either more capacity is needed in the overlay in the interior to take pressure off the
existing coastal 500 kV system or that the overlay needs more capacity added to the Coastal path set. In
considering these options, it is useful to look back at Figure 4.9, which shows that the coal fired
generation dispatched in EC2A is smaller than the coal fired generation dispatched in EC1A shown in
Figure 4.8. The capacity out of Montana and Wyoming in the 765 kV Overlay (9,200 MW) is about half
the capacity added for the same area in the 500 kV + HVDC Incremental Build-out (18,000). An
additional 765 kV line in the Central NE-SW path set appears to be needed to export energy from
Montana and Wyoming, and this additional line would probably reduce congestion pressure on the
Coastal path set and increase the utilization of the existing coal resource.

                        Figure 4.10, Transmission Path Groupings for
                         Saturated Capacity Index (SCI) Comparisons
                                                             E-W Interior
                                                               MIDPOINT - SUMMER LAKE
                                                               MONTANA - NORTHWEST
                                                               BRIDGER WEST
                                                               BRIDGER - POPULOUS
                                                             Coastal
                                                               CALIFORNIA - OREGON INTERCHANGE
                                                               PACIFIC DC INTERTIE (PDCI)
                                                               SDG&E - MEXICO (CFE)
                                                               NORTHERN - SOUTHERN CALIFORNIA
                                                               ALTURAS PROJECT
                                                               LUGO - VICTORVILLE 500 KV LINE
                           No. E-W                             NORTHWEST - CANADA
                                                             Central NE-SW
                                                               PAVANT INTRMTN - GONDER 230 KV
                                                               IDAHO - SIERRA
                                                               TOT 1A
                                        Interior




                                                               INTERMOUNTAIN - MONA 345 KV
                                          N-S




                                                               SILVER PEAK - CONTROL 55 KV
                                                               IPP DC LINE
                                                               McCULLOGH - VICTORVILLE
                                                               TOT 2C
                                                             N-S Interior
                                So. E-W                        TOT 7
                                                               NORTHERN NEW MEXICO
                                                               SOUTHERN NEW MEXICO (NM1)
                                                               TOT 2A
                                                               TOT 2B2
                                                               TOT 2B1
                                                               TOT 5
                                                               IDAHO-MONTANA
                                                             SW E-W
                                                               Z4 PERKINS - BIG SANDY
                                                               WEST OF COLORADO RIVER
                                                               Z4 PEACOCK - MEAD
                                                               SOUTHWEST OF FOUR CORNERS




                                                   Page 18
                                2029 TEPPC Studies Results Report



As noted in earlier discussions in this report, additional work would be needed to make a valid
comparison of the two transmission expansion alternatives. Both need added capacity to relieve
congestion on existing paths, since both alternatives increase SCI’s on one of the path sets because of
their respective capacity inadequacies. Had there been time available for additional study work,
capacity increases could have been made to the both network expansions to tune the transmission
expansion alternatives and make them comparable. Such investigation will have to be left for future
studies.



5. Observations on Study Results
In past TEPPC studies, investigation of any given question tends to identify areas where additional study
would be warranted and to identify new questions that should be addressed. This was also true in the
2029 cases discussed above. This section covers a number of observations reached during the
evaluation of the 2029 study cases that should be considered in the design of future studies.

    5.1. Transmission Constraints
The 2029 studies clearly show that to deliver the set of resources proposed, with high wind energy
installations in Wyoming and Montana, substantial transmission expansion, on the order of the
hypothesized networks, would be needed to make use of the generation investment. The enforcement
of the transmission limits required the adoption of a $6,000/MWh penalty cost for transmission
constraint violation. In future studies the interrelationship of all the constraint violation penalties within
the data set should be coordinated, so that the actions taken within a simulation are rationally ordered.
Specifically, this study showed the need for coordination between the penalties for reducing fixed
generation and for the violation of transmission limits.

