Natural Gas Sector

Overview

PyPSA-USA models the natural gas network at a state level - as the EIA reports gas data at a state levels. The addition of the gas network happens after the builing of the electrical network (including clustering).

Included in the natural gas netowrk is state level pipelines, state-to-state pipeline capacity, state level import/export capacity by point-of-entry, facility level underground storage limits, and state level gas-processing capacity. Additionally, users can choose to enforce domestic and international import/export limits to states/provinces outside of the model scope, matching historical trade volumes. Methane tracking is represented as a function of total injected natural gas into the system, with configurable leakage rates and global warming potentials.

Note

Only dry natural gas is tracked, not LNG.

Model Implementation

This section will give details on how natural gas is modelled within PyPSA-USA.

Spatial Representation

The natural gas network is represented at a state level, as EIA Natural Gas data is often reported at state levels. The gas network is overlaid on the electrical sector, not changing the clustering done upstream in the workflow. Central state-level gas buses are created to facilitate the transportation and consumption of gas. Natural gas generators (for example combined-cycle and open-cycle gas turbines) retain all technical and economic paramters, but are changed to connect to the state level bus.

Consider the two state model shown below. State X has 3 clustered regions and 2 natural gas generators, while state Y has 2 clustered regions and 2 natural gas generators. Each clustered node may have other generators, loads, and connections, not shown here for simplicity. Figure 1 shows how the electrical sector will create the network. Figure 2 shows how the natural gas modifies the network. The other components (such as pipelines and gas processing) are described in the next section.

Electrical Network Spatial Representation

Electrical and Gas Networks Spatial Representation

PyPSA Representation

The natural gas network includes the following components. All components attach a the central state level natural gas bus. The following figure shows how the different components connect.

Component	Operational Constraints	PyPSA-Component
Underground Storage	Min/Max storage levels | Capacity	Store + Links + Bus
Pipelines	Capacity	Links
Linepack	Min/Max storage levels	Store
Processing	Capacity	Store + Links + Bus
Import/Exports	Capacity | Annual Energy	Store + Links + Bus

Natural Gas Network Components

Import/Exports

Regions outside the model scope include connections to neighbouring states (for USA), provinces (for Canada), or countries (for Mexico). For example, if a model of Washington, Oregon, and California is run, the following import/export connections will be made. If no pipeline exisits between the regions, or is one-directional, the capacity is set to zero.

Modelled Region	Connecting Region	Type
Washington	British Columbia	International
Washington	Idaho	Domestic
Oregon	Nevada	Domestic
California	Nevada	Domestic
California	Arizona	Domestic
California	Mexico	International

Additionally, the user can choose to enforce boundary conditions on these connections. If applied, annual historical imports and exports to the neighbouring regions are retrieved from the EIA for the modelled weather year. Minimum and maximum import/export constraints based on this reference value can then be specified through the following configuration file.

Consider the schematic below, showing how a single state is trading with a neighbouring state outside the models geographic scope. Assume that the historical year imports and exports are 10000 MMCF in both directions. The following table shows how the user can specify import/export limits into and out of each state. Note, the constraints are applied at a state level, but each state must respect the same constraint configuration values.

Simple Natural Gas Trading with Regions Outside Model Scope

Configuration Option	Configuration Value	Description	Constraint	Applied to
import.min	0	No import requirement	Σ(p) >= 0	S2 S1 gas trade
	0.5	Import at least half of historical year value	Σ(p) >= 5000	S2 S1 gas trade
	1	Import at least historical year value	Σ(p) >= 10000	S2 S1 gas trade
	2	Import at least double the historical year value	Σ(p) >= 20000	S2 S1 gas trade
import.max	0	No imports allowed	Σ(p) <= 0	S2 S1 gas trade
	0.5	Import up to half of historical year value	Σ(p) <= 5000	S2 S1 gas trade
	1	Import up to the historical year value	Σ(p) <= 10000	S2 S1 gas trade
	2	Import up to double the historical year value	Σ(p) <= 20000	S2 S1 gas trade
	inf	Unlimited Imports	No constraint added	S2 S1 gas trade
export.min	0	No exports requirement	Σ(p) >= 0	S1 S2 gas trade
	0.5	Export at least half of historical year value	Σ(p) >= 5000	S1 S2 gas trade
	1	Export at least the historical year value	Σ(p) >= 10000	S1 S2 gas trade
	2	Export at least double the historical year value	Σ(p) >= 20000	S1 S2 gas trade
export.max	0	No exports allowed	Σ(p) <= 0	S1 S2 gas trade
	0.5	Export up to half of historical year value	Σ(p) <= 5000	S1 S2 gas trade
	1	Export up to the historical year value	Σ(p) <= 10000	S1 S2 gas trade
	2	Export up to double the historical year value	Σ(p) <= 20000	S1 S2 gas trade
	inf	Unlimited Export	No constraint added	S1 S2 gas trade

Capacity Expansion

PyPSA-USA does not currently support natural gas pipeline expansion and retrofitting.

Methane Tracking

Leaks in the natural gas system are often categorized into upstream and downstream leaks. Upstream leaks inclde leaks from production and processing. Downstream leaks include leaks from transportation, falaring, and incomplete fuel combustion. PyPSA-USA allows users to specify both upstream and downstream leakage rates as a percentage of natural gas usage. Moreover, a global warming potential is applied to the leaked gas the represent the intensity of methane compared to carbon dioxide over different time-frames. The follow figure graphically shows how methane is accounted in PyPSA-USA.

Upstream Methane Tracking in PyPSA-USA

Data Sources

Listed below are the main datasources and assumptions applied to them to build the natural gas network.

Data	Source	Assumptions
State-to-State Pipeline Capacity	EIA Natural Gas	All currently installed pipelines will not be retired before 2050.
State Level Transmission Pipeline Volume	HIFLD	Includes both interstate and intrastate pipelines. Piepline operating pressures. Pipeline diameters.
State Level Gas Processing	EIA Natural Gas Gross Withdrawals and Production	Marketed dry natural gas production.
State Level Underground Storage	EIA Underground Natural Gas Storage Capacity	Starting level state of charge. Includes salt cavers, depleted fields, and aquifers. Not extendable.
State Level Domestic Imports/Exports	EIA International & Interstate Movements of Natural Gas by State
State Level International Imports/Exports	EIA U.S. Natural Gas Imports by Point of Entry	A state can only trade with one other province. If the sate is connected to two provinces, the larger capacity connection is taken as the connection.
Gas Extraction Marginal Costs	Alberta Energy Regulator	Costs do not depend on well type

Validation

Note

Sector coupling studies are all under active development. More info to come!