Release Notes

v0.3.0 (2026-10-06)

Summary of breaking changes

• Requires EnergyModelsBase v0.10.
• The source-attribution pooling variables proportion_source and proportion_track are replaced by flow_component on blend links and proportion_out at pooling nodes.
• The lower_pressure_into_node binary is removed, and has_flow is only declared for pressure-carrying links.
• Passthrough nodes (e.g. TransitNode) send blend down at most one outgoing link per period.
• proportion_out is only defined at the nodes that need the composition (see "Composition tracked only where needed"), no longer at sinks, unit conversions and passthrough nodes in general. Use flow_component on the links instead.
• Storage of a blended resource requires BlendStorageData, which chooses how the composition of the discharged gas is modelled. A blend storage without it is rejected.

Composition tracked only where needed

• The component flows give the composition wherever blend mixes. The share proportion_out is only created at composition sources (pooling nodes, blend storages in mode :prescribed or :fully_mixed) and at the nodes from which a Weymouth pipe with BlendLinkData reads it (blend_share_plan).
• A merge no longer forces simultaneous inflows to have the same composition, unless a Weymouth pipe downstream reads the share through it.
• A Weymouth pipe may read the share from its outflow end: from the first pooling node downstream, if the pipe is its only blend inflow. A BlendingNode may then feed the pipe directly.
• A passthrough node with several outgoing blend links no longer needs a share from upstream; it only needs has_flow on all of them (one active outflow per period).

Blend storage

• New BlendStorageData for Storage nodes that store a ResourcePooling blend. The storage keeps one inventory per component (stor_level_component), following the level balance and cyclic constraints of EnergyModelsBase, so the storage can not discharge more of a component than was charged.
• The discharge composition depends on the mode, which must be given:
  • :relaxed only bounds the discharge by the inventories (linear);
  • :prescribed follows an extraction quality profile (linear);
  • :fully_mixed discharges the average stored composition (bilinear). It suits small, well-mixed storages, not depleted gas reservoirs.
• Storages no longer copy the composition of their charge within the same period.

PWA robustness

• PWA fits are seeded from the cache key and checked against the exact Weymouth flow; degenerate fits are refitted and never cached.
• get_pwa throws an ArgumentError when the pressure step leaves fewer than three pressure levels in the range of a link, instead of failing in the fit.
• Blend links without BlendLinkData use the Taylor cuts without requiring the PWA optimizer to be set.

Breaking: passthrough nodes send blend down one link per period

TransitNodes, and other NetworkNodes that pass a blend through unchanged, may now only send blend down one outgoing link in each period. The linear passthrough did not force the outgoing links to share the node's composition, so a split could send different mixtures down each link.

• With several outgoing blend links, Σ has_flow[l_out, t] ≤ 1 is added. Bidirectional pipelines are still supported, since only one direction carries flow.
• If any of those links has no has_flow binary tied to its flow (no pressure resource), validate_blend_topology raises an ArgumentError.
• Use PoolingNode or DiscretizedPoolingNode where the blend must split into several pipes at the same time.

Pooling formulation: reduced bilinear complexity

The pooling formulation has been revised to reduce nonlinear complexity relative to the earlier Alfaki & Haugland (2013) S-formulation, which introduced bilinear products $y^s_j \times f_{(j,t)}$ scaling with the number of sources, arcs, and time periods.

The revised approach uses the P-formulation variable proportion_out[n, t, p] (fraction of component p in the blend leaving node n at time t). Bilinear products proportion_out × link_in scale with the number of pooling nodes and blend components, which is substantially smaller for typical gas network models with few blend components. Three specialised node types further reduce or eliminate the remaining bilinear terms:

BlendingNode — linear single-output mixing node

A new node type BlendingNode replaces PoolingNode at junctions with exactly one outgoing blend link. It uses a linear formulation:

• No proportion_out variable is declared for BlendingNode nodes.
• Component balance (flow_component[l_out] = Σ_in flow_component[l_in] + raw_in) is already linear and fully determines the output composition.
• Quality bounds (flow_component[l_out, H2] ≤ max_h2 × link_in[l_out, Blend]) remain linear because max_h2 is a fixed parameter, not a variable.