    5.2. Comparison of Transmission Alternatives
The 765 kV overlay in the EC2A case and the 500 kV build-out alternatives have weakness in relieving
system congestion. The 765 kV overlay appears to need additional facilities out of Montana and
Wyoming to reduce pressure on Coastal Paths. The 500 kV build-out alternative appears to need added
capacity between Southern Nevada and California to reduce pressure on the Central NE-SW path set.
Additional study is needed to confirm or disprove these suppositions. There may also be excess capacity
in the proposals in some path sets. Until the two networks alternatives can be seen as relatively
equivalent, comparison of their cost effectiveness will be at best tentative.

    5.3. Dump Energy
The variation in dump energy between the cases is a measure of the ability of the transmission system
to integrate new resources. The majority of the dump energy in the 2029 cases comes from coal plants
in Montana and Wyoming. It is likely associated with minimum generation problems where the
dispatchable units have been backed down to minimum, but the sum of minimum dispatchable
generation and must-take resources (hydro, wind, solar, and must-run thermal ) is in excess of the local
load plus the energy exports allowed by transmission constraints. Under such circumstances, the only
solution for the model is to dump energy, i.e., create a fictitious load to consume the unusable energy.
Ramping limits are also factors that contribute to dump energy. Table 5.1 compares the dump energy



                                                  Page 19
                               2029 TEPPC Studies Results Report

in the three cases with increased transmission violation penalties. The incremental build-out case
makes the greatest reduction in dump energy, but both alternatives appear to need additional
transmission capacity.

               Table 5.1, Comparison of Dump Energy for 2029 Cases (GWh)
                                       PC1A             EC1A              EC2A
                 Dump Energy           10,600           4,090             8,953

In the 2029 cases, nuclear and coal fueled generators are modeled with operating ranges between
minimum and maximum output levels that can lead to unrealistic results. Normally, this flexibility is
desirable as there are times that base load units must be backed off due to low loads (such as weekends
and holidays). The 2029 33% renewable cases over-utilize this flexibility because of an abundance of
“must take” wind generation during many light load hours. One solution would be to limit the flexibility
of the base load nuclear and coal generation by setting the minimum output levels closer to the
maximum levels. This would reduce the amount of cycling, but increase the amount of dump energy.
Figure 5.1 below shows a hypothetical before and after dispatch to illustrate a dump energy situation.
In Solution I, the coal and nuclear flexibility is as modeled while in Solution II the flexibility has been
removed.

The generation that extends above the load line in Solution II is dump energy. Although the chart infers
that this is made up of wind and hydro, in reality the generation with the highest cost will be reduced
(i.e. coal for the dump hours shown). One problem with limiting unit flexibility is that the dump energy
can mask input assumptions problems. Another issue with limiting the operating flexibility of the base-
load units is that the minimum generation setting is also the unit start-up threshold. Instead of
modeling a gradual startup, the units with high minimum settings would need to start near their
maximum capacity.

Dump energy indicates dispatch problems with hydro and thermal generation (including biomass and
geothermal). Dump energy occurs when:
            a. the amount of “must take” generation exceeds the area load,
            b. and there is insufficient available transmission to export,
            c. or the surplus resources are not economically viable to displace other generation.
To reduce dump energy, the amount of “must take” generation must be reduced or the transmission
constraints must be mitigated.




                                                 Page 20
                                      2029 TEPPC Studies Results Report


          Figure 5.1, Hypothetical Dispatches to Illustrate Dump Energy Issues
             4500
                                            Hypothetical Dispatch Solution I
             4000


             3500


             3000                                                                                Other
                                                                                                 Hydro
             2500                                                                                Wind
                                                                                                 Solar
             2000                                                                                Coal
                                                                                                 Nuclear
             1500
                                                                                                 Geothermal
                                                                                                 Demand
             1000


              500


                0
                    1   3   5   7   9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47


             4500
                                           Hypothetical Dispatch Solution II
             4000


             3500


             3000                                                                                Other
                                                                                                 Hydro
             2500                                                                                Wind
                                                                                                 Solar
             2000                                                                                Coal
                                                                                                 Nuclear
             1500
                                                                                                 Geothermal
                                                                                                 Demand
             1000


              500


                0
                    1   3   5   7   9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47




    5.4. Cycling of Base Load Generation
For this discussion, unit cycling is described as the movement of base load (mostly coal) generation
between a minimum capacity level and a maximum capacity level over a specified period. The design
assumption for most base load generation is that it will come on line and operate at or near its
maximum capacity in most hours. Since the units were not designed for frequent cycling, there is the
concern that frequent cycling will result in damage to units caused by the increased thermal stress on
the facilities due to repeated heating and cooling.




