Energy curtailment

EU law treats curtailment as one kind of redispatching. Regulation (EU) 2019/943, Article 2(26), defines redispatching as a measure, including curtailment, activated by transmission or distribution system operators that alters generation, load or both in order to change physical flows, relieve congestion or otherwise ensure system security. Article 13 sets the order of preference. Redispatching should be market-based and paid. Non-market-based redispatching is allowed only in listed cases, for example when no market-based alternative exists or all market resources have been used. Renewable generators may be curtailed this way only if no other alternative exists, and self-generated electricity that is not fed into the grid should not be curtailed unless no other solution resolves a network security issue. Article 13(7) requires the operator that orders non-market-based redispatching to pay financial compensation, unless the plant accepted a non-firm connection agreement, one with no guarantee of firm delivery of energy.

In practice an engineer meets curtailment in four forms, and only the first is what the regulation calls redispatching. A system operator orders a plant to reduce output or switch off. A connection agreement caps how much power the site may export. A zero-export rule forbids export altogether, so PV output is limited to what the site consumes and the battery absorbs. And an owner or trader curtails voluntarily when the price of exported energy drops to zero or below.

Article 13(4) of the regulation obliges operators to report redispatching every year, and URE publishes the summary. For 2024 URE reported that, on PSE's orders, non-market redispatching of PV plants reduced generation by 595,168.4 MWh to balance the national power system and by 2,095.7 MWh because of transmission constraints. For wind the figures were 118,047.6 MWh and 7,027.7 MWh. Distribution operators curtailed a further 24,121.1 MWh of PV on their own orders, and only 3 of the 188 distribution operators did so.

URE describes non-market redispatching of renewables for balancing as a last-resort action. PSE first limits generating units on the balancing market, uses pumped storage, redispatches thermal units outside the balancing market and redispatches across borders. Only then does it order renewable plants to reduce output, directly for plants connected to the transmission grid and through distribution operators for the rest. The same orders can also switch off an energy storage unit or change the power it takes or delivers.

For an EMS curtailment is a constraint that arrives from several directions at once and has to win over everything except safety. Requirements worth specifying:

• Signals have a written priority. Safety limits, grid operator orders, connection export caps, peak shaving and trading will all act on the same inverters and battery. The system needs a fixed order and a screen that shows which rule is limiting output right now.
• Each controller reacts to its own trigger. A safety controller that throttles the battery whenever any limit is active will cost energy for no reason.
• The limit is enforced at the connection point. The EMS reads the grid meter, compares export with the limit and adjusts the inverters in a closed loop. The loop needs a margin for inverter response time, and a safe fallback, such as zero export, when the meter stops responding.
• Surplus goes into the battery before PV is cut. With a battery on site, the EMS can charge it with energy that may not be exported, which needs headroom in the battery's state of charge before the expected curtailment hours.
• Forecasts and reports know about curtailment. A production forecast for hours with export blocked should be capped at consumption plus battery charging, or the app will show energy that was never produced.
• Every event leaves evidence. Compensation and disputes depend on the start, end and value of the limit, the power the plant could have produced and the power it actually produced.

The EMS we built for Skyfri takes signals from the distribution system operator that limit the export of a factory's energy to the grid for grid safety. By October 2024 it included export curtailment on grid operator request, zero-export and zero PV export algorithms, and a maximum site load limiter, tested on site with the grid operator.

For Global Green's battery storage sites we built separate controllers in 2026:

• the distribution operator's export limit,
• the distribution operator's battery limit and direct battery commands,
• PV export limitation and grid export limitation,
• a safety curtailment controller.

Testing showed that the safety controller throttled the battery regardless of what had triggered it. We fixed it in September 2026.

In Zeronest's home EMS, anti-reflux (blocking export to the grid) is one of the manual battery modes, and the automatic algorithm switches to it when the price for exported energy is zero or negative. In 2026 we corrected the production forecast so that, in hours with anti-reflux planned, it shows no more than consumption plus battery charging.