Elexon Imbalance Prices - GB System Price Export & Revisions

Export Great Britain's electricity imbalance settlement prices from Elexon BMRS: system sell and buy price, net imbalance volume, and every specified DISEBSP field. Backfill dates for a battery optimisation backtest, then schedule a recent-date watch to capture value revisions and their previous values. No API key or proxy is required.

Input

An empty input {} exports the last three complete settlement days, calculated at run time in Europe/London. It produces data on weekends too. To backfill a month:

{
    "startDate": "2026-09-01",
    "endDate": "2026-09-30",
    "mode": "all",
    "watchName": "battery-backtest",
    "maxRows": 20000,
    "maxDays": 400
}

Input	Default	Meaning
startDate	UK today minus 3 days	Inclusive settlement date, YYYY-MM-DD.
endDate	UK yesterday	Inclusive settlement date. Future dates are clipped to UK today with a summary note.
mode	all	all exports all periods; changes exports only new or value-revised periods compared with this watch.
watchName	default	Persistent watch name, 1–128 characters. Reuse it to compare later runs.
maxRows	20000	Delivered row cap; 0 means unlimited.
maxDays	400	Reject ranges longer than this many inclusive requested days, before clipping. Can be reduced, never increased above 400.

Dates must be valid and startDate must be on or before endDate. Omit both dates to keep a scheduled task's window moving automatically; fixed dates stay fixed.

Output

One billable default-dataset row represents one settlement period. JSON, CSV and Excel exports are available through Apify. All dates and period numbers refer to the UK settlement day; all timestamps are exact UTC ISO strings. A normal day has 48 half-hour periods, clocks forward has 46 and clocks back has 50. A BST day's UTC start is 23:00 the preceding date.

These selected fields are from a real 14 October 2026 response (full exports contain all fields listed below):

{
    "settlementDate": "2026-10-14",
    "settlementPeriod": 1,
    "startTime": "2026-10-13T23:00:00.000Z",
    "endTime": "2026-10-13T23:30:00.000Z",
    "periodsInDay": 48,
    "createdDateTime": "2026-10-14T23:44:36.000Z",
    "systemSellPrice": 161.7,
    "systemBuyPrice": 161.7,
    "netImbalanceVolume": -32.18260232638889,
    "publication": "republished",
    "changeType": "new",
    "changedFields": [],
    "previous": null
}

Every row includes:

• Identifiers and timing: settlementDate, settlementPeriod, startTime, endTime, periodsInDay, createdDateTime, retrievedAt.
• Prices and volume: systemSellPrice, systemBuyPrice, netImbalanceVolume, reserveScarcityPrice, sellPriceAdjustment, buyPriceAdjustment, replacementPrice, replacementPriceReferenceVolume.
• Source flags: bsadDefaulted, priceDerivationCode.
• Accepted and adjustment volumes: totalAcceptedOfferVolume, totalAcceptedBidVolume, totalAdjustmentSellVolume, totalAdjustmentBuyVolume, totalSystemTaggedAcceptedOfferVolume, totalSystemTaggedAcceptedBidVolume, totalSystemTaggedAdjustmentSellVolume, totalSystemTaggedAdjustmentBuyVolume.
• Revision information: publication, changeType, changedFields, previous.

Source nulls remain null and numeric precision is preserved. Prices are GBP/MWh; volumes are MWh. Unknown additional API fields are accepted but not exported. Invalid envelopes, missing fields, wrong types, duplicate periods or incorrect UTC starts make that date an error rather than delivering questionable rows.

Re-publication watches

Elexon initially publishes a period roughly 48 minutes after it starts and re-publishes it roughly a day later. The endpoint returns only the latest publication. publication is derived from timing: republished means createdDateTime is more than 12 hours after endTime; otherwise it is first. This is a heuristic, not a flag supplied by Elexon.

changeType compares every exported DISEBSP value field (prices, volumes, flags and derivation code) with the watch snapshot. Settlement identifiers and UTC bounds are validated separately, and are not value fields:

• new: the watch has never delivered this period.
• revised: any value differs, even if createdDateTime is unchanged. changedFields lists those field names.
• republished: all values are equal, but createdDateTime differs. changedFields is empty.
• unchanged: values and timestamp match. changedFields is empty and previous is null.