                                                           Page 21
                                2029 TEPPC Studies Results Report

Unit cycling occurs in the hourly dispatch of resources as Promod optimizes the load/resource balance
to reach the least-cost solution across the interconnection. Figure 5.2 shows an example of cycling for a
large coal unit (Colstrip 3 in Montana) in the PC1A case. This base-load unit is regularly displaced by
wind generation. It should be noted that a few of the shut-downs are scheduled outages and simuation
of forced outages that have nothing to do with the hourly dispatch.

                  Figure 5.2, Cycling of Colstrip3 in 2029 PC1A – Base Case
       MW                         Colstrip3 Daily Max - Min - Average
      900


      800


      700


      600


      500


      400


      300


      200


      100


        0
        1-Jan   1-Feb   1-Mar   1-Apr   1-May   1-Jun   1-Jul   1-Aug   1-Sep   1-Oct   1-Nov   1-Dec




Figure 5.3 shows the operation of one of the nuclear plants (WNP2) in the PC1A case. The cycling is
again a function of the economic dispatch and the abundance of renewable generation operating in a
must-take mode.

      Figure 5.3, Cycling of Washington Nuclear Plant 2 in 2029 PC1A – Base Case
       MW                           WNP2 Daily Max - Min - Average
     1400



     1200



     1000



      800



      600



      400



      200



        0
        1-Jan   1-Feb   1-Mar   1-Apr   1-May   1-Jun   1-Jul   1-Aug   1-Sep   1-Oct   1-Nov   1-Dec




Figure 5.4 is the same chart as Figure 5.3 plotted from the EC1A case where incremental building of 500
kV AC and HVDC transmission was added.




                                                  Page 22
                                  2029 TEPPC Studies Results Report


              Figure 5.4, Cycling of Washington Nuclear Plant 2 in 2029 EC1A
            With Incremental Build-out of 500 kV and HVDC Transmission Added
       MW                       WNP2 Daily Max - Min - Average 2029 EC1A
     1400



     1200



     1000



      800



      600



      400



      200



        0
        1-Jan   1-Feb   1-Mar     1-Apr   1-May   1-Jun   1-Jul   1-Aug   1-Sep   1-Oct   1-Nov   1-Dec




The cycling here is worse because the additional transmission makes more of the wind energy
deliverable. This in turn displaces more of the nuclear generation. The plot of unit output for Colstrip 3
in Figure 5.5 shows a slight improvement in operation, but still significant cycling.

                      Figure 5.5, Cycling of Colstrip 3 in 2029 EC1A
                With Incremental Build-out of 500 kV AC and HVDC Added
       MW                  Colstrip3 Daily Max - Min - Average 2029 EC1A
      900


      800


      700


      600


      500


      400


      300


      200


      100


        0
        1-Jan   1-Feb   1-Mar     1-Apr   1-May   1-Jun   1-Jul   1-Aug   1-Sep   1-Oct   1-Nov   1-Dec




    5.5. Dispatch Examples
The aggregate dispatch for generation for a ten day period in the spring is shown in Figure 5.6. The 10-
day snapshot illustrates how the wind and solar energy fits into the hourly dispatch with occasional
displacement of base-load resources. The lower portion of the figure shows area LMPs for the same
period. Here the solar energy in Arizona appears to be directly linked to the APS LMP, and the Alberta
(AESO) LMP reflects the operation of combined cycle and combustion turbine generation. The variable
nature of the wind energy is evident in this dispatch series. Note also that the flexibility of the
combined cycle generation is used to integrate the wind and solar.




