.. SPDX-FileCopyrightText: Contributors to gb-dispatch-model SPDX-License-Identifier: CC-BY-4.0 .. _system-transmission: ########################################## Transmission Components ########################################## This page describes how the electricity transmission network is represented in the model, including AC lines, DC interconnectors, offshore bus mapping, and transmission availability. Overview ======== The transmission network defines how power flows between buses in the model. It spans the internal GB meshed transmission system, the DC interconnectors linking GB to continental Europe and Ireland, and the AC and DC lines connecting European countries to one another. The network comprises two layers: - **AC lines**: The internal GB high-voltage transmission grid, built from the OpenStreetMap (OSM) pre-built network and clustered to model regions - **DC interconnectors**: Cross-border HVDC links connecting GB to neighbouring countries, sized by FES scenario and year Before clustering, offshore wind farm stub buses in the OSM network are remapped to their electrically connected onshore regional bus — see :doc:`data_cleaning` for details. Transmission **availability** is accounted for through monthly unavailability fractions derived from NESO operational reports, applied separately to the intra-GB network and cross-border interconnectors. .. _transmission-data-sources: Data Sources ============ The figure below gives a high-level view of the transmission pipeline: .. graphviz:: digraph { rankdir=LR; node [shape=box, style=filled]; osm [label="OSM pre-built\nnetwork", fillcolor="#B3D9FF"]; tyndp [label="ENTSO-E TYNDP\n(PyPSA-Eur)", fillcolor="#B3D9FF"]; neso_pdf [label="NESO transmission\navailability reports\n(PDF)", fillcolor="#B3D9FF"]; fes_plan [label="FES interconnector\ncommissioning plan\n(config)", fillcolor="#B3D9FF"]; regions [label="Merged region\nshapes", fillcolor="#FFFACD"]; busmap [label="Offshore busmap\n(stub → region)", fillcolor="#FFFACD"]; intercon [label="interconnectors_p_nom.csv\n(MW per year)", fillcolor="#FFFACD"]; avail_intra [label="intra_gb transmission\navailability (monthly)", fillcolor="#FFFACD"]; avail_inter [label="inter_gb transmission\navailability (monthly)", fillcolor="#FFFACD"]; network [label="PyPSA Network\n(Line, Link)", fillcolor="#90EE90", shape=ellipse]; osm -> busmap; regions -> busmap; osm -> network [label="AC lines\n(clustered)"]; tyndp -> network [label="intra-EU DC links"]; busmap -> network [label="offshore bus\nmapping"]; fes_plan -> intercon; regions -> intercon; intercon -> network [label="GB DC links\n(p_nom per year)"]; neso_pdf -> avail_intra; neso_pdf -> avail_inter; avail_intra -> network [label="line s_nom\nscaling"]; avail_inter -> network [label="link p_nom\nscaling"]; } OSM Pre-built Network — AC Grid Topology ----------------------------------------- The internal GB transmission grid topology is read from a `custom version of the OpenStreetMap (OSM) pre-built network `_ maintained by the PyPSA-Eur pipeline. The custom version extends the standard OSM extract to include voltage levels (132 kV, 275 kV, 400 kV) that are particularly relevant to the GB grid. The network is configured via ``electricity.base_network: osm`` and the specific OSM archive version is pinned under ``data.osm``. ENTSO-E TYNDP — Intra-EU DC Links ---------------------------------- DC links between European countries are sourced from the **ENTSO-E Ten-Year Network Development Plan (TYNDP)** as processed by the base PyPSA-Eur workflow (``build_tyndp_network`` rule). These links enter the model as part of the clustered base network and are not modified by any GB-specific rules. FES / Config — GB Cross-border Interconnector Commissioning Plan ---------------------------------------------------------------- GB cross-border DC interconnector capacities and their commissioning years are defined entirely in the configuration file under ``interconnectors``. Each interconnector entry specifies: - **Name**: project identifier - **Neighbour**: country it connects to (converted to ISO2 country code for the PyPSA bus) - **Capacity (MW)**: nominal power transfer capacity - **TYNDP project ID and years**: cross-reference to the ENTSO-E Ten-Year Network Development Plan for traceability - **Lat/lon**: approximate location of the GB connection point, used to assign the interconnector to the nearest model region The ``interconnectors.plan`` section maps each FES scenario to a list of active interconnector projects by year, reflecting that different FES pathways assume different build-out of cross-border capacity. Since the FES workbook does not detail which projects it has chosen to reach its optimal GB interconnector capacities, we have defined this list based on our best understanding of the available projects. See `our interconnector GitHub issue `_ for more details. NESO Transmission Availability Reports — Line Availability ----------------------------------------------------------- Monthly transmission unavailability fractions are extracted from the **NESO operational transmission availability PDF reports**, covering years configured in ``transmission_availability.years`` (default 2020–2024). Reports include: - **Intra-GB**: Planned and