Why the Future of Renewable Integration Depends on Choosing the Right Technology

As power systems embrace more solar, wind, and storage, the choice of inverter technology becomes pivotal for grid stability. The traditional grid-following (GFL) inverters can only operate when a strong grid voltage and frequency already exist, whereas grid-forming (GFM) inverters actively establish and regulate voltage and frequency. Industry experts now assert that achieving very high penetrations of renewable energy cost-effectively will require widespread use of grid-forming inverters. In essence, GFM technology allows inverter-based resources to behave much like conventional generators, ensuring the lights stay on even as synchronous machines retire. Below we explore the fundamental differences, real-world impacts, advantages, industry requirements, implementation challenges, and strategic implications of adopting GFM inverters for a renewable-powered future.

The Fundamental Difference

The core distinction between grid-forming and grid-following inverters lies in how they reference and control the grid voltage and frequency. GFM inverters act as voltage sources, creating a stable reference waveform internally, whereas GFL inverters behave as current sources that wait for an external reference from the grid. In practice, a grid-forming inverter sets its own AC voltage magnitude and frequency (often using droop control or virtual oscillator techniques) and then feeds power into the system based on that reference. A grid-following inverter, by contrast, uses a phase-locked loop (PLL) to measure the grid’s existing voltage phase and frequency and then injects current in sync with that signal. This fundamental control difference has broad implications: a GFM unit can run independently (even forming an islanded microgrid) since it doesn’t need an external signal, whereas a GFL unit cannot function without a live grid – it will simply shut down if the grid reference disappears. In summary, grid-forming devices create the grid conditions, while grid-following devices rely on them. This single difference in who “leads” and who “follows” drives all other contrasts in performance and stability.

Real-World Consequences

The choice between GFM and GFL inverters has tangible consequences for power system stability and reliability. Consider a wildfire or storm knocks out a transmission line, isolating a section of the grid. If that section has grid-forming inverters, they will maintain frequency and voltage in the islanded area until the grid can be reconnected. But if the same area relied only on grid-following inverters, all would likely trip offline as soon as the external grid signal vanished, causing blackouts.

On a larger scale, as more synchronous generators retire, power systems lose the inertia and damping those spinning machines provided. High renewable penetrations dominated by GFL inverters have experienced issues like rapid frequency swings or even widespread outages. Without grid-forming capability, operators must resort to expensive alternatives like synchronous condensers to stabilize frequency and voltage. The evidence is mounting: relying solely on grid-following inverters in high-renewable grids leads to instability, whereas grid-forming inverters provide the safety net that keeps the lights on.

The GFM Advantage

Grid-forming inverters offer several critical advantages for high renewable penetration grids:

• GFM inverters mimic traditional generator inertia, adjusting output to counter sudden imbalances and providing immediate frequency stabilization through droop control. A grid-forming unit actively arrests frequency changes, whereas a grid-following unit simply tracks frequency drift without correcting it.
• Because they regulate voltage as a source, GFM inverters inherently support voltage stability and can share reactive power loads amongst themselves, similar to multiple generators. Grid-following inverters can only provide limited reactive support and cannot take charge of system voltage during disturbances.
• During grid faults, grid-forming inverters continue operating based on their internal reference, supporting the grid through the fault. Grid-following inverters often lose phase-lock during voltage dips and may cease output when support is most needed.
• GFM inverters excel in weak grid conditions by establishing themselves as a stiff voltage source, damping oscillations and preventing voltage/frequency swings. Multiple GFMs can run in parallel to form entirely inverter-based islanded grids. GFL units cannot sustain islands or stabilize weak grids without external help.
• Grid-forming inverters can start up a dead grid and establish frequency/voltage from scratch, invaluable for system restoration and microgrid applications. Grid-following inverters cannot perform black start operations.

GFM inverters bring to renewable resources the same stabilizing traits that synchronous generators provide: inertia, voltage regulation, fault tolerance, and independent operation capability.

Industry Recognition and Requirements

Regulators and grid operators around the world are recognizing the value of grid-forming technology and are beginning to require its capabilities in new installations. For instance, multiple countries and regions have updated grid codes or standards to incorporate GFM performance: Germany will require inertia response (a service only inverter-based sources with grid-forming controls can provide) starting in 2026, the UK’s Grid Code now includes specific provisions for grid-forming inverter behavior, and Australia has introduced detailed performance standards and testing frameworks for GFM inverters. Even in North America, which historically used GFL inverters for renewables, progress is underway.In fact, compliance with these modern grid codes and standards is becoming a “frontline design decision,” effectively pushing manufacturers and project developers toward adopting grid-forming controls to meet the criteria.

