Mike Jaske, California Energy Commission

Allocating Additional Achievable Energy Efficiency Program Initiatives to Load Busses for Power flow Modeling

Mike Jaske, California Energy Commission

March 13, 2014

Purpose

This paper documents the preparation of power flow modeling inputs for additional achievable energy efficiency (AAEE) program initiatives for use in determining the impacts of such initiatives on local capacity area (LCA) requirements. This work was undertaken by the California Energy Commission with support from the California Public Utilities Commission (CPUC). These modeling inputs enable the California Independent System Operator (CA ISO) to determine how such program impacts would reduce and/or modify local capacity area (LCA) requirements. The approach allocates the impacts of these prospective programs to specific transmission system busses on the basis of data from the distribution utilities about coincident load at CA ISO summer peak conditions and the mix of load by customer type on each bus. The results of this analysis will be used by the CA ISO pursuant to the inter-agency agreement to develop and use consistent planning assumptions in each agency’s planning processes.[1]

This paper provides some background, a review of the data needed to implement the method used, a summary of the method, a comparison of the new results to the previous round of analyses, and some suggested next steps.

Background

Pursuant to its statutory requirements, the Energy Commission prepares and adopts a long-term demand forecast for each region of the state on a biennial basis as part of its Integrated Energy Policy Report (IEPR) proceedings. While such demands forecast include the impacts of considerable body of energy efficiency program impacts as well as some voluntary, price-induced energy efficiency, not all energy efficiency reasonably expected to occur is included. This primarily results from the uncertainties about future funding of utility-sponsored programs, the design of the programs, the degree of stringency of Energy Commission-adopted building standards, and comparable uncertainties about stringency of Energy Commission- and federally-adopted appliance efficiency standards. While the Energy Commission chooses to exclude such uncertain impacts from the baseline demand forecasts it adopts, the Energy Commission cooperates with the CPUC and other entities in attempting the quantify the impacts of additional energy efficiency policy initiatives and to determine the incremental impacts of such initiatives above and above those already included in its baseline demand forecasts.

In 2009 and 2010, the Energy Commission in conjunction with the CPUC and its contractor Itron, quantified the incremental savings for several alternative energy efficiency potential scenarios developed as part of the CPUC’s 2008 Energy Efficiency Strategic Plan. These were referred to at that time as incremental uncommitted (IncUnc) energy efficiency savings. In 2009, the Air Resources Board was directed by AB1318 (V. Manuel Perez, Chapter 285, Statutes of 2009) to develop a report assessing the air emission offsets associated with generating facility additions needed to satisfy reliability requirements in the South Coast Air Basin. The legislation also directed ARB to assess the degree to which such emission offset needs might be reduced through demand-side measures. The CA ISO, Energy Commission, CPUC and ARB collaborated to perform power flow modeling to determine the base resource additions needed to satisfy local capacity area requirements. To assess the degree to which local capacity area requirement might e reduced by demand-side measures, the CA ISO agreed to perform addition power flow assessments using load forecasts reduced by the allocation of incremental uncommitted (IncUnc) energy efficiency savings by load bus.

To translate from service area-wide aggregated projections to energy efficiency savings at load busses for the CA ISO’s use, Energy Commission developed a method that relies upon data from the IOUs about the load on each bus at the time of coincident ISO system peak and the composition of such load by customer type. The basic approach has been recognized by the CPUC in specification of assumptions for local capacity studies.[2] The ISO subsequently used these load bus-specific energy efficiency savings to conduct power flow modeling studies both for ARB’s AB1318 project as well as a study specific for the 2012 Long-Term Procurement Plan (LTPP), Track 4 rulemaking.[3] The ISO submitted the results of its local capacity area studies as testimony in the 2012 LTPP, Track 4 proceeding.[4]

The Energy Commission developed the present set of demand forecasts and additional achievable energy efficiency (AAEE) savings projections as part of its 2013 IEPR. The AAEE savings projections for this cycle of analysis were developed at the level of climate zone for PG&E and SCE service areas for which there are multiple climate zones. For the SDG&E service area, the Energy Commission continues to use a single climate zone so no further disaggregation was developed.

This paper documents the refinements in allocating AAEE savings projections from climate zone to load bus for use by the ISO in its 2014/15 Transmission Planning Process.

Critical Information Needed from CPUC-Jurisdictional Utilities

To implement the method chosen to allocate AAEE savings from climate zones to load busses required information from the IOUs about their systems. A data request was prepared that refined data originally obtained from the IOUs for the first cycle of this analysis.[5] The data request gathered information at the proper level of detail about the topology of the PTO system, for CA ISO system peak conditions, and about the mix of loads on each modeled load bus.In October 2013, the CPUC and Energy Commission staff developed a draft data request for each PTO/IOU. This data request was discussed with each of the IOUs, refined slightly, and issued in early November. Responses were requested by within six weeks. SCE and SDG&E submitted data in late December and PG&E submitted its data in early January 2014.

