Add direct emissions method with data export

docs/contrib/direct-emissions-method.md

@@ -0,0 +1,147 @@
+---
+title: Direct emissions method
+---
+
+The direct emissions method determines the greenhouse gas emissions of a scenario at the point where emissions are released. Go to [direct emissions](../main/direct-emissions.md) for more information about the general principles of this method. The current page gives the technical background of how the direct emissions method works. 
+
+## Technical principles
+The direct emissions method distinguishes methods for determining CO2 flows for **energy nodes**, as well as methods to determine reporting greenhouse gas emissions (CO2, other GHG and total GHG) calculated for both **energy nodes** and **molecule nodes**. These different methods are further explained below. 
+
+Note that all of the direct emissions methods are only calculated for energy and molecule nodes that have the `emissions` group specified. All emissions are calculated in `kg CO2eq`.
+
+## CO2 flow methods
+The ingoing and outgoing CO2 flows depicted in the diagram below are calculated for **energy nodes**. The method calculates these flows for both fossil and biogenic CO2. These flows are the building blocks for calculating the reporting greenhouse gas emissions. The following subsections explain how each of the flows, indicated with letters A-E, are calculated. The method keys for querying the respective CO2 flow on nodes are provided as well.
+
+![](/img/docs/direct_emissions_co2_flows_letters.png)
+***Figure**. Incoming and outgoing CO2 flows of a technology.*
+
+### CO2 content input carriers (A) 
+This flow represents ingoing CO2 embedded in input carriers. The flow is calculated for each ingoing edge, multiplying the demand of that edge with the carrier's emission factor. 
+
+```
+A = Σ( input_edge.demand × carrier.co2_per_mj )
+``` 
+Method keys:  
+`direct_co2_input_content_carriers_fossil`  
+`direct_co2_input_content_carriers_biogenic`
+
+
+### CO2 utilisation (B)
+This flow represents used CO2 on the node, for example for production of synthetic transport fuels. The required CO2 is determined based on the useful output of a node multiplied with `co2_utilisation_per_mj`. Note that this is the only flow that is not calculated for biogenic CO2 as the ETM only has processes where non-biogenic carriers are produced from CO2 utilisation. 
+
+```
+B = Σ( edge.output ) × node.co2_utilisation_per_mj 
+```
+Method key:  
+`direct_co2_input_utilisation_fossil`
+
+### CO2 content output carriers (C)
+This flow represents outgoing CO2 embedded in output carriers. The flow is calculated for each outgoing edge, multiplying the energy flow with the carrier's emission factor. 
+
+```
+C = Σ( output_edge.demand × carrier.co2_per_mj )
+```
+Method key:  
+`direct_co2_output_content_carriers_fossil`  
+`direct_co2_output_content_carriers_biogenic`
+
+### CO2 capture (D)
+This flow represents the amount of captured CO2 on the node. The flow is determined based on the gross produced CO2 and the `ccs_capture_rate` specified for that node. The gross produced CO2 is the difference between ingoing CO2 (embedded in input carriers `A` and CO2 utilisation `B`) and outgoing CO2 embedded in output carriers `C`.
+
+```
+co2_production = A + B - C
+D = co2_production * ccs_capture_rate
+```
+Method keys:  
+`direct_co2_output_production_capture_fossil`  
+`direct_co2_output_production_capture_biogenic`
+
+### CO2 emissions (E)
+This flow represents the actual emitted CO2 and is the difference between the ingoing and outgoing CO2 flows described above. 
+
+```
+E = (A + B) - (C + D)
+```
+Method keys:  
+`direct_co2_output_production_emissions_fossil`  
+`direct_co2_output_production_emissions_biogenic`
+
+## Reporting emission methods
