IN Brief:
- Ordinance 464-A/2026/1 establishes frequency response, grid-forming and synthetic inertia requirements for qualifying electricity storage installations.
- The mandatory requirements cover transmission-connected and larger storage facilities, with different conditions for smaller installations.
- Portugal has launched separate auctions covering 750MVA of standalone storage connections and 300MVA for renewable generation with associated storage.
Portugal’s Ministry of Environment and Energy has introduced technical connection requirements for electricity storage installations, including grid-forming operation, synthetic inertia and response to changes in system frequency. Ordinance 464-A/2026/1 took effect on 23 October 2026, alongside a separate programme of competitive procedures for allocating electricity network capacity to new storage and renewable generation projects.
The regulations establish additional operating capabilities for batteries and other qualifying storage facilities connecting to Portugal’s public electricity network. They apply to connection applications submitted after the ordinance entered into force, while existing installations become subject to the requirements only under the circumstances specified in the legislation, including certain substantial modifications or equipment replacements.
Storage installations connected to the national transmission network must meet the grid-forming requirements regardless of their maximum power rating. The rules also establish mandatory capabilities for installations classified as Type D, including those rated at 45MW or more or connected at 110kV or above. Facilities in other categories face requirements determined by their rating, connection conditions and the relevant capacity reservation or authorisation documents.
Grid-forming control allows a power converter to establish and regulate electrical voltage and frequency characteristics rather than relying entirely on an existing network waveform. Conventional grid-following inverters measure the voltage and frequency at their connection point and synchronise their output to that reference. Grid-forming converters can contribute actively to maintaining those characteristics, provided the electrical equipment and its controls are designed to deliver the required response.
The distinction becomes increasingly important as electricity networks connect greater amounts of generation and storage through power electronic equipment. Conventional synchronous generators possess rotating mass that contributes mechanical inertia to the power system. Inverter-connected equipment behaves differently, making its programmed response and available energy central to the support it can provide during disturbances.
Portugal’s ordinance introduces synthetic inertia requirements under which qualifying storage installations must adjust active power in response to frequency deviations. A battery can increase export, reduce charging or absorb additional power according to the direction of the disturbance and its available operating capacity. The control system must coordinate those responses with the battery’s state of charge and the limits of its inverters.
The technical annexes address frequency excursions between 47Hz and 52.5Hz and rates of change of frequency of up to 2Hz per second. They also define parameters for the response of grid-forming equipment, including adjustable emulated inertia characteristics and damping of electrical oscillations. These requirements establish measurable operating behaviour for assessing converter performance during network studies and commissioning.
Grid-forming obligations vary with the installation category. Type C facilities, generally rated from 10MW to below 45MW, can face requirements specified through connection rights, permits or competitive procedures. Smaller installations are also subject to conditions appropriate to their classification, while facilities connected to distribution networks must support grid-following operation where required by the network operator.
The rules require installations of at least 1MW to possess specified technical capabilities for frequency containment and restoration reserves, together with voltage and reactive power control. Storage equipment also needs the monitoring and communications functions necessary to support remote supervision and operating instructions from the relevant network authority.
For batteries that are charging when system frequency falls, the ordinance establishes an automatic transition towards discharge for installations meeting the applicable threshold. The default underfrequency setting is 49.2Hz. The response can reduce the electrical demand imposed by the installation and, where available power permits, allow it to inject electricity into the network.
Those requirements affect both equipment specification and the operating strategy of a battery project. An installation providing frequency services needs suitable converter headroom and sufficient stored energy to sustain its contracted response. Commercial charging and discharging schedules must therefore be coordinated with the technical obligations established through the connection agreement.
The Portuguese requirements distinguish between storage technologies capable of supplying synthetic inertia and those that provide synchronous inertia through rotating machinery. The ordinance accommodates those different operating characteristics rather than imposing an identical inverter-based solution on every storage technology. The final compliance route depends on equipment classification and the technical conditions established for the connection.
Alongside the new technical rules, Portugal has opened two competitive procedures for electricity network capacity. The first covers up to 750MVA of connection capacity for standalone storage installations, while the second offers up to 300MVA for renewable generating plants with associated storage. The government confirmed the auctions publicly on 27 October, following the publication of the relevant orders on 22 October.
The standalone storage procedure requires projects to provide a minimum four-hour storage duration at their maximum injection power. Applicants must also satisfy conditions governing installed power and the network capacity allocated to them. Those provisions influence equipment sizing, because the required energy capacity increases with both the maximum discharge power and the specified operating duration.
For example, a battery designed to export 100MW continuously for four hours requires a nominal energy capacity of at least 400MWh before accounting for operational reserves and conversion losses. The auction’s 750MVA figure instead describes apparent power capacity available through the relevant connection arrangements. It is therefore separate from the aggregate battery energy capacity that successful projects may eventually install.
Projects combining renewable generation and storage face different eligibility and connection conditions. Their electrical design must accommodate the relationship between renewable output, storage charging and discharging, and the network’s permitted injection and import limits. Shared transformers and connection infrastructure can restrict simultaneous operating modes, requiring plant controllers to coordinate the relevant equipment.
The competitive procedures also include restrictions on network use in defined circumstances. Such restrictions affect how developers assess battery revenues, because energy trading and balancing services depend on the ability to import or export electricity at the required time. Project economics must account for the connection terms alongside battery efficiency, maintenance, operating costs and the expected market prices.
Portugal is expanding electricity storage as renewable generation contributes a growing share of national supply. Storage installations can absorb electricity when generation exceeds immediate demand and return energy during other periods, while suitably configured converters can provide faster responses to network disturbances. The new rules establish technical requirements intended to coordinate those capabilities with system security.
Developers seeking capacity through the auctions must satisfy the procedural requirements and subsequently complete the engineering and authorisation work for their chosen sites. Equipment selection, electrical studies, protection design and commissioning tests will determine whether individual installations comply with the connection rules.
The legislation is already in force, and the capacity allocation procedures have been launched. Their immediate effects will be reflected in the technical specifications submitted by prospective storage developers and the conditions imposed on successful applicants before construction and network connection proceed.