Transmission Modeling Conventions

Well established transmission modeling conventions govern the level of detail for each of the three participating transmission owner (PTO) that is modeled by the CA ISO for its transmission studies. For SCE and SDG&E, the convention adopted by the PTO and CA ISO is to aggregate load busses that are radial to the bulk power system. This is due to the fact transmission power flow assessments would be insensitive to the actual configuration of the sub-transmission and distribution system as long as the entire subsystem is radial to the bulk transmission system. This can result in load busses representing hundreds of megawatts of aggregate load even though individual substation busses carry smaller loads. In total SCE/CA ISO represents the SCE system with about 120 load busses. SDG&E/CA ISO represent the SDG&E system with about 110 load busses. In contrast, PG&E and the CA ISO have agreed to model the PG&E system at a much higher level of granularity. The PG&E system is represented by about 1400 load bus/circuit combinations with the load per bus rarely exceeding 50 MW. This is the level of detail for which AAEE savings must be allocated to be useful to the CA ISO in its transmission modeling studies.

Modeling Inputs Required by the ISO

While the CA ISO investigates transmission system impacts at various stereotypical types of system conditions, the focus for LCA requirements is 1:10 summer peak conditions. Due to the complexity of estimating sensitivity of specific measures to weather conditions the AAEE projections have only been developed for average summer peak conditions, and no specific adjustments are available to reflect 1:10 or 1:5 extreme conditions. AAEE savings projections exist for both annual energy and peak demand, but only power flow modeling of summer peak requires a disaggregation to load bus.

Customer Class Estimates of Peak Load

For all three IOUs, despite the deployment of interval metering systems to end-use customers, there is insufficient coverage of end-users to know the composition of load by customer class at system peak conditions for each bus.[6] Each utility provided slightly different methods using master file billing information on usage by customer and its rate tariff structure. IOUs applied these energy proportions to the measured bus loads to develop estimates of bus load by customer class. Further adjustments were made by the Energy Commission staff to match these customer class results with the disaggregation scheme for the AAEE savings projections.[7]

Zip Code of Load Busses

As noted earlier, the AAEE savings projections that need to be translated to load busses were developed at the climate zone level. To take advantage of this feature, the data request asked for the zip code in which the WECC load bus was physically located. Each IOU provided its locational information for the bus although it is understood that, especially for the SCE system with some very large aggregated busses, many additional zip codes would be encompassed by the end-user loads represented at that bus. Considerable difficulty was encountered in matching reported zip codes for some IOU load busses with publicly available information about substation locations. Some adjustments were made to reflect such public sources.[8]

Confidentiality

Each of the IOUs designated the responses to the data request (loads at 2012 CA ISO system peak and share by customer class on that bus) to be confidential. Accordingly, the CPUC transferred the data request responses to the Energy Commission pursuant to an existing confidentiality agreement in which the Energy Commission agrees to maintain data in a confidential manner and to not disclose the data in any aggregated way that could be “reverse engineered” back to the level that is confidential.

Additional Achievable Energy Efficiency Projections

There have been two previous versions of load bus savings prepared for use in various power flow modeling studies – principally for local capacity assessment purposes. These differ in the source of the additional achievable savings, in the data used for allocation from service area to load bus, which of several possible cases of incremental savings was allocated, etc. Table 1 provides an overview of the elements used in each of the three rounds of analysis (two previous versions and this current one).

Table 1: Overview of Incremental Savings Projections and Data for Allocation to Load Busses

Date of Release / Aggregate Savings Source / Vintage of Data for Allocating to Load Busses / Proceeding for Which Results Prepared (and Cases Assessed)
October 2011 / May 2010 IncUnc report (based on Itron/CEC assessment of 2008 Goals Study projections and 2009 IEPR load forecasts) / Summer 2009 or 2010 data obtained summer 2011 / ARB AB1318 studies (CEC/ARB-funded assessment by Navigant Consulting and ISO studies for ARB)
January 2013 / September 2012 IncUnc revision by CEC staff based on preliminary CPUC-funded potential and goals study and 2012 IEPR Update base forecast / Summer 2009 or 2010 data obtained summer 2011 / 2013/14 TPP used the low case IncUnc load bus projections
CPUC 2012 LTPP (D.12-12-010 and May 2013 ACR)
March 2014 / 2013 IEPR AAEE results by climate zone (December 2013), updated march 2014 to correct offsetting errors at the climate zone level / August 2012 data obtained late 2013 or early 2014 / 2014/15 TPP
Mid case AAEE for bulk system studies and LowMid case for local capacity area studies

