Spain’s National Commission for Markets and Competition (CNMC) has formally approved the Especificaciones de Detalle (EEDD), a new set of technical and methodological criteria that will determine grid-access capacity for electricity demand connected to the national transmission network. The measure, framed under Article 18 and Annex III of Circular 1/2024, applies both to new grid-access applications and to requests seeking to modify existing permits.
These rules have significant implications for demand-side energy storage, covering standalone battery energy storage systems (BESS) as well as units hybridised with generation assets. The regulation explicitly defines the types of access capacity that can be granted: firm, flexible or self-consumption linked to on-site generation.
“The access capacity resulting from the application of these specifications will be firm capacity for consumers,” the resolution explains. It also clarifies that flexible access capacity will be available for storage facilities, an adjustment intended to reflect changing consumption patterns and the increasing role of active users in the electricity system.
A major milestone under the new regime will be the first publication of demand access-capacity maps by the national transmission system operator Red Eléctrica de España (REE) on 2 February 2026, fulfilling the requirements established in the third clause of the resolution. From that date onwards, grid-access evaluations will be conducted using a methodology that integrates nodal, zonal and both static and dynamic system-behaviour considerations.
The renewable energy sector has long called for more integrated planning between Spain’s transmission and distribution networks to anticipate real demand growth and avoid congestion. Industry stakeholders have also warned that five-year planning cycles exclude urgent industrial projects and that network and storage deployment is already lagging behind territorial needs.
The scope of the EEDD is broad. It applies to consumers directly connected to the transmission grid, as well as to demand connected through distribution networks that require an “acceptability report” due to their influence on the transmission system. Grid operators, distribution network owners and consumers under self-consumption regimes are also included under the new framework.
From a technical standpoint, the regulation establishes three main evaluation criteria:
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Short-circuit strength (Weighted Short Circuit Ratio, WSCR),
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Static behaviour, and
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Dynamic behaviour,
each applicable depending on the type and configuration of the installation. Notably, Power Electronics Interface Consumption (CEP) facilities will face short-circuit constraints due to their impact on system stability.
The reform also introduces the concept of Common Influence Zones, which will be used to allocate shared capacity in cases where multiple installations significantly affect the same network node. These zones are determined through tools such as power-flow sensitivity matrices and statistical models applied to the reference planning scenario.
Connection points will no longer depend solely on the applicant’s preference. Under Operating Procedure 13.1, REE will retain the authority to designate both the substation and the exact position of the connection, ensuring technical viability and minimising system-wide costs.
One of the key obligations is the monthly publication of updated information on available access capacity at transmission nodes, within the first five days of each month. These publications must include reference values at transmission-distribution boundary points and follow reporting criteria previously communicated to the CNMC.
The document also establishes transitional measures and detailed timelines. Within two months, REE must convene a working group with technology providers to assess potential regulatory integration of grid-forming (GFM) technologies applied to Máquinas de Potencia Electrónica (MPE) and CEP systems. Within six months, a joint proposal with distribution system operators will be required to improve information exchange on granted permits—crucial for coordinating mutually influential nodes.
Another requirement mandates that by 15 November each year, REE must submit a report to the CNMC justifying the use of the 98th percentile (rather than the 95th) for static-criteria access-capacity calculations for storage installations, with the possibility of modification from 2027 onwards.
The resolution will enter into force the day after publication in Spain’s Official State Gazette (BOE), with specific exceptions such as Section 4.3 of Annex 1, which will only apply once the October 2026 capacity maps are released. Until then, current study scenarios will remain in use. The document has already been forwarded to the Ministry for Ecological Transition and Demographic Challenge (MITECO), REE and distribution companies for formal implementation.
With this regulatory step, the CNMC closes a process initiated in 2024, which included working groups and consultations with Spain’s electricity sector. The first capacity map, scheduled for February 2026, is expected to mark a turning point for demand access to the transmission grid and could have a direct impact on investment decisions in storage, self-consumption and industrial infrastructure projects.
