20240213PAC to Staff 25-37.pdf

1407 W North Temple, Suite 330 Salt Lake City, Utah 84116
February 13, 2024 Monica Barrios-Sanchez Commission Secretary
Idaho Public Utilities Commission 11331 W. Chinden Blvd. Bldg. 8, Ste. 201-A Boise, ID 83714
[e-mail]
[e-mail] RE: ID PAC-E-23-24 IPUC Set 2 (25-37)
Please find enclosed Rocky Mountain Power’s Responses to IPUC 2nd Set Data Requests 25-37.
Provided via BOX are Confidential Attachments IPUC Audit 26-1, 26-2, and 27. Confidential information is provided subject to protection under IDAPA 31.01.01.067 and 31.01.01.233, the Idaho Public Utilities Commission’s Rules of Procedure No. 67 – Information Exempt from
Public Review, and further subject to the non-disclosure agreement (NDA) executed in this
proceeding. If you have any questions, please feel free to call me at [phone]. Sincerely,

____/s/____ J. Ted Weston
Manager, Regulation
Enclosures
RECEIVED
Tuesday, February 13, 2024 12:11:51 PM
IDAHO PUBLIC
UTILITIES COMMISSION
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 25
IPUC Data Request 25 The 2017 Flexible Reserve Study (FRS) considered inter-hour system balancing integration costs. Please respond to the following:

(a) Please define inter-hour system balancing and explain how inter-hour system balancing can help integrate wind and solar.
(b) Please explain why the 2017 FRS considered inter-hour system balancing
integration costs and why the FRS in this case did not consider inter-hour system balancing integration costs. Response to IPUC Data Request 25
(a) PacifiCorp’s 2023 Flexible Reserve Study (FRS) accounts for intra-hour
uncertainty, changes within an hour relative to a forecast leading up to that hour. Inter-hour system balancing in PacifiCorp’s 2017 FRS accounted for day-ahead system balancing costs borne from committing generation
resources against a forecast of load and wind generation and then dispatching
generation resources under actual load and wind conditions as they occur in real-time. The optimized commitment of gas plants based on the day-ahead forecast of load and variable energy resources (VER) may not be the optimized commitment relative to the actual load and variable energy resources. For example, if load is expected to be high the next day, it may be
economic to start up an additional gas plant. If actual load does not reach the
expected level, the gas plant may not be needed. The inter-hour system balancing integration cost reflects the additional cost of starting and operating the plant, possibly at minimum, relative the lower cost resources that could
otherwise have been used to serve that load. The same thing is true for wind,
if wind capacity is projected to be high for the next day, a combined cycle gas plant may be economic to leave offline. However, if the actual wind generation comes in lower, higher cost market purchases or higher heat rate quick start gas plants may need to be used instead. Because PacifiCorp’s integrated resource plan (IRP) modeling is based on a fixed, i.e. known, load,
wind, and solar profiles, it does not capture this day-ahead uncertainty.
(b) In PacifiCorp’s 2019 FRS, PacifiCorp dropped the inter-hour system balancing integration cost. The cost was minimal in the 2017 FRS, and the Company’s modeling did not capture flexibility in energy imbalance market (EIM) to use excess committed resources to meet regional demand when needs are lower than predicted on a day-ahead basis or to take advantage of lower cost regional supply, when needs are higher than predicted on a day-ahead basis. The flexibility in EIM would be expected to reduce the inter-hour balancing cost further. While day-ahead costs are likely significant for the
portfolio as a whole, they do not change much with incremental wind and
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 25
solar additions and are likely to drop further when PacifiCorp joins a day-ahead market, such as the California Independent System Operator’s (CAISO) extended day-ahead market (EDAM), which is expected in the next few years.
PacifiCorp’s 2023 IRP, 2019 IRP and 2017 IRP are publicly available and can be
accessed by utilizing the following website link: Integrated Resource Plan (pacificorp.com)

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 26
IPUC Data Request 26 The proposed integration charges are determined based on the preferred portfolio from the 2023 Integrated Resource Plan (IRP). Please respond to the following
questions:
(a) Please list contract changes that have occurred since the development of the preferred portfolio, which include but are not limited to newly approved
contracts, terminated contracts, signed contracts if pre-approval from the
Commission is not needed. (b) If contract changes are added to the preferred portfolio, please explain the impact to the amount of regulation needed and provide the updated integration charges with work papers calculating the new charges.

