Improve Marginal (Price-Setter) Methodology

[dec-heim]

Suggested Improvements to Marginal Emissions Methodology (specifically how data is treated from price setter files).

To be reviewed....

Current Issue:
The price setter file 'Increase' column is indicative of MLFs not the actual MW increase in power from a marginal generator. Current method however weights marginal emissions intensity for a 5-min DI by the increase factors. This results in overcounting (quite high emissions factors >> 1tCO2/MWh for some DIs) while also undercounting in other intervals.

Proposed Method:

1. Cleaning for ‘Increase’ amounts only over 0.05MW (to represent significant influences on the margin, price setter files includes some minor curtailed/varied generation)
2. Resampling using the mean of the ‘Intensity_Index’ in that Time-Region
3. ‘CO2E_ENERGY_SOURCE’ as multiple unit energy sources for that Time-Region (e.g. Hydro, Natural Gas (Pipeline) rather than a single technology.

Additional changes to consider:

• Optional setting to consider Hydro/Storages in step 2 (mean of 'Intensity_Index') or not. For example if both Hydro (0tCO2/MWh) and Gas (~0.6tCO2/MWh) are marginal generators in the same DI/region. Instead of averaging their intensities which would yield
  0.3tCO2/MWh (a factor half of the actual gas emissions intensity), this setting would simply adopt the mean emissions intensities excluding hydro (therefore 0.6tCO2/MWh). Where hydro is the only generator on the margin in a single DI/region, the emissions factors should remain that of the hydro plant (e.g. 0tCO2/MWh).

Note the above additional filter is more a makeshift workaround to mitigate 0tCO2/MWh factors from distorting emissions observations but does not intend to completely offer a solution for substituting different emissions factors where hydro/storage is on the marginal.

Credits
Credit to Louise Bardwell for picking up this issue and contributing proposed solution.

For reference:

https://wattclarity.com.au/articles/2019/02/a-preliminary-intermediate-guide-to-how-prices-are-set-in-the-nem/
https://wattclarity.com.au/articles/2019/03/price-setting-concepts-an-explainer/