+The reporting greenhouse gas emission methods represent the relevant emissions that are typically reported by countries. These methods are used in the various user output for the direct emissions method (for example the data export). Note that these methods are queryable on both *energy nodes* and *molecule nodes*, but have a different implementation for these node types, which is further explained below.
+
+Four reporting emission methods are distinguished (inlcuding method key for querying the method):
+* CO2 production - `direct_reporting_emissions_co2_production`
+* CO2 capture - `direct_reporting_emissions_co2_capture`
+* Other GHG emissions - `direct_reporting_emissions_other_ghg_emissions`
+* Total GHG emissions - `direct_reporting_emissions_total_ghg_emissions`
+
+### CO2 production
+This represents the gross produced fossil CO2, before potential CO2 capture. 
+
+#### Energy node implementation
+It is determined from ingoing fossil CO2 (A + B) minus outgoing fossil CO2 embedded in output carriers (C). See the equation including the reporting method key below. 
+
+```
+direct_reporting_emissions_co2_production = 
+  direct_co2_input_content_carriers_fossil + 
+  direct_co2_input_utilisation_fossil -
+  direct_co2_output_content_carriers_fossil
+```
+#### Molecule node implementation
+There are molecule nodes that represent statically modelled CO2 emissions in the ETM by reading these CO2 flows from the dataset-specific `emissions.csv`. The method determines CO2 production based on the flow going through such nodes that have input of `co2`.
+
+### CO2 capture
+This represents the capture of both **fossil** and **biogenic** CO2.
+
+#### Energy node implementation
+Summing fossil and biogenic captured CO2:
+
+```
+direct_reporting_emissions_co2_capture = 
+  direct_co2_output_production_capture_fossil + 
+  direct_co2_output_production_capture_biogenic
+```
+
+#### Molecule node implementation
+It takes the CO2 demand of molecule nodes with group `ccus_captured`. Effectively, this means captured CO2 in industry (which is not modelled on the energy nodes), direct air capture and LULUCF CO2 removal are included. 
+
+### Other GHG emissions
+This flow represents other GHG emissions (for example CH4 and N2O), expressed in kg CO2-eq. It only has an implementation for molecule nodes as other GHG emissions are not dynamically calculated (note: it is queryable on energy nodes but always gives back zero). The method determines other GHG emissions based on the molecule nodes that have input of `other_ghg`, which is only the case for molecule nodes that read static emissions data from the `emissions.csv` file. 
+
+### Total GHG emissions
+This flow represents the total reporting GHG emissions. It is composed of the total gross CO2 production minus captured CO2 (which gives actual CO2 emitted) plus other GHG emissions. The implementation is the same for both energy and molecule nodes. 
+
+```
+direct_reporting_emissions_total_ghg_emissions = 
+  direct_reporting_emissions_co2_production -
+  direct_reporting_emissions_co2_capture +
+  direct_reporting_emissions_other_ghg_emissions
+```
+
+## Complete list of method keys
+Below is the complete list of the method keys already provided in the text above. 
+
+*CO2 flow methods - fossil*:
+```
+direct_co2_input_content_carriers_fossil
+direct_co2_input_utilisation_fossil
+direct_co2_output_content_carriers_fossil
+direct_co2_output_production_capture_fossil
+direct_co2_output_production_emissions_fossil
+```
+
+*CO2 flow methods - biogenic*:
+```
+direct_co2_input_content_carriers_biogenic
+direct_co2_output_content_carriers_biogenic
+direct_co2_output_production_capture_biogenic
+direct_co2_output_production_emissions_biogenic
+```
+
+*Reporting emission methods*:
+```
+direct_reporting_emissions_co2_production
+direct_reporting_emissions_co2_capture
+direct_reporting_emissions_other_ghg_emissions
+direct_reporting_emissions_total_ghg_emissions
+```