unplanned unavailability (as a percentage) for each of the three GB Transmission Owner (TO) zones — NGET, SPT, and SHETL - **Cross-border (interconnectors)**: Monthly unavailability percentage for each active interconnector project These percentages are averaged over the configured year range to produce a stable monthly availability profile that is then applied as a ``p_nom`` or ``s_nom`` scaling factor for the simulated year. .. _transmission-components: System Components ================= .. _transmission-ac-lines: .. _transmission-interconnectors: The table below lists the key PyPSA attributes for both transmission component types. AC lines (``n.lines``) represent the internal GB meshed grid, clustered from the OSM pre-built network. GB cross-border DC interconnectors (``n.links``, ``carrier = "DC"``) connect GB regional buses to neighbouring country buses and are sized by FES scenario and year. Intra-EU DC links (also ``n.links``) enter the model unchanged from the base PyPSA-Eur workflow via the ENTSO-E TYNDP and are not listed here. .. list-table:: PyPSA network component attributes — AC Lines and DC Interconnectors :header-rows: 1 :widths: 14 16 12 15 43 * - Component - Attribute - Static / Dynamic - Source - Notes * - ``Line`` - ``bus0``, ``bus1`` - Static - OSM + clustering - Regional AC buses at each end; assigned during the PyPSA-Eur clustering step * - ``Line`` - ``s_nom`` - Static - OSM - Thermal rating (MVA) before availability scaling; derived from OSM voltage and line type * - ``Line`` - ``x``, ``r`` - Static - OSM - Series reactance and resistance (p.u.) from OSM line type and length; used in power-flow calculations * - ``Line`` - ``num_parallel`` - Static - OSM - Number of parallel circuits; aggregated during clustering * - ``Line`` - ``type`` - Static - OSM - Standard line type string (e.g. ``"Al/St 240/40 2-bundle 380.0"``); determines per-unit-length impedance * - ``Line`` - ``s_nom_extendable`` - Static - Default (``False``) - Capacity is fixed; the model does not invest in new AC lines * - ``Line`` - ``s_nom_pu`` - Dynamic (hourly) - Workflow (NESO PDFs) — *not yet applied* - Hourly availability series derived by random-sampling the monthly TO-zone unavailability fraction with a fixed seed per zone. Currently processed but not applied to line ratings; the intent is to apply TO-zone availability to boundary transfer capabilities rather than individual line ``s_nom`` values (see :ref:`transmission-availability`) * - ``Link`` (DC) - ``bus0``, ``bus1`` - Static - Workflow (config + regions) - ``bus0`` is the GB regional AC bus nearest to the configured lat/lon; ``bus1`` is the AC bus of the neighbouring country * - ``Link`` (DC) - ``carrier`` - Static - Workflow - Set to ``"DC"`` for all GB cross-border interconnectors * - ``Link`` (DC) - ``p_nom`` - Static (per model year) - Workflow (FES config plan) - One-directional nameplate transfer capacity (MW); scenario- and year-dependent. Projects are accumulated forward in time so a commissioned link retains its capacity in all later years * - ``Link`` (DC) - ``p_min_pu`` - Static - Workflow (``-1``) - Set to ``-1`` to enable full bidirectional flow; combined with ``p_nom`` this allows power up to the nameplate rating in either direction * - ``Link`` (DC) - ``p_nom_extendable`` - Static - Default (``False``) - Capacity is fixed to the FES plan value; no investment in additional interconnector capacity * - ``Link`` (DC) - ``efficiency`` - Static - Default (``1``) - No transmission losses modelled * - ``Link`` (DC) - ``p_nom_pu`` - Dynamic (monthly) - Workflow (NESO PDFs) - Monthly availability fraction; a single value shared across all interconnectors per month, averaged over all projects and report years (see :ref:`transmission-availability`) .. _transmission-configuration: Configuration ============= Example interconnector option entry (one entry per project under ``interconnectors.options``): .. literalinclude:: ../../config/config.gb.2024.yaml :language: yaml :start-after: # [doc:interconnector-option-example-start] :end-before: # [doc:interconnector-option-example-end] Interconnector commissioning plan (maps FES scenarios to project lists by year): .. literalinclude:: ../../config/config.gb.2024.yaml :language: yaml :start-after: # [doc:interconnector-plan-start] :end-before: # [doc:interconnector-plan-end] Transmission availability data configuration: .. literalinclude:: ../../config/config.gb.2024.yaml :language: yaml :start-after: # [doc:transmission-availability-config-start] :end-before: # [doc:transmission-availability-config-end] .. _transmission-implementation-notes: Implementation Notes ==================== Data Processing Workflow ------------------------ The transmission system is built through a pipeline implemented in ``rules/gb-model/transmission.smk``: .. image:: img/transmission_workflow.svg :align: center .. note:: The graph above was generated using:: pixi run filtered_rulegraph \ "resources/GB/gb-model/HT/interconnectors_p_nom.csv \ resources/GB/gb-model/intra_gb_transmission_availability.csv \ resources/GB/gb-model/inter_gb_transmission_availability.csv \ resources/GB/gb-model/custom_busmap.csv \ -w fes_scenario -w year \ -f rules/gb-model/transmission.smk \ -s 10,8" \ "doc/gb-model/img/transmission_workflow.svg" The ``filtered_rulegraph`` task allows us to trim the full DAG to transmission-related rules only. 1. **Extract availability** (``extract_transmission_availability``): Parses each NESO PDF report using ``pdfplumber``, extracting monthly unavailability tables for each TO zone and each interconnector project 2. **Process availability** (``process_transmission_availability``): Averages monthly unavailability across report years; for intra-GB zones, converts means to hourly ``0/1`` series by random sampling (reproducible via fixed seeds); for interconnectors, retains the monthly mean directly 3. **Interconnector table** (``create_interconnectors_table``): Reads the ``interconnectors.plan`` for the active FES scenario, accumulates capacity year-by-year, assigns each project to a GB model region using lat/lon point-in-polygon matching, computes line geometry (shortest path to neighbour country region), and outputs a per-year ``p_nom`` CSV 4. **Offshore busmap** (``identify_regions_for_offshore_buses``): Traverses the OSM base network graph to identify offshore stub buses and maps them to their onshore regional bus; iterates until all multi-hop offshore chains are resolved .. _system-transmission-assumptions: Key Assumptions --------------- - **Uniform zone availability**: Intra-GB availability is applied at the TO zone level (NGET, SPTL, SHETL); individual line ratings within a zone are not differentiated - **Interconnector availability**: A single aggregate monthly fraction is used for all interconnectors, averaged over all projects and report years - **Reproducible random sampling**: Hourly availability realisation uses fixed random seeds per zone to ensure model results are reproducible across runs - **Cumulative commissioning**: Interconnector capacities are accumulated forward in time — a project appearing in any year's plan remains active for all later years - **Country scope filtering**: Interconnectors to countries not in the ``countries`` list are excluded; the model logs excluded projects at INFO level - **No new intra-GB lines**: No additional AC transmission lines are assumed in future years; only the existing OSM topology is used. This is acceptable because the model constrains intra-GB power flows via boundary transfer capabilities rather than individual line ratings - **Interconnector onshoring locations**: The lat/lon of each interconnector's GB connection point is based on a best-guess interpretation of substation names in public project documentation - **Interconnector capacity plan**: The mapping of FES scenarios to specific projects and commissioning years is a best-guess derived by comparing cumulative interconnector capacities against the FES headline figures — see `our interconnector GitHub issue `_ for details .. _transmission-offshore-busmap: Offshore Bus Mapping -------------------- Offshore wind farms in the OSM network appear as stub buses outside the onshore regional boundaries. Without correction, network clustering can assign these stubs to the geographically nearest region, which may differ from the region they are electrically connected to — inadvertently creating spurious cross-region transmission lines. The ``identify_regions_for_offshore_buses`` rule resolves each offshore stub to its true onshore connection point and writes the result to ``resources/gb-model/custom_busmap.csv``, which is consumed by the PyPSA-Eur clustering step. .. seealso:: :doc:`data_cleaning` — detailed description of the offshore stub problem, the mapping algorithm, and illustrative figures. .. _transmission-availability: Transmission Availability ------------------------- Monthly availability fractions are derived separately for intra-GB lines and cross-border interconnectors. **Intra-GB (NGET, SPTL, SHETL)**: Zone-level unavailability fractions are averaged over the configured report years. The monthly mean is converted to an hourly ``0/1`` availability series by random sampling: for each month, a fraction of hours equal to the mean unavailability is drawn at random (using a fixed seed per zone for reproducibility) and marked as unavailable. This series is currently processed but not applied to individual line ratings; the intended use is to reduce boundary transfer capabilities rather than individual line ``s_nom`` values, consistent with how the model constrains intra-GB flows via boundary MW limits. **Cross-border interconnectors**: Unavailability is averaged across all projects and report years to produce a single monthly mean fraction (``sample_hourly: false``), applied directly as a ``p_nom_pu`` scalar rather than sampled hourly. .. seealso:: **Related Documentation**: - :doc:`system_dispatch_redispatch` - Network constraints and redispatch using transmission capacity - :doc:`system_generators` - Generation assets connected to the same AC buses - :ref:`model_config_gb` - Full configuration reference **External Resources**: - `OpenStreetMap / PyPSA-Eur OSM network `_ - Base grid topology - `OSM pre-built network dataset (Zenodo) `_ - gb-dispatch-model custom OSM archive (version 2026-02-20) - `NESO transmission availability reports `_ - Source of intra-GB and interconnector availability data - `ENTSO-E TYNDP `_ - Cross-border interconnector project reference