(c) Please explain if the contract changes will trigger replacement or addition of resources that are already in the preferred portfolio. If so, please describe how the replacement or addition is implemented and provide examples to illustrate
the process.
(d) Please explain how the timing of the replacement or addition is determined. Response to IPUC Data Request 26
(a) Please refer to Confidential Attachment IPUC 26-1 which provides details on
contract changes relative to PacifiCorp’s 2023 Integrated Resource Plan (IRP) preferred portfolio, and which provides the updated portfolio information provided in the Company’s filing requesting an update to the capacity
deficiency date for qualifying facilities (Case PAC-E-24-01). Note: this file
contains the capacity contribution of resources, not nameplate. Please refer to Confidential Attachment IPUC 26-2 which identifies the associated changes in solar resources. No changes in wind resources have been identified at this time.
(b) The Company does not expect regulation reserve requirements to change
significantly as a result of modest changes in the portfolio and has not prepared the requested calculations. (c) The Company has not yet determined how contract changes will impact the preferred portfolio. The Company’s 2023 IRP Update is expected to be published on April 1, 2024 and will incorporate both contract changes and other updated assumptions, as described in the draft 2023 IRP Update released on January 31, 2024. PacifiCorp’s draft 2023 IRP Update is publicly available and can be accessed by utilizing the following website link:
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 26
https://www.pacificorp.com/content/dam/pcorp/documents/en/pacificorp/energy/integrated-resource-plan/2023_IRP_Update_Draft.pdf (d) The Company’s PLEXOS model develops portfolios based on the relative
economics of a variety of resource options across the IRP study horizon, as
discussed in Volume I, Chapter 8 (Modeling and Portfolio Evaluation) in PacifiCorp’s 2023 IRP, available online at:
PacifiCorp’s 2023 IRP is publicly available and can be accessed by utilizing the
following website link: Integrated Resource Plan (pacificorp.com) Confidential information is provided subject to protection under IDAPA
31.01.01.067 and 31.01.01.233, the Idaho Public Utilities Commission’s Rules of
Procedure No. 67 – Information Exempt from Public Review, and further subject to the non-disclosure agreement (NDA) executed in this proceeding.

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 27
IPUC Data Request 27 Page 6 of the Application states “the Company respectfully requests that the wind integration rate be decreased from $1.25 to $1.18 per MWh, in 2024 dollars, and
the solar integration rate increased from $0.96 to $1.40 per MWh, in 2024
dollars” Please explain why the wind integration rate decreases while the solar integration rate increases.
Response to IPUC Data Request 27
Referencing the Company’s Application in this proceeding dated November 29, 2023, the Company responds as follows: The integration rates are based on three main factors:

- Hourly reserve requirements - Hourly reserve costs - Annual resource capacity factor

These factors determine the integration rate as follows: Integration = ∑ Hourly reserve requirements * Hourly reserve costs Annual capacity factor
The total reserve requirements for wind are generally somewhat higher than for
solar, however, this is outweighed by a lower cost of reserves in the hours when reserves need to be held for wind, relative to the hours in which they are needed for solar. In addition, annual capacity factors (CF) for wind tend to be higher than
higher than for solar, resulting in a lower cost per megawatt-hour ($/MWh),
though the overall integration cost paid for a wind qualifying facility might be larger than for a solar qualifying facility with the same nameplate. Solar output is highest in the summer, and market prices and operating costs are generally higher in the summer, particularly in the late afternoon as solar is
ramping off. Reserve requirements are also somewhat higher for solar in the
summer, relative to the winter. In contrast, wind reserve requirements are relatively flat across the year, though slightly lower in July and August when reserve costs are highest.
Please refer to Confidential Attachment IPUC 27 which provides details on the statistics described above. Differences relative to the integration rates previously in effect reflect a number of changes since the prior analysis. Since PacifiCorp’s 2019 Integrated Resource
Plan (IRP), the flexible reserve study (FRS) methodology has incorporated more
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 27
actual solar operational data that was not previously available. Hourly reserve costs have also changed as a result of the evolution of PacifiCorp’s resource mix, as well as based on changes in electricity and gas prices that impact the economics of the Company’s fleet of resources.

Confidential information is provided subject to protection under IDAPA 31.01.01.067 and 31.01.01.233, the Idaho Public Utilities Commission’s Rules of Procedure No. 67 – Information Exempt from Public Review, and further subject
to the non-disclosure agreement (NDA) executed in this proceeding.
Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 28
IPUC Data Request 28 Please explain why the wind integration changes filed in this case are different than the wind integration charges filed in the 2023 IRP contained in the Excel file
“Fig Fl l 23IRP Wind Solar Integration.xlsx” in Case No. PAC-E-23-10.

