As governments, investors and utilities race to decarbonize electricity systems, an uncomfortable tension has emerged: how do we replace fossil-fueled, synchronous generators, the traditional anchors of grid stability, with variable renewables, while keeping the lights on? The technical and policy answers are no longer academic.
Recent grid failures, policy moves and engineering breakthroughs show the energy transition’s promise and its engineering constraints, and they point to one obvious truth: reliability must be engineered into the transition, not assumed.
The backdrop: rapid change, rising electrification
Renewable capacity has been added at an extraordinary pace worldwide. The International Energy Agency’s forecasts show a strong near-term rise in renewables and electrification, shifting the generation mix and increasing electricity’s role across transport, heating and industry. That creates both opportunities, lower operating costs and falling emissions, and operational dilemma for system operators.
What reliability means today (and why it’s harder)
Traditional thermal plants (coal, gas, large hydro) are synchronous machines: when they spin they naturally provide inertia and clear frequency behaviour that stabilises voltage and frequency during sudden disturbances. Wind and solar plants, by contrast, connect through power electronics (inverters) and are inherently low-inertia.
As the share of inverter-based resources grows, system inertia drops, making grids more sensitive to fast imbalances and more prone to oscillations and voltage issues unless engineered otherwise. Recent technical literature and reviews characterise this as a central technical challenge of low-carbon grids.
The risk is not that renewables “cause blackouts” per se, but that grids designed around synchronous behaviour must be rethought. The Iberian blackout of April 28, 2025, which cascaded quickly after a voltage surge and planning shortfalls, is a stark reminder that planning, protection settings and operational practices must evolve as the resource mix does. Spanish and Portuguese authorities found the outage rooted in technical and planning failings, not an attack, and urged stronger resilience and system planning.
Engineering responses: tools to restore what was lost — in new ways
Engineers are not helpless. Several mature and emerging tools can recreate the stabilisingfunctions of conventional plants, while letting the power come from renewables.
• Grid-forming inverters (GFMIs). Unlike conventional grid-following inverters, grid-forming control lets inverter-based resources set voltage and frequency references, emulating inertia and damping. Research and pilot projects demonstrate that GFMIs can substantially improve stability in low-inertia systems and are central to plans to run high-renewable grids reliably.
• Battery energy storage systems (BESS). Fast-responding batteries can arrest frequency drops within milliseconds, provide synthetic inertia, and smooth daily variability. Deployment has accelerated rapidly in recent years and is now one of the most effective short-term stability tools.
• Virtual inertia and advanced controls. Utilities are deploying software and control architectures that synthesize inertia from inverter fleets, use fast grid telemetry to orchestrate responses, and coordinate distributed resources. These ‘virtual inertia’ approaches are increasingly the subject of academic and industry optimisation frameworks.
• Grid reinforcements and transmission build-out. More and better transmission reduces the need for local, costly reserves by sharing variability over larger geographic footprints. Policy decisions to accelerate grid-permitting and cross-border planning can unlock stranded renewable output and reduce curtailment. The European Commission’s recent moves to fast-track grid projects reflects this reality.
• Operational reform: market and scheduling changes. Faster markets, longer-horizon system planning, stronger contingency reserves and demand-side flexibility (including smart charging of EVs and industrial demand response) all give operators more levers to match supply and demand in real time. The IEA and other authorities emphasise flexibility as a coequal pillar alongside generation.
Policy reactions: speed without shortcuts
Policymakers are waking up to the need for accelerated grid works and new rules. The EU’s December 2025 proposals to shorten permit times and centralise planning show political will to fix bottlenecks in transmission and interconnection that otherwise throttle renewables and hamper reliability. But fast permits must be paired with robust environmental assessments and cybersecurity checks to avoid new risks.
At the same time, countries facing unusual supply-demand conditions, for instance, France’s late-2025 reports of local oversupply and weak electrification growth, reveal that system balance is not a one-size-fits-all problem. Some places will need faster electrification, industrial off-take or export infrastructure; others will need to scale back some generation at certain times or invest in long-duration storage. These are engineering and economic trade-offs that policymakers must manage with data and iterative planning.
The middle path: pragmatic transition engineering
The most resilient road to decarbonisation is pragmatic and layered:
1. Design for Decarbonisation and Stability. New renewable projects should be evaluated not only for energy output and cost but for their contributions to system stability (e.g., co-located storage, grid-forming capability, or firming power contracts).
2. Retain or repurpose firm capacity during the transition. Some synchronous capacity (nuclear, hydro, dispatchable gas with carbon management) will be needed as a bridge while inverter and storage fleets scale and grid reinforcements complete.
3. Prioritise flexibility. Invest in BESS, demand response, smart EV charging, and longer-duration storage (pumped hydro, hydrogen, thermal storage) to manage multi-day variability and seasonal imbalances.
4. Upgrade operations and protection. Modern protection schemes, real-time network management systems and coordinated control allow faster, safer handling of disturbances, reducing the chance that a local event cascades into a regional blackout.
5. Regulatory reform and planning. Accelerated permitting, coordinated cross-border planning, and market reforms for faster dispatch are essential, but must preserve environmental standards and cyber-resilience.
What engineers — and the public — should expect next
Engineering the energy transition is not merely swapping assets; it is rewriting the grid’s operating logic. Expect more investments in converter technology, national and regional planning reforms, and a surge in storage and grid-forming deployments. Expect also tighter integration between power systems and other sectors, transport, industry and hydrogen, so electricity can both decarbonise those sectors and absorb their loads flexibly.
Crucially, the path to net zero must carry reliability along with it. Recent incidents, from the Iberian blackout to operational stresses in multiple systems, show that lapses in planning, protection and operational reform can turn a technical vulnerability into a social and economic crisis. That does not argue for delaying decarbonisation; it argues for doing it with engineering discipline, deliberate sequencing and investment in the tools that recreate the stabilisingfunctions we have depended upon for a century.
Conclusion: engineering the bargain
Energy transition and energy reliability are not zero-sum. With intentional engineering, grid-forming inverters, fast storage, stronger transmission, smarter operations and sensible policy, grids can become cleaner and more reliable than the systems they replace. The bargain is explicit and technical: societies must invest now in the control systems, storage, transmission and market reforms that will let renewables carry the load securely. Done well, the transition is not an arrival at a fragile new normal, but a redesign of electricity systems that is cleaner, smarter and more robust.
