On 23 October, a Portuguese ministerial order took effect that reads like a technical annex but behaves like a market filter. Decree 464-A/2026/1 requires battery storage connected to the national transmission grid — and any storage plant rated 45MW or above — to operate in grid-forming mode and supply synthetic inertia. For developers, the question is no longer whether a battery can earn money from arbitrage. It is whether the battery is allowed onto the grid at all.

What the ordinance actually demands

The text extends the EU network code for generating units to storage, and it applies across the full operating envelope: discharging, charging, and even the auxiliary loads a plant draws while idle. Plants of 500kW and above must switch automatically from charging to discharging when frequency falls below a preset threshold, 49.2Hz by default. Plants of 1MW and above must be technically capable of providing frequency containment and restoration reserves plus voltage and reactive power control, and must give system operators real-time monitoring and remote control.

The technical annex, drawn from a joint report by ENTSO-E, SolarPower Europe and partner bodies, sets the numbers that matter: synthetic inertia across a frequency band of 47.0–52.5Hz and rates of change up to 2Hz per second; an emulated mechanical starting time adjustable between 1 and 20 seconds, defaulting to 12; a damping ratio of at least 10% for power oscillations between 0.1Hz and 10Hz; and load changes ramped over ten minutes unless reserves are being activated. Pumped hydro and other technologies that already supply synchronous inertia are exempt.

Why Lisbon moved before Brussels

Portugal drew 80% of its electricity from renewables in January this year and has a draft national storage strategy targeting 6.9GW by 2030. Its battery fleet, by contrast, stood at roughly 20MW at the end of 2025 — a base small enough that rules can be imposed before the market scales, rather than retrofitted onto it. In January 2025 the government awarded €100 million to 43 projects totalling about 500MW.

The near-total Iberian blackout of spring 2025 supplied the political urgency. A grid running on inverter-based generation with vanishing synchronous inertia is a different operational problem, and Portugal chose to write the answer into connection rules while Brussels is still revising its generator code. The same logic explains the timing of the market opening: two auctions launched on 23 October offer 750MVA of connection capacity for standalone batteries and 300MVA for storage co-located with renewables. Standalone projects must deliver at least four hours at full injection power, and in exchange the transmission operator may curtail charging or discharging for up to 500 full-power hours a year — a cap that can eat a meaningful share of day-ahead trading revenue.

The private side is moving on the same schedule. Sonnedix commissioned two solar-plus-storage plants in Portugal, pairing just under 70MWp of PV with 140.5MWh of batteries. On the equipment side, SMA chose All-Energy Australia in Melbourne to launch a DC-coupled grid-forming solar-plus-storage product aimed at Germany, Australia and the UK.

What it means for anyone buying storage

• Grid-forming is a delivery capability, not a tick-box. The hardware premium is modest; the real cost sits in simulation, modelling, commissioning tests, and the argument over responsibility when a test fails. Ask for a certification or third-party test report accepted in the target market, not a feature list.
• Put grid compliance in the contract. Frequency bands, damping ratios, ramp rates and inertia response curves are hard to renegotiate once a connection permit references them. Specify who runs the compliance test, who pays for remediation, and what happens to the schedule if the plant fails.
• Make sure the EMS can hear the operator. The ordinance lets the system operator issue power-limiting instructions during congestion or emergencies, and requires remote control. An EMS that cannot ingest and execute a curtailment or charge-limiting signal will leak revenue for the life of the asset.

The wider signal is hard to miss. Discussions at ENTSO-E point toward grid-forming as a baseline requirement for large-scale storage across Europe, and Germany's inertia market is already opening. For suppliers targeting Europe, Australia, the Middle East or Africa, grid-forming capability is converging on the same status as UL 9540A fire testing: a precondition for bidding, not a point of negotiation.