This eliminates bilinear constraints at all single-output mixing junctions (pre-sink, post-source, single-path transit mixing), which represent the majority of pooling nodes in typical gas network cases:

Usage: Use BlendingNode wherever a mixing node has exactly one ResourcePooling output. Use PoolingNode when two or more output blend links must share the same composition. Case checking rejects a BlendingNode whose output dict has more than one ResourcePooling blend, and validate_blend_topology raises an ArgumentError if a BlendingNode feeds two or more outgoing blend links.

DiscretizedPoolingNode — MILP-compatible piecewise-linear pooling

A new node type DiscretizedPoolingNode replaces the bilinear product at multi-output pooling nodes with a piecewise-linear MILP approximation via PiecewiseLinearOpt.jl. The approximation divides both the proportion and flow axes into intervals controlled by DiscretizationData. The model remains a MILP throughout and can be solved by standard solvers (HiGHS, Xpress, Gurobi) without MINLP machinery.

DiscretizationData now accepts an explicit tracked blend component. This removes the previous dependence on subresource ordering and allows a restricted discretization range to be applied only to the tracked component. Legacy constructors remain supported when the tracked component can be inferred unambiguously from adjacent blend-quality data.

DeblendNode — hydrogen extraction processing facility

A new node type DeblendNode models on-site separation of a component (e.g., H₂) from a blend stream, representing processing facilities such as pressure-swing adsorption (PSA) units. Unlike mixing nodes, DeblendNode applies a separation operation: the extracted component flow is bounded by psa_efficiency × incoming_component_flow. All constraints are linear. This extends the pooling formulation to networks that include in-network gas processing, following the generalised pooling framework of Hellemo & Tomasgard (2016, TOP 24:409–444).

FlowPressureCompressor — flow- and pressure-dependent compressor power

A new compressor type FlowPressureCompressor extends SimpleCompressor with power consumption that depends linearly on both the gas flow rate and the pressure increase:

Power ≥ flow_weight × cap_use + pressure_weight × potential_Δ

This is physically more accurate than SimpleCompressor (which ignores flow rate) for compressors operating over a range of flow conditions. The flow_weight and pressure_weight coefficients are computed from the physical design point using the linearisation formula described in the FlowPressureCompressor docstring.

Binary variable simplification

The lower_pressure_into_node binary array has been removed. Pressure-coupling at nodes with multiple incoming links now uses has_flow as the big-M switch for both the upper and lower bounds on potential_in[n]. When has_flow[l,t]=1 both bounds bind, forcing potential_in[n] = link_potential_out[l] for every active link.

For parallel investment pipeline options connecting the same two nodes, this means all active options see the same endpoint pressures — physically correct junction behaviour assuming pressure reduction valves harmonise any pressure differences. The previous sum(lower_pressure_into_node) ≤ 1 coupling constraint is eliminated, removing an artificial restriction that prevented correct selection among parallel pipeline options.

has_flow is still declared only for pressure-carrying links — those whose link_res includes at least one CompoundResource (ResourcePressure or ResourcePooling{<:ResourcePressure}). Power-only links remain excluded.

The capacity big-M now uses the maximum possible installed link capacity rather than the initial physical capacity. Investable pressure links can therefore use capacity added during the study without weakening the time-dependent link_cap_inst constraint.

Supported topology boundaries

A storage of a blend needs BlendStorageData and a Cyclic storage behaviour. Storages in mode :prescribed or :fully_mixed set the composition of their discharge and may feed several links and BlendLinkData links; storages in mode :relaxed may not.

BlendingNode and DeblendNode retain fully linear component-flow formulations and do not define proportion_out. Their output may feed single-output blend paths, and a Weymouth pipe with BlendLinkData only if the pipe is the only blend inflow of a pooling node downstream. Use PoolingNode or DiscretizedPoolingNode where a composition must be shared over several simultaneous outflows or a Weymouth pipe needs it.

v0.2.0 - v0.2.2

• Release the first version of EnergyModelsGasNetworks publicly after development phase.
• Version aligned with the current EnergyModelsBase branch enhance/transfer_energy_potentials (date: 26/02/2026). Updates will be required when the corresponding branch is merged into the main branch.