Downstream Emissions

Contents

Overview | Asset Structure | Flow Equations | Input File (Standard Format) | Types - Asset Structure | Constructors | Examples | Best Practices | Input File (Advanced Format)

Overview

Downstream emissions assets in Macro represent end-use commodity consumption processes at the downstream end of a value chain. They take in a commodity from the modeled system, pass that commodity to a demand or consuming node, and emit CO2 according to an emission_rate. These assets are defined using either JSON or CSV input files placed in the assets directory, typically named with descriptive identifiers like downstreamemissions.json or downstreamemissions.csv.

This asset is intended for cases where the commodity is routed to an external node that already exists in the system, including cases where several assets share the same downstream demand node. In other words, DownstreamEmissions adds emissions to a shared downstream node rather than owning a dedicated demand node internally.

The current implementation is generic over commodity type, so the same asset can represent downstream emissions from liquid fuels, natural gas, or other commodities supported by the model.

This distinction is important relative to the planned DownstreamUse asset: DownstreamEmissions routes flow to an external node via fuel_demand_end_vertex, whereas DownstreamUse is intended for cases where the asset itself will include a demand node.

For backward compatibility, DownstreamUse and FuelsEndUse remain available as aliases of DownstreamEmissions.

Asset Structure

A downstream emissions asset consists of four main components:

1. Transformation Component: Balances commodity throughput and emissions
2. Fuel Edge: Represents the incoming commodity flow from the modeled system
3. Fuel Demand Edge: Represents the outgoing commodity flow to an external end-use or demand node
4. CO2 Edge: Represents emitted CO2 sent to a sink or location

DownstreamEmissions does not create its own node. The outgoing fuel_demand_edge must connect to a node that is already defined elsewhere in the system.

Here is a graphical representation of the downstream emissions asset:

Flow Equations

The downstream emissions asset follows these relationships:

\[\begin{aligned} \text{flow}_{fuel\_demand} &= \text{flow}_{fuel} \\ \text{flow}_{co2} &= \text{flow}_{fuel} \cdot \epsilon_{emission\_rate} \end{aligned}\]

Where:

• $flow$ represents the flow of each commodity
• $\epsilon$ represents the emission coefficient defined in the Conversion Process Parameters section

Input File (Standard Format)

The easiest way to include a downstream emissions asset in a model is to create a new file (either JSON or CSV) and place it in the assets directory together with the other assets.

Because this asset does not contain its own demand node, the fuel_demand_end_vertex should point to an existing node in nodes.json or to another node created elsewhere in the case definition.

your_case/
├── assets/
│   ├── downstreamemissions.json    # or downstreamemissions.csv
│   ├── other_assets.json
│   └── ...
├── system/
├── settings/
└── ...

This file can either be created manually, or using the template_asset function, as shown in the Adding an Asset to a System section of the User Guide. The file will be automatically loaded when you run your Macro model.

The following is an example of a downstream emissions asset input file:

{
    "downstream_emissions": [
        {
            "type": "DownstreamEmissions",
            "instance_data": [
                {
                    "id": "liquid_fuels_use_SE",
                    "location": "SE",
                    "fuel_commodity": "LiquidFuels",
                    "fuel_demand_commodity": "LiquidFuels",
                    "fuel_demand_end_vertex": "liquid_fuels_demand_SE",
                    "emission_rate": 0.25,
                    "fuel_demand_investment_cost": 2500,
                    "fuel_demand_fixed_om_cost": 100,
                    "fuel_demand_variable_om_cost": 2.0,
                    "co2_sink": "co2_atm_SE"
                }
            ]
        }
    ]
}

The following tables outline the attributes that can be set for a downstream emissions asset.

Essential Attributes

Conversion Process Parameters

Simple-format edge attributes use edge-specific prefixes. For example, incoming commodity edge fields are written as fuel_investment_cost, fuel_existing_capacity, and fuel_constraints; outgoing demand edge fields use the fuel_demand_ prefix; and CO2 edge fields use the co2_ prefix.

Constraints Configuration

Downstream emissions assets can have different constraints applied to them, and the user can configure them using the following fields:

Users can refer to the Adding Asset Constraints to a System section of the User Guide for a list of all the constraints that can be applied to a downstream emissions asset.

