Market Overview
Frequency Response
GB frequency response is procured through three dynamic services, each split into High (discharge — activated when frequency falls below 50 Hz) and Low (charge — activated when frequency rises above 50 Hz) auctions.
| Service | Frequency band | Role |
|---|---|---|
| DC – Dynamic Containment | ±0.2–0.5 Hz | Arrests large deviations within ~1 second |
| DR – Dynamic Regulation | ±0.015–0.2 Hz | Maintains frequency in normal operation |
| DM – Dynamic Moderation | ±0.1–0.5 Hz | Moderates frequency during stressed conditions |
Auctions run daily for each EFA block (six 4-hour windows covering the full day). The clearing price is the marginal accepted bid for that block and service.
EFA block timings
EFA Block 1 spans midnight (23:00 the previous calendar day to 03:00). All times are local GB time.
Clearing prices — 28-day rolling average by service
Individual auction results are first averaged to a daily figure per service, then smoothed with a 28-day rolling window, so the trend for each of the six services is readable without daily noise obscuring the signal.
Key takeaways — clearing price trends
- 2022 peak then sharp compression. DCH clearing prices peaked at £15–20/MW/h in 2022 as NESO expanded DC procurement ahead of renewable growth. From late 2022 a rapid wave of new GB BESS capacity entered the frequency response markets, outpacing NESO's procurement volumes and driving prices steeply lower across all services.
- Discharge (High) services generally clear above charge (Low) services. Fleet-wide charge headroom tends to be more available than discharge headroom — particularly during high-wind periods — so Low-side auctions typically clear lower.
- DRH and DRL behave differently from DC and DM. DR's sustained 60-minute delivery requirement couples the two sides operationally, which is why the DRL spread sometimes inverts relative to DCL and DML.
Price distribution
DCH shows the widest spread of outcomes, reflecting its role as the primary fast-discharge service and its early-market dominance at elevated prices. Evening blocks (EFA 5–6, 15:00–23:00) attract higher premia as demand peaks and wind output often eases; the overnight block (EFA 1) is typically cheapest to procure.
Summary statistics
High vs Low spread
Each service runs two separate auctions: High (falling frequency — BESS discharges) and Low (rising frequency — BESS charges). Clearing prices differ because available discharge and charge headroom across the fleet is rarely symmetric.
Spread = H clearing price − L clearing price. Positive means discharge capacity was scarcer; negative means charge capacity was scarcer.
Daily average H − L spread over time
Spread distribution by market
Average spread by EFA block
DC shows the widest range of spread outcomes — its higher median reflects the relative scarcity of fast-discharge capacity. DR sits firmly negative across both charts, confirming the structural inversion described above. DM occupies the middle ground. Evening blocks (EFA 5–6) show the most pronounced spreads, as demand peaks and the balance between available charge and discharge headroom is tightest.
H − L spread heatmap: EFA block × month
Each cell is the average H − L spread for that market, EFA block and calendar month. Red = discharge capacity scarcer (H > L); blue = charge capacity scarcer (L > H).
Grid & settlement prices
System Buy Price (SBP) and System Sell Price (SSP) are the cash-out prices used to settle imbalance in the GB Balancing Mechanism. Parties that are short pay the SBP; parties that are long receive the SSP. The gap between them incentivises self-balancing rather than relying on the system operator.
Wholesale price spread
Daily peak-to-trough APXMIDP spread — the raw arbitrage opportunity available to a battery on any given day, before efficiency losses and cycling cost.
Thin line is the daily spread; heavy line is a 28-day rolling average.
Generation mix
GB generation by fuel group. The mix matters for BESS because it shapes the underlying risk of frequency deviation: high wind with low demand pushes frequency high (requiring charge / Low-side response), while low wind with high demand can cause dips (requiring discharge / High-side response).
14-day rolling mean, smoothing day-to-day noise while still resolving seasonal swings. Click legend entries to isolate a fuel group.