                                                    Page 23
                                            2029 TEPPC Studies Results Report


                                 Figure 5.6, EC1A – WECC 10 Day Hourly - Spring
 180,000
                                                                                                                                         Combustion Turbine

 160,000                                                                                                                                 Steam - Other

                                                                                                                                         Combined Cycle
 140,000
                                                                                                                                         Other
 120,000                                                                                                                                 Solar

 100,000                                                                                                                                 Wind

                                                                                                                                         Small Hydro RPS
  80,000
                                                                                                                                         Geothermal
  60,000                                                                                                                                 Biomass RPS

                                                                                                                                         Hydro+PS
  40,000
                                                                                                                                         Steam - Coal
  20,000                                                                                                                                 Nuclear

      0                                                                                                                                  Demand

     5/12/2029   5/13/2029   5/14/2029   5/15/2029   5/16/2029   5/17/2029   5/18/2029   5/19/2029   5/20/2029    5/21/2029              Dump




     100                                                                                                                      Area LMP

                                                                                                                                  AESO

      50                                                                                                                          APS
                                                                                                                                  BCTC
                                                                                                                                  LDWP
       0
                                                                                                                                  NWMT
                                                                                                                                  PACW
     -50                                                                                                                          PG&E_VLY


    -100




                                   Figure 5.7, EC1A – WECC 10 Day Hourly - Fall
 180,000
                                                                                                                                         Combustion Turbine

 160,000                                                                                                                                 Steam - Other

                                                                                                                                         Combined Cycle
 140,000
                                                                                                                                         Other
 120,000                                                                                                                                 Solar

 100,000                                                                                                                                 Wind

                                                                                                                                         Small Hydro RPS
  80,000
                                                                                                                                         Geothermal
  60,000                                                                                                                                 Biomass RPS

                                                                                                                                         Hydro+PS
  40,000
                                                                                                                                         Steam - Coal
  20,000                                                                                                                                 Nuclear

      0                                                                                                                                  Demand

     11/1/2029   11/2/2029   11/3/2029   11/4/2029   11/5/2029   11/6/2029   11/7/2029   11/8/2029   11/9/2029   11/10/2029              Dump




    100

                                                                                                                                  AESO

     50                                                                                                                           APS
                                                                                                                                  BCTC
                                                                                                                                  LDWP
      0
                                                                                                                                  NWMT
                                                                                                                                  PACW
    -50                                                                                                                           PG&E_VLY


   -100



Figure 5.7 shows the aggregate dispatch for 10-day period in the fall. Note that the load pattern in the
fall has a double daily peak compared to the single peak typical of spring and summer. The second peak,
usually the highest of the day, occurs as people return home in the late afternoon/early evening. This
second peak also occurs after the ramp-down of the solar generation output. The hydro is already



                                                                       Page 24
                              2029 TEPPC Studies Results Report

following the load and combined cycle generation must ramp up to fill in the gap. The LMP’s reflect the
wind in NWMT, the solar in APS, and the dispatch of combustion turbines to meet some of the steep
load ramps.
                                                              Figure 5.8, Typical Resource Stack
                                                              1000
        5.5.1. Resource Stack in Dispatch
                                                                                   CT Peaking
                                                              900
The production cost simulation uses the available
                                                                                 CC above min
resources to meet the load requirements for each hour of
                                                              800
                                                                                   Economy
a study case. A typical resource stack is represented in                           Imports
Figure 5.8 showing available generation ordered by            700
                                                                                  Hydro above
commitment type and cost. The dispatch level will match                               min

the load requirement for the sample hour. If the load is      600

500 MW then the unit dispatch will only include the                              Coal above min
                                                              500
resources up to “Coal above min”.
                                                              400                 Must-take
                                                                                  Renewable
The dispatch decisions made by a production cost
simulation depend on the data inputs needed to model          300
                                                                                   Minimum
                                                                                    Hydro
the dispatch order. One of the primary dispatch factors is
                                                              200                Minimum Base
the cost, which is derived in various ways. The hydro,                            Load Coal &
wind, and solar generation are modeled with no fuel cost,     100
                                                                                      Gas

making these the lowest cost resources, thereby                                     Nuclear
modifying the stack order.                                      0




    5.6. Integration of Variable Generation
In much of the above discussion, the focus has been on the need for additional transmission to integrate
the set of renewable resources selected to achieve a 33% penetration of renewable resources on a
WECC-wide basis. However, the integration of resources goes beyond transmission to the flexibility of
the system to make adjustments to compensate for the variability of wind and solar renewable
resources.

