GHG Emissions Reporting in the California Independent System Operator (CAISO) Energy Imbalance Market (EIM)

On Monday, the CAISO hosted a call to review the Draft GHG Emission Tracking Report and methodology paper that explains the draft’s preliminary results.  The report shows estimated GHG emissions for dispatch of internal CAISO resources, net imports (including dynamic resources that are an interchange schedule energy transfer between the CAISO and an outside balancing authority area (BAA) or EIM BAA and another BAA if in the real-time market), and transfers from western EIM entities into the CAISO BAA.  This post will discuss these documents to frame the value and limits of this type of reporting by the CAISO.

The value of this information stems primarily from greater transparency into the effect of the EIM market on GHG emissions to serve CAISO load in the wholesale real-time market.  This report and methodology is not intended or designed to resolve issues previously identified in the EPIC Energy Blog around GHG emission causation, unspecified power, or the CAISO’s regional integration of GHG compliance document regarding the forward, day-ahead market.  In light of this, the use of a counter-factual method (explained below) does appear to provide better transparency on the effect of the EIM because the counter-factual method input uses actual up or down dispatch orders to generators that were used to balance the system, which appears to eliminate unspecified power imports for the margin of electricity imported by the EIM to the CAISO.  The underlying assumptions for a GHG emission counter-factual methodology uses the same counter-factual method as the EIM Benefit Report Methodology that provides limited actionable information for cap-and-trade attribution evaluation or GHG emission accounting. Said another way, this report is independent of the California Air Resources Board’s Cap-and-Trade program and its current action to quantify GHG emissions from the EIM and any secondary dispatches as well as all local GHG emission accounting causation efforts.

The report states the following method to calculate overall GHG emissions to serve CAISO load:

GHG emissions from internal ISO dispatches including dynamic schedules (+) GHG emissions from net imports (+) GHG impacts from EIM transfer into the CAISO using a counter-factual determination (-) GHG impact from EIM transfers out of the CAISO using a counter-factual determination.

This method uses the following assumptions.  The CAISO explains that GHG emissions from internal CAISO dispatches includes all resources dispatched within the BAA to serve CAISO load (including dynamic resources).  GHG emissions from net imports include the net of all the energy to be transferred to or from the CAISO BAA from or to another BAA (e.g., Pacific Corp West) based upon agreed-upon megawatts, start and end time, beginning and ending ramp times and rate, and type required from delivery and receipt of power and energy between the source and sink BAA involved in the transaction. Net imports are therefore imports that serve CAISO load and excludes EIM transfer into or out of the CAISO.

GHG emissions from EIM transfers in and out of the CAISO use a counter-factual determination that quantifies GHG emission displacement of emitting resources. This is based on the idea that EIM transfers into the CAISO serve load that would have otherwise been served by other resources within the CAISO or imported to the CAISO.  EIM transfers out of the CAISO serve load in the EIM balancing area that would have otherwise been served by other resources within in the EIM balancing area or imported into the EIM balancing area.  The counter-factual dispatch method uses the same amount of real-time load imbalance in each BAA area without EIM transfers with neighboring EIM BAA areas.  EIM transfers are unidirectional for each 5-minute interval.

Finally, the heat rate used to calculate GHG for a resources is a specific heat-rate provided by the resources scheduling coordinator.  However, the CAISO uses CARB’s default unspecified GHG emission factor of 0.0428 mTCO2/MMTBU for net imports in the CAISO and EIM that lack a specified emission factor.  Emission factors are calculated, with standard unit conversions as:

GHG emissions (mTOC2) = resource heat rate (MMBTU/MWh) * CO2 emission factor by resource type (mTCO2/MMBTU) * Energy (MWh).

From this methodology, the CAISO calculated total GHG emission to serve CAISO load with the caveat that GHG impacts from EIM transfers using the counter-factual dispatch began in January 2016 and, prior, “GHG resource allocation in each EIM entity was used for EIM transfers.”  This makes it difficult to compare 2014 and 2015 to 2016 as a different GHG emission method was used.  Nonetheless, the results of CAISO calculations are presented in the table below.


The CAISO further broke down the EIM GHG reductions based on the counter-factual dispatch methodology from the CAISO’s EIM quarterly benefits reports to September 2016. The results are presented below.


The chart broadly illustrates that the cumulative GHG reduction peaks in early Summer, presumably because renewable energy is optimized across the EIM, and decreases in the late Summer as California load increases creating a sink for renewable energy that increases emissions from emitting resources in the EIM BAA areas.  More time is needed to fully understand these trends and the methodology.  As the EIM continues to perform, more data about EIM operation during specific times, days, and months will allow for comparison and analysis.  We will continue to report on GHG emission methodology in the EIM and potential expanded CAISO regional market.



About Joe Kaatz

Staff Attorney at the Energy Policy Initiatives Center, University of San Diego School of Law.
This entry was posted in Energy, Greenhouse Gas, Renewable Energy and tagged , , , , , , , , . Bookmark the permalink.

One Response to GHG Emissions Reporting in the California Independent System Operator (CAISO) Energy Imbalance Market (EIM)

  1. Pingback: AB 79: Quantifying Hourly GHG Emissions from Unspecified Electric Generation Sources | The EPIC Energy Blog

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