Spain's RT3 cost ×10 since 2020 — and what changed after the blackout

Updated 2026-05-21 · Thanks to Sergio Bertolín for the expert feedback: we initially called RT3 "tertiary reserve" — RT3 is actually the consumer-side cost of technical constraints in the day-ahead market (REE redispatching the OMIE clearing to keep synchronous units online for security). All data, ratios, and the renewable correlation stand; the mechanism is now precisely identified. Both posts have been updated, with details corroborated by PwC's February 2026 report on REE's post-blackout Operación Reforzada.

Two data pieces went live on the Iberian power system, both built on public regulator data (ESIOS) plus our internal ClickHouse mirror. Same question from two angles: who pays for integrating variable generation, and how is that bill changing?

• RT3 (technical constraints in the day-ahead market), the hidden cost of integrating renewables in Spain's grid: ×10 since 2020. 148 months of data, Pearson +0.76 against the share of PV + wind generation (controlled for OMIE wholesale price). The structural break is RT3, not the gas-cap mechanism.
• 12 months after the Iberian blackout (2025-04-28): the system absorbs the same renewable share, but the cost of technical constraints has multiplied ×2.5 and negative-price hours ×4.4 — driven by REE's Operación Reforzada. Same physics, different bill.

Both pieces below — read whichever angle interests you first.

Both pieces above were built by talking to a ClickHouse mirror of ESIOS data with AI — same workflow, two different angles, in hours rather than weeks. Two ways to get there:

• Use the same data we used. datons-esios gives you AI-assisted, chat-driven access to the full Iberian electricity dataset (markets, ancillary services, settlements, generation mix). Self-serve, ready today.
• Run it on your own infrastructure. We're now building the same kind of AI-assisted analytics layer inside client infrastructure — your data, your security perimeter, your business questions. If you have a database that should be answering more questions than it currently does, let's talk.