Response to IPUC Data Request 28 Between PacifiCorp’s draft 2023 Integrated Resource Plan (IRP) dated March 31, 2023 and PacifiCorp’s published / final 2023 IRP dated May 31, 2023, changes in the final scenario modeling resulted in different hourly reserve costs, and thus
different integration costs. The wind integration charges filed in this proceeding, Case PAC-E-23-24, are consistent with the published / final 2023 IRP dated May 31, 2023. The associated
files are publicly available and can be accessed by utilizing the following website link: https://www.pacificorp.com/content/dam/pcorp/documents/en/pacificorp/energy/integrated-resource-plan/2023-irp/2023-irp-support-studies/2023_IRP_May_31_Data_Disk_Public.zip
Please refer to the file: \Chapters & Inputs\Appendix F - Flexible Reserve Study\(P)-Fig F11 23IRP Wind Solar Integration.xlsx
The referenced values from Case PAC-E-23-10 (PacifiCorp – Application for Approval of 2023 Integrated Resource Plan (IRP)) are from the Company’s draft 2023 IRP filing dated March 31, 2023. The values are also publicly available and can be accessed by utilizing the following website link:
https://www.pacificorp.com/content/dam/pcorp/documents/en/pacificorp/energy/i
ntegrated-resource-plan/2023-irp/2023-irp-support-studies/2023%20IRP%20Data%20Disc%20(Public).zip
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 28
Please refer to the file: “\Chapters, Appendices, and Input Assumptions\Chapters and Appendix\Appendix F - Flexible Reserve Study\Fig F11 23IRP Wind Solar Integration.xlsx”.

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 29
IPUC Data Request 29 Please explain why the solar integration charges filed in this case are different than the solar integration charges filed in the 2023 IRP contained in the Excel file
“Fig Fl I 23IRP Wind Solar Integration.xlsx” in Case No. PAC-E-23-10.

Response to IPUC Data Request 29 Please refer to the Company’s response to IPUC Data Request 28.
Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 30
IPUC Data Request 30 Page 152 of the FRS in Attachment 1 of the Application states "[t]o estimate wind and solar integration costs for the 2023 IRP, PacifiCorp prepared a PLEXOS
scenario that reflected the final regulation reserve requirements, consistent with
the Company's exiting wind and resources plus selections in the preferred portfolio." Please respond to the following:
(a) Please explain if the selected resources in the preferred portfolio include solar
and solar paired with storage. (b) Please explain whether solar and the solar component in the solar paired with storage are treated in the same way in the FRS. If not, please explain the difference.

(c) Please explain if the selected resources in the preferred portfolio include wind and wind paired with storage.
(d) Please explain whether wind and wind component in the wind paired with
storage are treated in the same way in the FRS. If not, please explain the difference. Response to IPUC Data Request 30 Referencing PacifiCorp’s 2023 Integrated Resource Plan (IRP), Volume II, Chapter F (Flexible Reserve Study), the Company responds as follows:

(a) All solar resources are included in the regulation reserve calculation, even if they are paired with storage. (b) All solar resources are treated the same way in the flexible reserve study (FRS), whether they are paired with storage or not. (c) All wind resources are included in the regulation reserve calculation, even if they are paired with storage.
(d) All wind resources are treated the same way in the FRS, whether they are paired with storage or not. Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 31
IPUC Data Request 31 Please respond to the following regarding Tab "23 IRP Summary" of the work paper "20231129Workpapers.xlsx" included in the filing.

(a) Column H and I show the values of Flat Reserves. Please define Flat Reserves.
(b) Please explain how values in column H and I are determined and provide
workpapers that calculate those values with formula intact. (c) Cell L9 shows a wind integration charge of $1.20/MWh in 2022 dollars. Please explain how the value is determined and provide work papers that calculate the value with formula intact.