2009 IEPR-Cycle Incremental Energy Efficiency Projections

As an element of the 2009 IEPR proceeding, the Energy Commission staff developed incremental energy efficiency impacts based upon the specific strategies that the CPUC had assessed as part of its 2008 Energy Efficiency Strategic Plan and in setting its goals for the three IOUs.[9] The strategies making up the scenarios involved various hypothetical energy efficiency programs, some extensions of existing programs extended further out into the future and some that were new. The focus of these programs was on residential and commercial building customer classes, not industrial or agricultural. The Energy Commission published its final estimates, along with recommendations for use in CPUC proceedings, in May 2010. The CPUC 2010 LTPP proceeding chose a specific scenario, with adjustments, that IOUs were required to use in the developing future resource plans for the common scenarios.[10]

2012 IEPR Update Incremental Savings Projections

For this effort, the Eneregy Commission used the preliminary potential and goals savings developed by the CPUC’s contractor (Navigant Consulting) rather than the 2008 vintage of goals adopted formally by the CPUC. These are savings, described in both annual energy and peak load reductions, for each IOU service area for each of the residential, commercial, industrial, and agricultural customer classes. For summer peak demand power flow modeling purposes, especially as the basis for 1:10 LCA requirements assessments, peak demand load reductions are the focus of interest. Allocation of these to PTO load busses used the same data and method as in the original analysis.

2013 IEPR AAEE Projections

As part of the 2013 IEPR proceeding, the Energy Commission staff developed projections of the incremental impacts of energy efficiency initiatives that are not included within the 2013 IEPR adopted baseline demand forecast. There are five AAEE saving cases that embody different categories of program initiative, different stringency of hypothetical standards updates, and in some case, the effect of technical developments through time. The results are documented in aEnergy Commission staff report.[11] These service area projections were also calculated at the climate zone level, which became the starting point for the allocation to load busses described in this paper. The newly obtained data for August 2012 load on busses at ISO system peak and the shares by customer type were used to allocate from aggregates at the climate zone level to individual load busses within that climate zone.[12]

Although the immediate need is for load reductions in years 2019 and 2024, the assessment was prepared for each year 2013 to 2024 should the intermediate values be of interest in other studies.

Method for Translating Service Area Impacts to Load Bus Impacts

To translate climate zone (PG&E and SCE) or service area (SDG&E) peak load reductions to individual bus peak load reductions, the following steps were implemented for each of three AAEE cases (mid, lowmid, and highmid):

1. Summarizeacross all program types within a customer sectorfrom the Energy CommissionAAEE spreadsheets within each climate zone (if any) to obtain annual peak load results for each customer sectorfor all years 2013 to 2024.

1. Obtain results of CPUC data request to each IOU (circa circa late 2013/early 2014) that identifies summer peak load by busbar by customer class, and for each load bus:

1. If necessary, multiply total busbar peak load by customer sector proportions to get absolute value of load at peak for each customer class;
2. Reconcile the split among customer classes with the disaggregation of AAEE by customer sector;
3. Review zip code assignments made by each PTO and adjust as needed;
4. Use zip code of each bus and merge climate zone identifier for that load bus; and
5. For each customer sector, tabulate results of step 2d to determine the proportion that each busbar is of all load busses in each climate zone for each customer sector, e.g. the results for each busbar is the value for each of the customer sectors that is its share of the climate zone at peak for that customer sector.

1. For each year 2013 to 2024, multiply the climate zone area peak load savings for each customer sector from step 1 by the customer type proportion of each busbar from step 2e.

1. Add up the six customer sectorimpacts at each busbar of step 3 to compute the total program impacts at each busbar.

1. Verify that the sum of impacts across all busbars matches the original climate zone peak load impacts of Step 1.

1. Save final busbar-specific program projections ina separate spreadsheet for forwarding to the CA ISO to avoid sending any information considered by the IOUs to be confidential.

This process was followed for each of the three PTO/IOU service areas, resulting in three spreadsheets that were forwarded to the CA ISO for use in modifying power flow base cases.

Comparing 2014 Results with Previous Ones

There are many ways to compare the results obtained using the new AAEE aggregate savings projections and new 2012 load bus data with the previous IncUnc aggregate savings projections allocated using the 2009/2010 load bus data.

The following comparisons will be discussed in detail below:

a.Aggregate comparison of the three AAEE cases with the corresponding three IncEE cases for peak laod savings. This provides an overall sense of the differences in load bus projections between aggregate AAEE/IncEE differences versus revisions due to allocation methodology.