How does MIBEL shape each battery dispatch decision? MIBEL, the Mercado Iberico de Electricidade, is the integrated electricity market for Portugal and Spain. For battery operators on the Iberian Peninsula, it provides the main market context for dispatch. When Pollen changes a battery's charge or discharge schedule, it is reacting to prices produced by MIBEL's clearing process. Knowing how that process works helps explain the system's decisions.
This article examines MIBEL from a battery operator's viewpoint: the day-ahead market's output, the operation of intraday sessions, the conditions that separate Portuguese and Spanish prices, and the practical implications for automated dispatch.
The day-ahead market: the planning foundation
OMIE, the Iberian Energy Market Operator, administers MIBEL's day-ahead market. Every day, generators, traders, and large consumers place bids and offers for each of the 24 delivery hours on the following day. The submission window ends at noon CET. OMIE then runs its market-clearing algorithm and publishes results at approximately 13:00 CET.
The result is 24 hourly marginal clearing prices for the next day, stated in EUR per MWh. Battery operators use these day-ahead prices to plan overnight charging. When Pollen establishes initial charge targets for your battery each afternoon, the MIBEL day-ahead prices released by OMIE are its main input.
MIBEL is integrated into the European price-coupling mechanism, which connects day-ahead prices across multiple markets through implicit cross-border capacity allocation. When interconnector capacity between the Iberian Peninsula and France is sufficient, MIBEL prices tend to converge toward French prices during low-renewable periods. During high-solar midday hours, Iberian prices typically diverge downward as Iberian solar generation saturates local demand without enough interconnector capacity to export the surplus.
The intraday market: six sessions that revise the forecast
MIBEL's intraday design differs fundamentally from continuous intraday trading on markets such as EPEX SPOT. Instead of permitting bilateral trades nearly up to real time, MIBEL conducts six separate intraday auction sessions during every 24-hour cycle.
Every session has its own gate closure time, delivery window, and covered delivery hours. Session 1 opens in the late afternoon of day D and covers hours beginning in session D+1 through that day's end. Sessions 2 through 6 progressively approach real time and cover shorter horizons for hours not yet delivered. Session 6 runs in the early hours of the following morning, when only a few delivery hours remain.
The auction process is consistent across sessions: bids and offers are accepted, the session clears, and marginal prices for its delivery hours are published. Those intraday prices may differ substantially from the previous afternoon's day-ahead prices. Changes in demand, renewable output, or grid conditions after day-ahead gate closure are reflected in the intraday result.
Why the session structure matters for dispatch timing
For a battery dispatch system, every session close is a price-discovery event that can call for a position change. The difference between day-ahead prices and intraday clearing prices is often material, especially when solar or wind output changes unexpectedly.
Take a winter morning in Portugal. The day-ahead auction expected moderate afternoon wind and priced those delivery hours at 80 EUR/MWh. Overnight, actual wind output rises significantly across the Iberian Peninsula. Session 2, which includes the afternoon hours, clears at 55 EUR/MWh. A battery planned for an 80 EUR/MWh afternoon discharge using only day-ahead prices now holds a less attractive position.
An automated dispatch system tracking MIBEL revises its dispatch parameters whenever a session clears. If the result shows materially lower prices during the battery's target hours, it can discharge earlier in a currently higher-priced window, retain SoC for a later window, or change the overnight recharging target SoC. Manual dispatch updated only once per day from day-ahead prices cannot react to these intraday changes.
Portugal versus Spain: when the single price zone splits
In normal grid conditions, MIBEL treats Portugal and Spain as one price zone. A battery in Lisbon and one in Madrid face the same day-ahead and intraday clearing prices. This is the usual state.
Congestion creates the exception. If transmission capacity between Portugal and Spain cannot support price equalization, OMIE splits the price area and the Portuguese price separates from the Spanish price. This commonly happens when Portugal has surplus renewable generation, especially wind from the northwestern generation belt, that Spanish demand cannot absorb because of interconnection limits. Portugal's price is then usually lower.
During congestion, a site's price area determines the price feed used for dispatch. A site in Portugal must use the Portuguese price zone. Feeding Spanish prices to a Portuguese asset would base dispatch on a market clearing price the asset is not actually exposed to. Pollen stores each site's market zone explicitly and directs it to the appropriate price feed.
Imbalance settlement and why dispatch accuracy matters
Operators participating directly in MIBEL or through a BRP arrangement face imbalance settlement. If actual generation or consumption differs from the market schedule, the difference is settled at a price that can be substantially different from the scheduled price. Scarcity events can produce imbalance prices well above clearing prices, while surplus events can push them well below.
Dispatch accuracy determines part of a battery operator's imbalance exposure. If a battery scheduled to discharge 10 kWh in a delivery period actually supplies 7 kWh because of an SoC calculation error, it is short by 3 kWh. That 3 kWh is settled at the applicable imbalance price, which may be unfavorable. Accurate SoC tracking and realistic delivery schedules reduce this exposure.
A less visible but economically significant role of automated dispatch is controlling the difference between scheduled and actual delivery. Manual dispatch more often leads to optimistic schedules, with commitments based on nominal battery capacity instead of current SoC and realistic round-trip efficiency for the cycle.
Reading Pollen's dispatch logs through the MIBEL lens
When Pollen settlement logs show a charge or discharge command at an unexpected time, the usual reason is that an MIBEL intraday session cleared differently from the day-ahead forecast. Session 3, covering late-afternoon delivery hours, may clear 30 EUR/MWh above day-ahead prices, causing the system to move discharge forward and capture that window before it closes. Session 4, covering early evening, may then clear lower, supporting the earlier dispatch decision.
The session design is not complexity for its own sake. It gives the market progressively better price discovery as delivery nears. A dispatch system participating in all six sessions, instead of treating day-ahead prices as final, tracks market conditions more closely.