(d) Cell M9 shows a wind integration charge of $1.48/MWh in 2022 dollars. Please explain how the value is determined and provide work papers that calculate the value with formula intact.
Response to IPUC Data Request 31 The Company assumes that work paper “"20231129Workpapers.xlsx" is intended to be a reference to the Microsoft Excel work paper supporting the Company’s Application in this proceeding, specifically file “Workpaper - ID AC 23IRP Wind Solar Integration”. Based on the foregoing assumption, the Company responds as follows:

(a) “Flat Reserves” means the simple average price for reserves, i.e. with an equal weighting for all hours in the month. The price is also distinguished between the PacifiCorp East (PACE) balancing authority area (BAA) and the PacifiCorp West (PACW) BAA which have separate reserve requirements and reserve supplies, though transfers between these areas are allowed up to certain limits. (b) Please refer to the Company’s response to IPUC Data Request 14, specifically Confidential Attachment IPUC 14-1, confidential file “CONF_App F 23IRP
Integration Cost ST19562.xlsb”, tab “Annual”, columns P and Q. (c) The value in cell L9 reflects the net present value (NPV) of the 2023 Flexible Reserve Study (FRS) results for wind integration over the period 2025 through 2042, adjusted for inflation back to 2022 dollars (2022$) for comparability with the 2021 FRS. The values shown in column E link to confidential file “CONF_App F 23IRP Integration Cost ST19562.xlsb” which was provided in Confidential Attachment IPUC 14-1. Please refer to the Company’s response to IPUC Data Request 27 which provides discussion of
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 31
the calculations within this file. (d) Please refer to the Company’s response to subpart (c) above. The same calculations are made, but for solar integration.

Recordholder: Dan MacNeil
Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 32
IPUC Data Request 32 Please respond to the following regarding the graph contained on tab "23 IRP Summary" of the work paper "20231129Workpapers.xlsx" included in the filing
(shown below):

(a) Please explain why wind integration charges decrease from 2025 through 2028.

(b) Please explain why solar integration charges increase from 2025 through 2026 but decrease from 2026 through 2028.
(c) Please explain why wind and solar integration changes show similar patterns
from 2028 through 2042. Response to IPUC Data Request 32 The Company assumes that work paper “"20231129Workpapers.xlsx" is intended to be a reference to the Microsoft Excel work paper supporting the Company’s Application in this proceeding, specifically file “Workpaper - ID AC 23IRP Wind
Solar Integration”. Based on the foregoing assumption, the Company responds as
follows: Please refer to the Company’s response to IPUC Data Request 27 which provides a discussion of the drivers of integration charges. In addition, please refer to the
Company’s responses to subparts (a) through (c) below: (a) Specific to wind integration in 2025 through 2028, PacifiCorp’s 2023 Integrated Resource Plan (IRP) preferred portfolio includes 954 megawatts (MW) of battery additions in 2025, 2,929 MW of battery additions in 2026
and more battery additions each year in 2027 through 2029. Battery resources
provide reserves over their entire operating range (i.e. with no minimum operating level), and can provide additional reserves while charging, as it can
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 32
be interrupted. This additional supply of reserve capable resources reduces the cost of reserves. While significant wind resources are added in 2025, additions in 2026 through 2028 are relatively low, therefore, they are unlikely to have a significant impact on reserve requirements or integration costs.

(b) Specific to solar integration, PacifiCorp’s 2023 IRP preferred portfolio has over 2,500 MW of solar resource additions in 2026. This results in higher reserve requirements, both as a result of the higher volume of solar, as well as
a result of lower diversity in the PacifiCorp East (PACE) balancing authority
area (BAA), as indicated in Table F.7 (PacifiCorp East Diversity by Portfolio Composition) in the 2023 Flexible Reserve Study (FRS). While solar additions continue each year through 2029, this is outweighed by the reduction in reserve costs driven by increasing battery supply.
(c) Once battery capacity in the portfolio is sufficiently large, most hours in the
year have no incremental cost for holding regulation reserves, as the otherwise available reserve supply in the absence of any changes to dispatch exceeds requirements in most hours. After 2038, retirements of thermal resources
result in a slight uptick of hours with a non-zero reserve cost, but it is still a
small fraction of the year. Because both wind and solar capacity are quite large by this point in the study, these changes in reserve supply costs are the primary driver across this timeframe, for both wind integration and solar integration.

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 33
IPUC Data Request 33 Please respond to the following regarding Figure F.3 through Figure F.10 in the FRS in Attachment 1 of the Application.

