Tracking Great Britain's Changing Electricity Grid

Ten years ago, coal regularly supplied more than a third of Great Britain’s electricity. By the autumn of 2024, Ratcliffe-on-Soar — the country’s last coal-fired power station — closed its doors for good. In that same decade, offshore and onshore wind grew from a rounding error into the single largest source of generation over whole winter weeks.

When I started building the GB Grid tracker and bot network, the goal was straightforward: report what is powering the grid every half-hour settlement period without burying the numbers in dashboards that take ten seconds to load. Getting the numbers right, however, means dealing with a quirk of how Britain meters its electricity.

The transmission vs. distribution blind spot

If you query Elexon’s Balancing Mechanism Reporting Service (BMRS) for instantaneous fuel outturn (FUELINST), you get a clean breakdown of generation by fuel code every five minutes. Look at it at 13:00 on a sunny June afternoon, though, and something looks wrong: solar is nowhere to be seen.

Fuel Category	BMRS Code	Metering Level	Included in FUELINST?
Combined Cycle Gas	CCGT	Transmission (400/275 kV)	Yes
Nuclear	NUCLEAR	Transmission	Yes
Transmission Wind	WIND	Transmission	Yes (~75% of GB wind)
Interconnectors	INT*	Transmission	Yes (9 cables)
Embedded Solar PV	—	Distribution (≤132 kV)	No (appears as negative demand)
Embedded Wind	—	Distribution (≤132 kV)	No

Because almost all solar farms and rooftop arrays in Great Britain connect to local distribution networks rather than the high-voltage national transmission system, the transmission system operator only sees them indirectly as a drop in national demand (INDO). If you compute fuel shares using FUELINST alone on a summer afternoon, you undercount renewables and overstate gas and nuclear shares by 15 to 25 percentage points.

Reconciling BMRS outturn with Sheffield Solar PV_Live

To report true supply-side shares, the /gb-grid ingestion worker merges two upstream feeds at +7 and +37 minutes past each hour:

1. Elexon Insights (FUELINST) for transmission-metered BMUs and interconnectors.
2. University of Sheffield PV_Live alongside NESO’s embedded wind estimates for distribution-connected generation.

from dataclasses import dataclass
from datetime import date
import httpx

BMRS_OUTTURN_URL = "https://data.elexon.co.uk/bmrs/api/v1/generation/outturn/summary"
PVLIVE_URL = "https://api.pvlive.uk/pvlive/api/v4/gsp/0"

@dataclass(frozen=True)
class SettlementSnapshot:
    settlement_date: date
    period: int          # 1..48 (or 1..50 on autumn clock change)
    by_fuel_mw: dict[str, float]

    @property
    def total_supply_mw(self) -> float:
        # Exclude pumped-storage pumping (negative) and net exports from supply denominator
        return sum(mw for code, mw in self.by_fuel_mw.items() if mw > 0)

    def share_pct(self, fuel: str) -> float:
        total = self.total_supply_mw
        return round((max(0.0, self.by_fuel_mw.get(fuel, 0.0)) / total) * 100.0, 1) if total else 0.0


def fetch_merged_period(client: httpx.Client, settlement_date: date, period: int) -> SettlementSnapshot:
    bmrs = client.get(
        BMRS_OUTTURN_URL,
        params={"settlementDate": settlement_date.isoformat(), "settlementPeriod": period},
        timeout=10.0,
    ).raise_for_status().json()

    fuels: dict[str, float] = {row["fuelType"]: float(row["generation"]) for row in bmrs.get("data", [])}

    # Layer in national embedded solar PV (GSP 0 = national total)
    pv = client.get(PVLIVE_URL, params={"extra_fields": "installedcapacity_mwp"}, timeout=10.0).json()
    if pv_rows := pv.get("data"):
        fuels["SOLAR"] = float(pv_rows[0][2] or 0.0)

    return SettlementSnapshot(settlement_date=settlement_date, period=period, by_fuel_mw=fuels)

Treating FUELINST as total generation is the most common bug in amateur UK energy trackers. On a sunny bank holiday, embedded solar alone can exceed 11 GW — more than every nuclear and biomass unit combined.

Interconnectors as a two-way valve

The other structural change over the past five years has been interconnector capacity. With North Sea Link (INTNSL, 1.4 GW to Norway), ElecLink (INTELEC, 1.0 GW through the Channel Tunnel), IFA2 (INTIFA2, 1.0 GW to France), and Viking Link (INTVKL, 1.4 GW to Denmark) all online, Great Britain can now import or export well over 8 GW across nine subsea cables.

When Scottish and North Sea wind output exceeds north-to-south transmission bottlenecks (B6 boundary constraints), Great Britain frequently flips from net importer to net exporter for hours at a time — pushing surplus power into continental Europe and Norwegian hydro reservoirs while paying domestic wind farms to turn down north of the bottleneck.

Following the live feeds

If you want the numbers in your feed without checking a dashboard, the GB Grid documentation page lists all nine automated accounts (@GBGrid, @GBGridWind, @GBGridSolar, @GBGridNuclear, @GBGridImports, @GBGridCoal, @GBGridGas, @GBGridHydro, and @GBGridBiomass), their exact cron schedules, and the threshold rules that trigger record alerts.