docs/main/co2-main-principles.md

@@ -4,6 +4,10 @@ title: Main principles
 
 In the ETM the total greenhouse gas emissions for both the present and future are calculated for scenarios. This page contains extra information on the modelling principles behind carbon emissions in the ETM.
 
+:::warning Beta release: direct emissions
+The documentation pages give information about the default emissions method of the ETM, based on primary energy demand. A new emissions method based on **direct energy demand** is currently in beta release. Read more about this direct emisisons method [here](direct-emissions).
+:::
+
 ## Emission categories
 The ETM makes a distinction between four 'types' of greenhouse gas emissions:
 1. **Energetic CO<sub>2</sub> emissions**. These emissions are calculated by the ETM based on the energy use in your scenario. In other words, they are the result of the choices made in the [Demand](https://energytransitionmodel.com/scenario/demand/households/population-and-housing-stock) and [Supply](https://energytransitionmodel.com/scenario/supply/electricity/coal-plants) sections of the model.
@@ -44,8 +48,8 @@ One exception to the primary emission method is for final demand of non-biogenic
 If additional feedstock is required in the production process for these liquid fuels, the related CO<sub>2</sub> emissions are accounted for using the primary emissions method and allocated to the energy sector.
 
 :::info Calculation example
-The transport sector has a final diesel demand of `100 [MJ]`. Diesel is produced via pyrolysis and pyrolysis-oil fractionation, which proportionally requires `50 [PJ]` of hydrogen for diesel production. This hydrogen is in turn produced via SMR, requiring `60 [PJ]` of natural gas. 
-The direct CO<sub>2</sub> emissions for diesel demand are allocated to the transport sector and equal `100 [MJ] * emission factor of diesel [kgCO2/MJ]`. The primary CO<sub>2</sub> emissions associated with hydrogen consumption in the production process are allocated to the energy sector and equal `60 [PJ] * emission factor of natural gas [kgCO2/MJ]`. 
+The transport sector has a final diesel demand of `100 [MJ]`. Diesel is produced via pyrolysis and pyrolysis-oil fractionation, which proportionally requires `50 [PJ]` of hydrogen for diesel production. This hydrogen is in turn produced via SMR, requiring `60 [PJ]` of natural gas.
+The direct CO<sub>2</sub> emissions for diesel demand are allocated to the transport sector and equal `100 [MJ] * emission factor of diesel [kgCO2/MJ]`. The primary CO<sub>2</sub> emissions associated with hydrogen consumption in the production process are allocated to the energy sector and equal `60 [PJ] * emission factor of natural gas [kgCO2/MJ]`.
 :::
 
 The emission factors for liquid fuels are region-specific and can be consulted in the [Dataset Manager](https://data.energytransitionmodel.com/). The liquid fuels for which direct emissions are calculated as an exception are the following:

docs/main/co2-negative-emissions.md

@@ -10,11 +10,9 @@ The ETM supports so-called 'negative' emissions. Negative emissions arise when m
     * Direct use of biomass in industry, for both feedstock and combustion
     * Biomass-fired power plants
 
-2. By using Direct Air Capture
+2. By using Direct Air Capture (DAC)
 
-You can make assumptions about this in the Emissions > ['CCUS'](https://pro.energytransitionmodel.com/scenario/emissions/ccus/capture-of-co2)
-
-Below, both routes are explained in more detail.
+You can make assumptions about this in the [CCUS](https://energytransitionmodel.com/scenario/emissions/ccus/capture-of-co2) section of the model. Below, both routes are explained in more detail.
 
 ## Negative emissions from biomass
 Using biomass to extract bioenergy, for example for the production of electricity and hydrogen, and subsequently capturing and storing the CO<sub>2</sub> emissions released in this process may result in a net decrease in atmospheric CO<sub>2</sub> levels. This is typically referred to as BECCS: bio-energy with carbon capture and storage.
@@ -26,9 +24,9 @@ The [IPCC](https://doi.org/10.1111%2Fgcbb.12514) estimates the global potential
 ## Negative emissions from Direct Air Capture
 Direct Air Capture (DAC) is a process of capturing CO<sub>2</sub> directly from the ambient air using electricity. If the electricity used is renewable, storing the captured CO<sub>2</sub> can lead to a net decrease in atmospheric CO<sub>2</sub> levels. The captured CO<sub>2</sub> can also be used for the production of carbon neutral fuels.
 
-Direct Air Capture is a promising technology to bring down global CO<sub>2</sub> levels in the atmosphere. However, it is also an energy intensive process. Since CO<sub>2</sub> in the ambient air is 'available' everywhere in the world, DAC capacity is likely to be installed in areas that will have very low (renewable) power costs.
+DAC is a promising technology to bring down global CO<sub>2</sub> levels in the atmosphere. However, it is also an energy intensive process. Since CO<sub>2</sub> in the ambient air is 'available' everywhere in the world, DAC capacity is likely to be installed in areas that will have very low (renewable) power costs.
 
 ## Bookkeeping
 Negative emissions are incorporated in the CO<sub>2</sub> calculation in the following way:
 * Negative emissions arising from the production of electricity or hydrogen are incorporated in the [emission factor](co2-emission-factors.md) of these carriers. Since the ETM allocates CO<sub>2</sub> to the sectors in which energy is _used_, this means that all sectors using electricity or hydrogen 'benefit' from these negative emissions. Using more electricity or hydrogen may result in lower or even net negative sector emissions.
-* CO<sub>2</sub> captured by Direct Air Capture is deducted from the Energy sector.
+* CO<sub>2</sub> captured by DAC is deducted from the Energy sector.