(a) Please explain what the solid lines in Figures F.3 through F.10 represent and how they are determined.
(b) Please explain why Figure F.3 through Figure F.8 display non-linear functions
with error as a percentage of capacity first increasing and then decreasing as the capacity increases. (c) Please explain why Figure F.9 and Figure F.10 display linear functions with error as a percentage of peak load constantly increasing as the peak load
increases.
(d) Please explain how "percentage of capacity" is determined in Figure F.3 through Figure F.8 and how the 2018 and 2019 data is used in determining the
"percentage of capacity".
(e) Please explain how "percentage of peak load" is determined in Figure F.9 and Figure F.10 and how the 2018 and 2019 data is used in determining the "percentage of peak load."
Response to IPUC Data Request 33
Referencing PacifiCorp’s 2023 Integrated Resource Plan (IRP), Volume II, Chapter F (Flexible Reserve Study), the Company responds as follows:

(a) The solid lines in the Flexible Reserve Study (FRS) figures are the quantile regression values for each class of reserve requirements. Ordinary regression values estimate the mean, i.e. 50th percentile from a set of response variables and predictor variables. Quantile regression estimates other specified percentile values. In this instance, the quantile regression reflects a very high
percentile, around 99 percent, because the applicable North American Electric
Reliability Corporation (NERC) standard only allows resource shortfalls or increases in load to exceed the available reserve supply by a small amount, and in a few hours.
(b) Generating resources generally cannot experience errors that exceed their forecasted level. If wind is forecasted at 50 megawatts (MW) out of 100 MW, but actually generates at zero, then the shortfall is 50 MW. While a small amount of station service (negative generation) can occur, this lower limit bounds the possible error. At low forecasted capacity factors (CF), actual
results do come in a zero fairly often, and there is a relatively linear and 1:1
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 33
relationship between the forecast and the possible error. However, as forecasted CFs increase, it becomes less and less likely that the actual output will go all the way to zero, so the quantile regression bends down to a more horizontal level, with small increases in possible error as forecasted output
continues to increase. Once wind speed or insolation reaches a certain point,
generation is maximized, and is generally limited by the capacity of the wind turbine, solar inverters, or the resource’s interconnection. At that point, higher wind speed or more sunlight will not result in more output. If wind speed or
insolation exceeds that level, modest shortfalls in wind speed or insolation are
not sufficient to reduce unit output and generation, which does not result in a deviation as presented in the FRS figures. As a result, forecasting is more accurate at high CFs, and errors are reduced, allowing for reserve requirements to fall somewhat when forecasts are at the upper end of possible output.

(c) Please refer to the Company’s response to IPUC Data Request 23, specifically subpart (e).
(d) Percentage of capacity in Figure F.3 through Figure F.8 of the FRS is
calculated as the hourly forecasted generation, divided by the hourly installed capacity (generally the interconnection limit, which is often the same as the nameplate capacity). Both forecasted generation and installed capacity reflect data during the historical period.
(e) Percentage of peak load in Figure F.9 and Figure F.10 of the FRS is calculated
as the hourly forecasted load, divided by the highest hourly load for any hour in that year. Both forecasted and actual load reflect data during the historical period.

PacifiCorp’s 2023 IRP is publicly available and can be accessed by utilizing the following website link: Integrated Resource Plan (pacificorp.com)

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 34
IPUC Data Request 34 Please explain why the greatest diversity benefits are located in the bottom left area of Table F.7 on Page 150 of the FRS in Attachment 1 of the Application.
Also, please explain why the greatest diversity benefits are located in the bottom
right area of Table F.8 on Page 151 of the FRS. Response to IPUC Data Request 34

Referencing PacifiCorp’s 2023 Integrated Resource Plan (IRP), Volume II, Chapter F (Flexible Reserve Study), the Company responds as follows: The greatest diversity benefits occur when the reserve requirements for load, wind, and solar are relatively balanced, that is the available reserves are large
enough to cover a large deviation in load, wind, or solar. For example, if solar
capacity is relatively low, the reserves needed to cover load or wind will be well in excess of the amount needed for solar, and the reserves held will generally be needed regardless of the amount of solar up to a certain level. If solar capacity is
relatively high such that reserve requirements are in excess of the amount needed
for wind and load, the amount of wind and load has little impact on the reserve requirements, i.e. more of those could be added without additional reserve needs. In practice, the combined deviations of wind, solar, and load are somewhat additive, and the diversity varies across the day and throughout the year, so the most diverse combination is not a single point but rather a weighting of a variety
of conditions.
Specific to Table F.7 (PacifiCorp East Diversity by Portfolio Composition) of the FRS, there is already a substantial quantity of both wind and solar in the
PacifiCorp East (PACE) balancing authority area (BAA), therefore, the
requirements for load, wind, and solar are relatively balanced already. Additions of either wind or solar make the overall requirements less diverse, and while increases of both wind and solar in combination are better than either on their own, the requirements exceed what would otherwise be required for load and lead to relatively lower levels of diversity.