        5.6.1. Load net Wind and Solar (LNWS) Shape
The primary sources of variation in the 2029 cases are caused by movement in both the load, and of
wind and solar generation. The daily, weekly, and seasonal patterns of load variation are well
understood and have been used in the past to assemble a fleet of resources that were designed to
follow load variation. To understand the additional variability introduced by wind and solar resource
patterns it is useful to examine the load net of wind and solar (LNWS) shape, i.e. the load with the wind
and solar inputs subtracted. The LNWS shape for a balancing area, subregion, or WECC as a whole is the
entities hourly load minus its hourly aggregated solar generation minus its hourly aggregated wind
generation. In other words, for any given hour the difference between an entities load shape and its
LNWS shape is its wind and solar generation for that hour. The LNWS shape is the load which the
dispatchable resourses must follow, so it instructive to look at the LNWS shape when investigating over
generation and excessive ramping/cycling problems. Figure 5.9 shows the LNWS and load shapes in the
2029 PC1 scenario for the California South sub-region from March 28th to March 30th, with the LNWS
shape being much more irregular.




                                                Page 25
                              2029 TEPPC Studies Results Report


           Figure 5.9, LNWS California South in 2029 PC1 case – March 28-30




The LNWS shapes can be very different from the load shapes where there is a high penetration of
variable resources. In such conditions, the LNWS shapes tend to have more variation in them, and they
tend to be less predictable than their corresponding load shapes.

        5.6.2. Hourly Variation Duration Plot (HVD plot)
An hourly variation duration plot (HVD) graphically displays the amount of variation that is present in an
hourly shape. An HVD plot is derived from an hourly shape by calculating the change in the hourly
shape from hour to hour and then sorting the result from the largest change to the smallest change. For
example, if the hourly value at 4 a.m. is 300 MW, at 5 a.m. is 400 MW, and at 6 a.m. is 320 MW, then the
change in the hourly shape from 4 to 5 a.m. is 100 MW and from 5 to 6 a.m. is 80 MW.

The HVD plot in Figure 5.10 compares the movement in the dispatch of all the combined cycle plants in
AZ-NM-NV of three 2029 scenarios: PC1A, EC1A, and EC2A. This HVD plot shows that the addition of
transmission in the expansion cases reduces the amount of movement in the dispatch of the combined
cycle plants in AZ-NM-NV.




                                                 Page 26
                               2029 TEPPC Studies Results Report


               Figure 5.10, Hourly Variation Duration Plots – 2029 Profiles




HVD plots can be used to compare the movement in the dispatch of a single unit or a group of units
between multiple scenarios or between a scenario and a historic year. HVD plots can also be used to
compare the amount of variation in load shapes and LNWS shapes. HVD plots are used for this purpose
in the discussion that follows.

       5.6.3. The 2029 Load and LNWS Shapes
In order to better understand how transmission expansion influences the amount of variation in the
system, HVD plots for LNWS shapes were calculated for three hypothetical transmission situations using
the load, wind, and solar profiles found in the 2029 case. These three hypothetical transmission
situations are labeled WECC, sub-region, and BA (Balancing Area). A description of each hypothetical
transmission situation is given in Table 5.2.

           Table 5.2, Hypothetical Transmission Situations for 2029 Profiles
                 Hypothetical
                 Transmission                         Description
                   Situation
                                 There is sufficient transmission to deliver power
                    WECC
                                 between any two nodes in the WECC.
                                 There is sufficient transmission to deliver power
                  Sub-Region     between any two nodes in any sub-region but no
                                 power can be delivered between sub regions.
                                 There is sufficient transmission to deliver power
                      BA         between any two nodes in any BA but no power can
                                 be delivered between BAs.