For revised and republished rows, previous contains the old createdDateTime, systemSellPrice, systemBuyPrice, netImbalanceVolume and the old value of every field in changedFields. It is null for new and unchanged rows.

The real 15 October 2026 period-21 pair illustrates why this matters: the first publication timestamp was 2026-10-15T09:48:33Z and the re-publication timestamp was 2026-10-16T09:44:26Z, with every other source field identical. This is republished, not revised.

The first changes run delivers every available period as new. This baseline is billed per row. Later runs deliver and bill only new and revised periods. Timestamp-only re-publications deliver no row: their new timestamps refresh the watch state for free and are counted in the free summary. all delivers every period, computes all four change types against existing state and updates snapshots for delivered rows. Repeated all runs bill every delivered row again.

For a nightly recent-day watch, schedule this input:

{ "mode": "changes", "watchName": "battery-nightly" }

State is stored in a persistent named key-value store, elexon-watch- plus the first 32 hex characters of the SHA-256 of the exact watch name. SUMMARY.watchStore identifies it. The version-2 state stores every exported DISEBSP value field plus createdDateTime, retaining only the latest 60 distinct seen settlement dates. Older version-1 state is treated as absent, so its next changes run delivers a fresh billed baseline. Re-reading older discarded dates starts a new baseline for those dates. Use one run per watch at a time; concurrent runs can overwrite each other's state. To reset, choose a new watch name or delete its STATE record. Each Apify account owns its stores.

New or revised values advance state only after their rows are confirmed stored. maxRows, a spending cap or failed delivery leaves unreported new/revised periods eligible for the next run. In changes mode, equal-value timestamp refreshes can advance state without a row, including when delivery is capped, because no value change needs reporting. If data storage succeeds but state persistence fails, a retry may deliver and bill those rows again. Missing publications between runs cannot be recovered because Elexon serves only its latest snapshot.

Free coverage summary and errors

The default key-value store's SUMMARY record is free and never appears in the default dataset. It contains the requested and effective date range, one entry per fetched date with expected/received periods, rows delivered, rowsCutByMaxRows, rowsCutBySpendingLimit, countsByChangeType for delivered rows, observedCountsByChangeType for all fetched periods before caps or filtering, notes, attribution and the licence link. Thus a timestamp-only re-publication in changes mode increments observedCountsByChangeType.republished but has no delivered row or item charge.

Date status is complete, partial (today, or a closed day with missing periods), empty (no published data), or error with a reason. Future dates beyond the clipped range are not fetched. A request that exhausts retries, HTTP 400 or malformed body affects only that date; the actor continues and fails after saving the summary only if every fetched date errored. Storage and state failures abort the run. A wholly future range succeeds with zero rows and a clipping note.

There is one sequential request per settlement date, at least 500 ms apart. HTTP 429, 5xx and transport failures get up to four retries, exponential backoff and Retry-After. Today's coverage is provisional and yesterday can still be re-published. Repeat recent days rather than assuming a closed settlement day is final.

Pricing

$0.001 per delivered settlement-period row, plus $0.005 per actor start. Both are Apify's built-in events: apify-default-dataset-item and apify-actor-start. The platform bills the start event even when a run delivers no rows. A typical three-day default run delivers 144 rows: $0.149 including the start. Clock-change windows differ by two rows. The free summary has no dataset-item charge. Console monetization settings must be configured before publishing; the repository pricing file alone does not configure billing.

Licence and attribution

Contains BMRS data © Elexon Limited copyright and database right 2026.

BMRS data copyright licence. Commercial use is allowed. Keep this attribution and licence link whenever you republish the data, including in sub-licences and any further sub-licences. Do not imply Elexon endorses you or this actor. Each run's summary includes the attribution with the current year and the licence URL.

For support, open an issue on the actor's Apify Store page with the run ID, dates and affected periods. Do not post credentials. Public task and Store listing are pending publishing; current implementation and verification details are in the repository.