Specific to Table F.8 (PacifiCorp West Diversity by Portfolio Composition), there is relatively little solar capacity in the PacifiCorp West (PACW) BAA, therefore, increases in solar capacity make better use of existing reserve obligations for load and wind. Modest increases in wind and solar in combination can also make better use of existing obligations for load, but only up to a point, beyond which diversity falls again, as requirements exceed what would otherwise be required for load. PacifiCorp’s 2023 IRP is publicly available and can be accessed by utilizing the following website link:
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 34
Integrated Resource Plan (pacificorp.com)
Recordholder: Dan MacNeil
Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 35
IPUC Data Request 35 Please respond to the following regarding Tab "Table F.7-F.8" of the work paper "Fig Fl-2, Tab Fl-F8 App F - References Tables and Figures_2023 03 27.xlsx"
from Case No. PAC-E-23-10.
(a) Please define "Study Count" and explain what the values in column A represent.

(b) Please explain what the codes and the numbers in column B represent. (c) Please explain what the red area represents. (d) Please explain what the yellow area represents.

(e) Please explain why the regulation reserve amounts for Non-VER in column K and column Q are constant.
(f) Please explain why the regulation reserves amounts for load in column L and
column R are constant. (g) Please explain why the regulation reserve amounts for wind in column M and column S are not constant.
(h) Please explain why the regulation reserve amounts for solar in column N and
column T are not constant. (i) Please explain how the values in column E and column F are determined and
provide work papers that calculate these values with formula intact.
(j) Please explain how LOLP is used to determine the two heat maps on the tab. Response to IPUC Data Request 35
Referencing the public / non-confidential work papers supporting PacifiCorp’s
2023 Flexible Reserve Study (FRS) in the 2023 Integrated Resource Plan (IRP), specifically file “(P)-Fig F1-2, Tab F1-F8 App F - References Tables and Figures-2023 03 27”, the Company responds as follows: (a) Each “Study” is a different of wind and solar capacity. The count in column A identifies how many studies were performed. (b) Column B provides additional description of the study, specifically:
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 35
i. “Actual”: the 2018-2019 historical period. The prefix “A” indicates the study had wind and/or solar at 50-100 percent of the historical level. ii. “2021”: this study has wind and solar capacity based on executed
contracts in calendar year 2021. The studies that follow (a number in
column B with no prefix) include wind and solar combinations at or above the levels from 2021.
iii. “X”: this prefix indicates additional studies added to extend the range of
values to even greater levels of wind and/or solar than were previously identified, to accommodate larger selections of these resources in the portfolio. (c) The red highlight in columns C and D have no specific meaning.22 diversity
studies originally prepared included the “Actual” study, the “2021” study, and
the 20 numbered studies in column B based on the 2021 wind and solar capacities as described in the Company’s response to subpart (b) above. Studies extending below the “Actual” study capacity amounts and to excess
levels beyond the original set were added later.
(d) The yellow highlight in row 9 indicates formulas tied to stand-alone requirements from the 2018-2019 historical period. The remaining values in these columns are calculations based on row 9, pro-rating the stand-alone requirements relative to the change in wind and solar capacity in that study.

(e) For the purposes of calculating diversity as a function of the portfolio composition, non-variable energy resources (VER) were held constant. Many of these resources belong to third-party transmission customers, and are not
used to serve retail customers, therefore, the Company does not forecast
whether they will change over time. IRP modeling also generally has flat forecasted generation within a month for non-VERs in its own portfolio, this is in contrast with the 8,760 hour profiles used for wind and solar. As a result, it is not possible to forecast non-VER requirements specific to the IRP portfolio.