                                                Page 27
                               2029 TEPPC Studies Results Report

The hypothetical transmission situation labeled WECC indicates how much variation would exist in the
system if there were no transmission constraints or losses. The hypothetical transmission situations
named sub-region and BA each indicate how much variation would exist in the system if each sub-region
and balancing area, respectively, were responsible to follow their own load and integrate their own
variable resources. Figure 5.11 shows the HVD plots for the LNWS SHAPE for the three hypothetical
transmission situations.

               Figure 5.11, Hourly Variation Duration Plots for Hypothetical
                         Transmission Situations – 2029 Profiles




As the transmission system is developed and as exchange transactions occur, the net amount of
variation in the system tends to decrease. This is no surprise since a more developed transmission
system is able to take advantage of the diversity in the load and variable generation patterns over a
larger geographical area (i.e. an increase in variable generation or load at one location can be netted out
by a corresponding decrease in variable generation or load at another location). The HVD curves
assume a fully cooperative dispatch, in which all possible diversity is captured in trade among parties.

Figure 5.12 adds the HVD plot for the load shapes to the plots of the LNWS shapes for the three
hypothetical transmission situations postulated above.




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                              2029 TEPPC Studies Results Report



               Figure 5.12, Hourly Variation Duration Plots Load and LNWS
                                 Shapes for 2029 Profiles




As the transmission system is capacity rises, the hourly MW variation in the LNWS shapes approaches
the hourly MW variation in the load shapes. Also, if there is sufficient transmission to deliver power
between any two nodes in the WECC then the hourly MW variation in the load shapes is approximately
the same as the hourly MW variation in the LNWS shapes. The increase in MW variation of the LNWS
shapes when compared to the MW variation of the load shapes is given in Table 5.3 below.

                    Table 5.3, Increase in MW Variation of LNWS Shapes
                        Compared to MW Variation of Load Shapes
                                   LNWS Shape        Percent Increase
                                      WECC                -1.5%
                                    Sub-Region            20.0%
                                        BA                35.5%

Comparing the Hourly Variation of the load shapes with the LNWS shapes in MWs can be deceiving
because the magnitude of the LNWS shapes is less than the magnitude of the load shapes. As a result, a
MW change in a LNWS shape tends to constitute a greater percentage change in magnitude than the
same MW change in a load shape. In other words, since variable generation displaces dispatchable
generation, there are fewer committed dispatchable generators that can follow load and integrate
variable generation during any given hour (i.e. each committed dispatchable generator needs to move
more to integrate the same MW change in the system). One way to account for this in a HVD plot is to
display the hourly variation as a percent change in magnitude instead of MWs as in Figure 5.13 below.




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                              2029 TEPPC Studies Results Report


           Figure 5.13, Hourly Variation Duration Plot as a Percent of Change




When the displacement of flexible capacity is accounted for, there is quite a bit more variation in the
2029 LNWS shapes then there is in the 2029 load shapes even if an ideal transmission system is
assumed. This suggests that transmission expansion alone is not enough to integrate high penetrations
of variable resources. Other forms of integration must be used in conjunction with transmission
expansion when building future resource scenarios with high penetrations of variable resources. The
key points of this discussion are:
     As the transmission system is built out, the net amount of variation in the system tends to
        decrease by taking advantage of the diversity in the load and variable generation shapes
     The addition of variable generation tends to increase the amount of variation in the system,
        while displacing generation that is able to mitigate the variation in the system (i.e. when
        variable generation is added the variation in the system increases and the system’s ability to
        deal with the variation decreases simultaneously).
     Other forms of integration must be used in conjunction with transmission expansion when
        building resource scenarios with high penetrations of variable resources.



6. Comparison of TEPPC 2029 Cases with WWSIS Report

                       To be written after completion of discussions
                                with NREL and GE Energy.




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2029 TEPPC Studies Results Report




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