Voltage at the edge: what Spain's blackout means for Europe's energy transition
As the world accelerates its transition to renewable energy, the resilience and adaptability of national power systems are being tested like never before. The Iberian Peninsula blackout in April 2025 serves as a stark reminder of the critical importance of robust voltage management and regulatory frameworks in supporting grid stability to enable secure system operation with relevant shares of non-dispatchable renewable sources. The causes and consequences of the blackout are still being investigated in detail, however information and analysis released so far reveal much about the evolving role of renewables in grid operations across Europe.
Evolution of the black out (as reported by ENTSO-E)
At the time of the blackout, most of Spain’s demand was being met by solar PV generation. At 12:32pm on 28 April, a voltage increase was seen across the transmission network due to the following factors:
- Approximately at 12:32 pm, more than 500 MW of distributed (wind/solar) generation is lost via disconnections in distribution networks.
- At 12:32:57, 12:33:16 and 12:33:17, three major generation loss events occur in quick succession.
- In the following 3 seconds, a sharp rise in voltage (southern Spain into Portugal) occurs causing generators to disconnect in cascade; frequency drops and the synchronism with mainland Continental Europe is lost.
- Between 12:33:19-12:33:22 automatic defence measures activated (load shedding, system defence plans) but were insufficient to prevent collapse.
- By 12:33:24, the links with France and Morocco have tripped and there is a full system collapse; the blackout is effective in the Iberian Peninsula.
The exact reasons for many of these disconnections remain unidentified and while multiple factors contributed to the blackout, the prevailing theme was a lack of effective voltage management. This raises questions about system monitoring, observability, operational planning and grid code compliance.
Impact on Spain’s voltage management regulation
Prior to the blackout, Spain’s voltage management framework had remained largely unchanged for 25 years with only conventional generators mandated to provide dynamic voltage control. Renewable energy plants were not required to do so and, when they did, could only offer limited static voltage control by operating at a fixed power factor. This meant reactive power support was only available when active power was being exported, which did not always align with real-time grid needs.
Modern inverter-based renewable energy generators can provide voltage management beyond operating at fixed power factors. Other countries in Europe have already taken advantage of this:
- Germany requires renewable energy systems to provide automatic voltage control based on predefined reactive power response curves;
- Great Britain mandates automatic voltage regulation for new inverter-based generation (such as renewables) exceeding 1 MW; and,
- In Australia automatic/dynamic voltage control is mandatory at all scales – even for small- to mid-sized distributed energy connections.
Following the blackout, amendments were made to the TSO Technical Operating Procedures requiring all plants – including asynchronous renewables – to participate in reactive power provision for voltage regulation through at least static voltage control. Oversight of voltage management to ensure compliance has also been strengthened alongside the introduction of penalties for non-compliance.
Further regulatory proposals by Spain’s National Commission on Markets and Competition (CNMC, independent authority in charge of competition and regulatory matters) including establishing a market mechanism for contracting reactive power capacity to support voltage management are under parliamentary discussion.
Impact on wider European voltage management regulation
ENTSO-E is currently undertaking a detailed third-party investigation of the blackout event with the final report of causes expected to be available by October 2025. Following this, a further report on recommendations to prevent such events will be produced for the European Commission and member states.
As part of its investigations, ENTSO-E is considering:
- enhancing voltage control management procedures and capabilities of all active parties in the electricity system to prevent major voltage-related incidents in the future; and,
- assessing how the system defence plans can better protect the European power system against this new type of phenomena.
Future of renewable energy in Spain
The recent blackout has underlined the urgency of strengthening Spain’s regulatory framework, particularly around the monitoring and oversight of voltage control. Although initial steps have been taken, a central element will be providing the CNMC with stronger powers to ensure that technical requirements are not only clearly defined in the grid codes, but effectively delivered in practice. This means coupling compliance monitoring with clear incentives (both bonus and malus), so that the obligation to provide system services such as voltage support is linked to sustainable revenue streams and penalties for non-compliance. Only by aligning technical mandates with economic signals will the system ensure the long-term reliability of a grid increasingly dominated by inverter-based resources.
From a market design perspective, the blackout has also reopened the debate on the adequacy of current planning procedures and governance structures. Stronger, more independent planning – less exposed to short-term political or corporate influence – may require a rethinking of which entity leads system planning and, ultimately, of the TSO model itself. A clearer separation between transmission ownership and system operation could improve neutrality, enhance transparency and allow planning decisions to reflect the true system needs of a rapidly changing energy mix. Such reforms would also bring Spain closer to the best practices observed in other jurisdictions.
For renewable energy developers, the evolution of ancillary services and the emergence of locational services represent both a challenge and an opportunity. Projects will increasingly be required to incorporate automatic and dynamic voltage control capabilities at the design stage, raising technical complexity and costs. Yet, this also opens the door to new sources of revenue, as renewable energy assets can monetise their flexibility and grid-support features in evolving market mechanisms. Ensuring investor confidence will depend on providing clear, bankable frameworks for rates of return which reward system-friendly projects rather than treating compliance purely as a sunk cost.
For storage developers, the blackout highlights an even clearer path forward. Battery projects – whether standalone or hybridised with RES plants – are uniquely positioned to stack revenues by providing fast, automated voltage support in addition to energy arbitrage and reserve products. The current and ongoing market reforms have unlocked this potential by creating specific voltage-related services that recognise the technical capabilities of BESS and reward optimal siting alongside renewables.
Addressing the blackout’s roots in poor distribution network observability and limited TSO-DSO interaction will be critical. Modern, automated distribution systems and tighter transmission–distribution integration must be supported by regulation that enables distribution companies to invest – with a fair rate of return – in the digitalisation and monitoring infrastructure required to keep Spain’s grid secure.
