Account for transmission losses / Grid Gross Loss

[grgmiller]

Our published carbon accounting emission factors do not yet consider transmission losses as part of the calculation, which would account for losses between the points of generation and points of consumption. As the eGRID technical guide notes:

because there are line losses, one kilowatt hour of electricity consumption requires a little more than one kilowatt hour of electricity generation. To account for transmission and distribution line losses when applying eGRID output emission rates to electricity consumption within a certain region, consumption is divided by (one minus the grid gross loss [as a decimal])

There are two places where it would make sense to account for these losses:

• when performing the physics-based reconciliation of EIA-930 data, the conservation of energy equation currently assumes that demand = generation + net interchange. However, in reality, this equation should be demand + transmission losses = generation + net interchange
• When calculating consumption-based emissions, we only use net generation and interchange data to calculate this, and ignore the demand data. However, if demand data were used as part of the calculation, this would in theory implicitly account for these losses.

Both of the above issues would need to be addressed in the gridemissions repository that we use in the pipeline.

One potential alternative (or perhaps more appropriately a short-term patch) would be to apply a BA-specific grid gross loss value to our consumption-based factors as a post-processing step.

Calculating Grid Gross Loss

eGRID uses data from the EIA's State Electricity Profiles and EIA-861 to calculate grid gross loss values at the interconnect level. See section 3.5 of the eGRID technical guide for a full overview of the methodology. We should look into whether it is possible to calculate these factors at the BA-level.

[grgmiller]

Electricity disposition data is reported by utility in the "Operational_Data" table of EIA-861. This table only reports the NERC region of each utility, but we may be able to map the utility to BA using one of the other EIA-861 tables, like "Sales_Ult_Cust".

[grgmiller]

Based on the work started in #161, this is what I've discovered so far:

How does eGRID Calculate GGL?

• eGRID calculates GGL based on the EIA's State Electricity Profiles, specifically using Table 10, which includes calculated supply and disposition for each state. These values are calculated by EIA using the data reported in EIA-861 (which is reported by utility).
• The formula for GGL is GGL = Losses / (Disposition - Exports - Direct Use), where:
  • Disposition is equivalent to the total supply, including sales, losses, and self-use
  • Exports is electricity exported to other states. eGRID notes that it excludes exports due to a "slight double counting" issue, but I'm not really clear how exactly this causes an issue.
  • Direct use is the total amount of electricity consumed by the utility itself, and not sold for resale. eGRID interprets direct use to mean station use (ie the difference between gross and net generation), noting in their documentation that "direct use electricity is not transmitted through the grid and therefore does not have the potential to be lost". However, EIA notes in the footnotes to Table 10 that "Direct use is exclusive of station use." Thus I believe this to be a source of error in eGRID's method.
  • Losses are essentially total supply minus total sales or consumption by end uses
• Because state boundaries do not correspond exactly with interconnect boundaries, they have to allocate the data from the state profiles in proportion to the net generation reported in each state/interconnect in EIA-923.

How does this PR calculate GGL?

• My goal was to calculate GGL values for each BA, rather than at the interconnect level. Disposition data is reported for each utility in the EIA-861 "Operational Data" table. However, utilities sometimes serve load in multiple balancing authorities, so I needed a way to allocate the disposition data from each utility to each BA.
• Utilities separately report their total retail sales (which is a component of total disposition) in each BA in the EIA-861 "Sales_Ult_Cust" tables. I use this data to calculate which fraction of each utility's total retail sales are in each BA, and then distribute the utility disposition data to each BA based on this fraction.
• The formula that I use to calculate GGL is GGL = Losses / Disposition. I don't subtract out direct use (called "consumed by respondent without charge" in EIA-861) due to the note above, and I don't subtract out exports, because there is not a clear reason upon examining the data why this should be exlcluded from total disposition (although this is something that we should look into). I'm wondering if the total state export data in the state electricity profile is different from the "exchange energy delivered" data in EIA-861, and thus there might be a reason to treat it differently.
• This method results in GGL values between 0% and 10% for individual BAs, which seems reasonable.
• After this allocation, the total disposition and losses (for the whole country) still matches the total disposition and losses reported in the raw EIA-861 form.

Why are our calculations so different from eGRID?

• eGRID reports a national average GGL of 5.3%, with a range of 5.2%-5.6% across all interconnects. By comparison, the national average GGL we calculate is 2.7% with a range of 0% to 9.7%. It is concerning that the national average value that we calculate is about half of that that eGRID calculates.
• Even if I use the raw EIA-861 disposition data and try to calculate a national GGL using eGRID's formula (GGL = Total Energy Losses / (Total Disposition - Exchange Energy Delivered - Consumed by Respondent without Charge)) I still only arrive at a national average value of 2.8%.
• My suspicion is that there is double counting somewhere in one of our approaches
  • it is possible in my approach that I need to somehow adjust total disposition or losses. This would require either doubling total losses or halving total disposition. Total disposition in 2020 was about 7.5 billion MWh, which means to get a loss of 5%, I'd need to decrease disposition by about 3.8 billion MWh. The only other values in the disposition table that are close to this are retail sales (3.6 billion) sales for resale (3.6 billion). This makes me wonder if maybe the disposition value in the state profile excludes sales for resale.
  • After taking a look at the state profiles, it looks like these might exclude sales for resale in the total disposition numbers, while EIA-861 includes these resales in total disposition. The instructions for EIA-861 note that sales for resale includes "sales for resale to power marketers (reported separately in previous years), full and partial requirements customers, firm power customers, and non-firm customers". the EIA-861 table does include disposition data for retail power marketers (and wholesale power marketers), so I am wondering if there is some double-counting of disposition.