(f) For the purposes of calculating diversity as a function of the portfolio composition, load was held constant. The ultimate reserve requirement calculation accounts for changes in load through time, but the impact is modest. Adding a third dimension to Figure F.7 (Non-VER Regulation Reserve Requirements by Capacity Factor – PACE) and Figure F.8 (Non-VER Regulation Reserve Requirements by Capacity Factor – PACW) would have exponentially increased the number of studies required. (g) The stand-alone regulation reserve requirements for wind were assumed to be
proportionate with the amount of wind capacity in the portfolio. This is based
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 35
on the assumption that wind errors scale linearly with wind capacity. This is reasonable because the Company has relatively diverse wind and solar resources.
(h) Please refer to the Company’s response to subpart (e) above. Note: while
PacifiCorp West (PACW) solar resources had a relatively low total capacity in the historical period, all of the associated resources are under 10 megawatts (MW), therefore, the count is high. This results in diversity as their aggregate
output is not impacted by passing clouds to the same degree that a single 200
MW solar resource would be. (i) Please refer to the Company’s response to IPUC Data Request 6, and in particular Confidential Attachment IPUC 6-2.
(j) The forecasted reserve requirement must produce a loss of load probability
(LOLP) that is less than 0.25 hours per year for each balancing authority area (BAA), as discussed in the FRS. Because the targeted reliability level is relatively high, small changes in the reserves held can result in jumps in the
LOLP, so the identified values may be somewhat lower than the minimum
0.25 hour per year requirement. These columns just indicate that this level of reliability was achieved at the level of reserves identified in columns E and F, therefore, they do not directly impact the referenced tables. The diversity values in Table F.7 (PacifiCorp East Diversity by Portfolio Composition) and Table F.8 (PacifiCorp West Diversity by Portfolio Composition) reflect the
percentage reduction between the stand-alone requirements, including
grossed-up requirements consistent with the level of wind and solar, and the combined reserve requirement results in columns E and F.
PacifiCorp’s 2023 IRP is publicly available and can be accessed by utilizing the
following website link: Integrated Resource Plan (pacificorp.com)
Recordholder: Dan MacNeil
Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 36
IPUC Data Request 36 Please respond to the following regarding tab "Hourly" of the work paper "CONF _ App F 23IRP Integration Cost STI 9562.xlsx" from Case No. PAC-E-23-10.

(a) Please explain how the values in column N and column O are determined and provide work papers that calculate the values with formula intact.
(b) Please explain why some data in column N and column O are missing.
(c) Please explain why some data in column N and column O are negative. (d) Please explain how data in column D through column I are determined and provide work papers that calculate the values with formula intact.

(e) Please explain how the step of determining data in column D through column I fits into the context of calculating regulation reserves by summing stand-alone regulation reserves and then subtracting portfolio diversity benefits and EIM
benefits.
Response to IPUC Data Request 36 Referencing the confidential work papers supporting PacifiCorp’s 2023 Flexible Reserve Study (FRS) in the 2023 Integrated Resource Plan (IRP), specifically
confidential file “CONF_App F 23IRP Integration Cost ST19562”, the Company
responds as follows: (a) Please refer to the Company’s response to IPUC Data Request 14, specifically
Confidential Attachment IPUC 14-1, which provides the referenced calculations of
integration cost. The calculation in column N reflects the hourly regulation reserve requirement in PacifiCorp East (PACE) when 5 megawatts (MW) of additional wind is added to the preferred portfolio (column E) less the hourly regulation reserve requirement in
PACE in the preferred portfolio (column D), multiplied by the marginal cost of
regulation reserves in PACE from the preferred portfolio (column K), as reported by the PLEXOS model for the short-term study index 19562 plus the hourly regulation reserve requirement in PacifiCorp West (PACW) when 5 MW of additional wind is added to the preferred portfolio (column H) less the hourly regulation reserve requirement in PACW in the preferred portfolio (column G), multiplied by the marginal cost of regulation reserves in PACW from the preferred portfolio (column L), again from the PLEXOS model for study index “19562”. (b) The Company has not identified any missing values in columns N through O but
would note that where the value is zero it is formatted as a dash (“-“). Zero values
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 36
typically occur when the price of regulation reserve for an hour is zero, which can happen when supply is plentiful. (c) Reserve prices are never less than zero, because reserves do not have to be
provided, even if they are available, so this does not result in negative values.
When negative values occur it indicates that hourly reserve requirements are lower when additional wind or solar are added. Please refer to the Company’s response to IPUC Data Request 14, specifically Confidential Attachment IPUC 14-1, which
provides the specific calculations of the hourly reserve requirements. In general,
the diversity calculation reflects an annual total, but diversity actually changes from hour-to-hour. The regulation reserve forecasting technique merely attempts to keep the overall risk of shortfalls below specified levels. As the portfolio changes, covering increased risks in some hours may allow for reduced reserves in other hours. This is particularly true for solar, where the regulation reserve
requirement overnight when no solar generation exists may go up or down slightly
as a result of the overall diversity level even if additional solar generation during the day drives larger requirements during the day.
(d) Please refer to the Company’s response to subpart (a) which provides a description
of each of the columns of data. For the calculation of the data in columns D:I, please refer to the Company’s response to IPUC Data Request 14, specifically Confidential Attachment IPUC 14 -1. Specifically, column D in tab “Results” in the following files:
Column D: Regulation Reserve Requirement 23IRP - East Template 02132023 v2
CONF.xlsm. Column E: Regulation Reserve Requirement 23IRP - East Template 02132023 v2
w5W CONF.xlsm.
Column F: Regulation Reserve Requirement 23IRP - East Template 02132023 v2 w5S CONF.xlsm. Column G: Regulation Reserve Requirement 23IRP - West Template 02132023 v2
CONF.xlsm.
Column H: Regulation Reserve Requirement 23IRP - West Template 02132023 v2 w5W CONF.xlsm. Column I: Regulation Reserve Requirement 23IRP - West Template 02132023 v2 w5S CONF.xlsm. Within each of the referenced files, tab “BAA Reserve Requirements” calculates the hourly reserve requirements based on the hourly forecast of load, wind, and
solar generation, along with peak load, wind nameplate capacity, and solar nameplate capacity, as shown in columns G:Q. The ratio of load, wind and solar
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 36
capacity to the historical FRS analysis is calculated in columns R:T. These data points and the associated coefficients from the FRS are used to calculate the stand-alone reserve requirements for each class (load/wind/solar/non-variable energy resources) in columns U:X. The portfolio requirement, after accounting for
diversity, is calculated in column Z, while the requirement after accounting for
energy imbalance market (EIM) diversity and minimum flexible resource requirements is calculated in column AB. This tab calculates one year of reserve requirements at a time, and the year may be switched automatically by changing
cell M3 of tab “Summary”. A Microsoft Excel macro was used to populate tab
“Results” by calculating each year and pasting values from column AB on tab “BAA Reserve Requirements” onto column D in tab “Results”. (e) Please refer to the Company’s responses to subparts (a) and (d) above. The calculations reflected in columns D:F provide PACE regulation reserve
requirements for three slightly different portfolios:

• Column D: The preferred portfolio.
• Column E: The preferred portfolio with an additional 5 MW of wind.
• Column F: The preferred portfolio with an additional 5 MW of solar.

Stand-alone requirements are higher when more resources are added to the portfolio, rising in proportion with the capacity increase, however, the overall requirement generally goes up by a lower amount because of diversity. The specific level of diversity depends on what resource is being added on the composition of the portfolio (i.e. how much wind and solar are in the preferred
portfolio). The portfolio diversity benefits in the files referenced in the Company’s
response to subpart (d) above are shown in columns B:E in tab “Portfolio Diversity”. The values vary by hour and season and vary with changes in the portfolio though it is slight in the referenced data because a five megawatt change
in resources is small relative to the portfolio as a whole. EIM benefits on tab
“EIM Diversity” do not change with the portfolio in the way that the Portfolio Diversity does, but instead are scaled within the calculations in column AB on tab “BAA Reserve Requirements” based on the level of load, wind, and solar relative to the historical period.

Recordholder: Dan MacNeil Sponsor: Dan MacNeil
PAC-E-23-24 / Rocky Mountain Power February 13, 2024 IPUC Data Request 37
IPUC Data Request 37 Because the Company proposes non-levelized integration charges from 2024 through 2048, please update the work paper "CONF _App F 23IRP Integration
Cost ST19562.xlsx" from Case No. PAC-E-23-10 to reflect data through 2048.
Response to IPUC Data Request 37
Referencing the confidential work papers supporting PacifiCorp’s 2023 Flexible
Reserve Study (FRS) in the 2023 Integrated Resource Plan (IRP), specifically confidential file “CONF_App F 23IRP Integration Cost ST19562”, the Company responds as follows: The Company does not have any model data for periods after 2042 from Case No.
PAC-E-23-10, or otherwise, so it cannot update the integration charges calculated
in the referenced work paper. Given the general trends in the data, namely the relative stability of the integration costs leading up to 2042, the Company’s Application in this proceeding reflects 2042 integration costs escalated at inflation
for 2043-2048, as shown in the Company’s work paper supporting the Company’s
Application in this proceeding, specifically file “Workpaper - ID AC 23IRP Wind Solar Integration”, tab “ID Integration”. Recordholder: Dan MacNeil

Sponsor: Dan MacNeil