Default constraints

To simplify the input file and the asset configuration, the following constraints are applied to the downstream emissions asset by default:

• Balance constraint (applied to the transformation component)

Investment Parameters

Additional Investment Parameters

If MaxCapacityConstraint or MinCapacityConstraint are added to the constraints dictionary for the outgoing demand edge, the following parameters are used by Macro:

Economic Parameters

Operational Parameters

Additional Operational Parameters

If MinFlowConstraint is added to the constraints dictionary for the outgoing demand edge, the following parameter is used:

If RampingLimitConstraint is added to the constraints dictionary for the outgoing demand edge, the following parameters are used:

Types - Asset Structure

The DownstreamEmissions asset is defined as follows:

struct DownstreamEmissions{T} <: AbstractAsset
    id::AssetId
    fuelsenduse_transform::Transformation
    fuel_edge::Edge{<:T}
    fuel_demand_edge::Edge{<:T}
    co2_edge::Edge{<:CO2}
end

const DownstreamUse = DownstreamEmissions
const FuelsEndUse = DownstreamEmissions

Constructors

Default constructor

DownstreamEmissions(
    id::AssetId,
    fuelsenduse_transform::Transformation,
    fuel_edge::Edge{T},
    fuel_demand_edge::Edge{T},
    co2_edge::Edge{<:CO2}
) where T<:Commodity

Factory constructor

make(asset_type::Type{DownstreamEmissions}, data::AbstractDict{Symbol,Any}, system::System)

Examples

This section contains examples of how to use the downstream emissions asset in a Macro model.

Multiple downstream emissions assets with shared defaults

This example shows how to create two downstream emissions assets in different zones with shared global data and zone-specific emission_rate and cost assumptions. Both assets route flow to an external demand node rather than owning separate internal demand nodes.

JSON Format:

{
    "downstream_emissions": [
        {
            "type": "DownstreamEmissions",
            "global_data": {
                "fuel_commodity": "NaturalGas",
                "fuel_demand_commodity": "NaturalGas",
                "fuel_demand_end_vertex": "natgas_demand",
                "fuel_demand_variable_om_cost": 1.0,
                "co2_sink": "co2_atm"
            },
            "instance_data": [
                {
                    "id": "natgas_use_SE",
                    "location": "SE",
                    "emission_rate": 0.18,
                    "fuel_demand_investment_cost": 1200,
                    "fuel_demand_fixed_om_cost": 80
                },
                {
                    "id": "natgas_use_NE",
                    "location": "NE",
                    "emission_rate": 0.16,
                    "fuel_demand_investment_cost": 1500,
                    "fuel_demand_fixed_om_cost": 95
                }
            ]
        }
    ]
}

CSV Format:

Best Practices

1. Use explicit commodity names for both fuel_commodity and fuel_demand_commodity, even when they are the same.
2. Set fuel_demand_end_vertex explicitly so the outgoing demand flow is routed to the intended external node.
3. Use this asset when several emitting processes should connect to the same shared downstream node.
4. Set co2_sink explicitly when emissions should be routed to a dedicated CO2 node rather than the asset location.
5. Keep emission_rate units consistent with the commodity flow units used in the rest of the model.
6. Use global_data for shared cost and commodity settings when creating many downstream emissions assets.

Input File (Advanced Format)

Macro provides an advanced format for defining downstream emissions assets, offering users and modelers detailed control over transformation and edge specifications.

To understand the advanced format, consider the graph representation and the type definition of a downstream emissions asset. The input file mirrors this hierarchical structure.

A downstream emissions asset in Macro is composed of a Transformation object and three Edge objects. The input file for a downstream emissions asset is therefore organized as follows:

{
    "transforms": {
        // ... transformation-specific attributes ...
    },
    "edges": {
        "fuel_edge": {
            // ... incoming commodity edge-specific attributes ...
        },
        "fuel_demand_edge": {
            // ... outgoing demand edge-specific attributes ...
        },
        "co2_edge": {
            // ... CO2 edge-specific attributes ...
        }
    }
}

Below is an example of an advanced input file for a downstream emissions asset:

{
    "downstream_emissions": [
        {
            "type": "DownstreamEmissions",
            "instance_data": [
                {
                    "id": "liquid_fuels_use_SE",
                    "location": "SE",
                    "transforms": {
                        "timedata": "LiquidFuels",
                        "emission_rate": 0.25,
                        "constraints": {
                            "BalanceConstraint": true
                        }
                    },
                    "edges": {
                        "fuel_edge": {
                            "commodity": "LiquidFuels",
                            "start_vertex": "liquid_fuels_SE"
                        },
                        "fuel_demand_edge": {
                            "commodity": "LiquidFuels",
                            "end_vertex": "liquid_fuels_demand_SE",
                            "investment_cost": 2500,
                            "fixed_om_cost": 100,
                            "variable_om_cost": 2.0
                        },
                        "co2_edge": {
                            "commodity": "CO2",
                            "end_vertex": "co2_atm_SE"
                        }
                    }
                }
            ]
        }
    ]
}

Key Points

• The transforms block configures the internal transformation object, including timedata, constraints, and emission_rate.
• The fuel_edge and fuel_demand_edge can be assigned any supported commodity type, allowing the asset to model downstream emissions for multiple sectors.
• The co2_edge always uses the CO2 commodity and can terminate either at co2_sink or at the asset location.
• For a comprehensive list of attributes that can be configured for edges and transformations, refer to the edges and transformations pages of the Macro manual.