One clear area where this shift manifests is in model quality testing (MQT) and validation requirements for inverter-based resources. Traditionally, a grid-following inverter’s model was validated with a limited set of standard tests – for example, confirming that its behavior during voltage steps, frequency steps, and fault ride-through events in simulation matches reality. These tests assumed the inverter would be responding to grid events (since a GFL inverter doesn’t set the grid conditions). Grid-forming inverters, however, require a more extensive testing regime because they are expected to actively shape grid conditions. Industry working groups have defined additional model validation tests specifically for GFM systems beyond those used for GFL. For example, in ERCOT’s recent grid-forming battery test framework, engineers introduced new scenarios to ensure the models accurately capture GFM behavior:

• Islanding (Loss of Last Machine): Testing that a GFM inverter can stably carry an islanded grid when the last synchronous generator is tripped, maintaining frequency on its own.
• RoCoF Response: Applying a rapid change in frequency (Rate of Change of Frequency) to verify the inverter’s controls respond with appropriate inertia/frequency support.
• Weak-Grid and Phase Angle Step Tests: Stressing the inverter with a sudden phase angle jump or a drop in short-circuit strength (SCR step-down, possibly with added series capacitance) to observe its stability under extreme grid impedance conditions.
• Energy/Headroom Response: Ensuring the inverter’s energy source and control (e.g. battery state-of-charge management) can deliver the needed surge or damping during disturbances – for instance, a sudden load change or generation surge.
• Frequency Scan and Damping: Sweeping through frequencies to check how the GFM unit interacts with system resonances, confirming that it provides damping across a range of sub-synchronous and harmonic frequencies.

Some of these tests are run as pass/fail criteria (to confirm the inverter meets minimum performance, like maintaining stability), while others are informational to characterize performance limits. This is a step change from GFL inverter testing – grid-forming models must prove their capability to form and stabilize a grid, not just ride through disturbances.

Furthermore, entities like WECC have had to develop entirely new simulation models because existing generic inverter models (built around GFL behavior) “could not represent grid-forming inverters,” underlining that industry-wide modeling practices are evolving to accommodate GFM technology. In summary, GFM inverters face higher scrutiny in testing: they are held to all the usual ride-through and control standards of GFL units, plus additional requirements to demonstrate they can manage grid voltage/frequency on their own. This ensures that as GFM deployments grow, their behavior in the grid is well-understood and reliable under a wide range of conditions.

Implementation Challenges

Despite the clear technical and reliability benefits of grid-forming inverters, there are still significant challenges to their widespread implementation. From an engineering perspective, the single biggest hurdle is achieving stable operation when many GFM inverters run in parallel on the grid. Unlike GFL units that defer to a central grid reference, each GFM inverter asserts its own voltage source; if not carefully coordinated, multiple independent voltage sources can interact and even fight each other. Coordinating these devices without instability is complex – for instance, slight differences in their control settings or sensing can cause power oscillations between inverters. Manufacturers have had to develop advanced schemes (like virtual impedance, adaptive droop, and synchronization controls) to allow multiple grid-forming inverters to share load and maintain lock-step without oscillation. This challenge of tuning and managing parallel operation is frequently cited by experts: essentially, ensuring dozens or hundreds of GFMs behave cooperatively as a coherent grid is non-trivial.

Another technical hurdle closely related to the above is meeting grid protection and fault-handling requirements with inverter-based resources. Traditional grids assume generators contribute large fault currents; GFMs, being power electronics, have limited overcurrent capability. To truly replace synchronous machines, grid-forming inverters must be engineered to supply sufficient short-circuit current (or alternative fault signals) and handle overloads for brief periods. This often necessitates hardware improvements (e.g., more robust semiconductors or intelligent fault control strategies) and careful interplay with existing protection relays. In short, the hardware and control complexity of GFMs is higher – they need fast, precise control and sometimes extra capacity to perform like a virtual generator. This added complexity translates to heavier validation effort (as discussed) and sometimes higher costs or design constraints (such as oversizing inverters to provide headroom for inertia/fault response).

Finally, it’s worth noting that operational experience with large-scale GFM deployment is still limited. Grid operators and engineers are climbing a learning curve in understanding how best to integrate these devices (e.g., setting standards for droop settings, forming fallback strategies if multiple GFMs interact, etc.). This is more of a soft challenge, but it underpins the technical issues: with more real-world projects and testing, many of these coordination and control challenges are being actively addressed. In summary, the main technical barrier to widespread GFM adoption is ensuring stability and compatibility at scale – particularly, making sure that many grid-forming inverters can work together and with legacy systems seamlessly. Overcoming this will involve continued R&D in control algorithms, protective schemes, and standardized protocols for GFM behavior.

Strategic Implications

Embracing grid-forming inverter technology carries significant strategic implications for the energy industry and the transition to renewables. For grid operators and planners, it means rethinking grid design and interconnection requirements. The trend is clear: grid-forming capability is poised to become the default expectation for new renewable and storage projects as the need for grid stability becomes paramount. Many system operators are already signaling this shift by updating grid codes (as noted above) and procurement criteria. Those utilities and regions that proactively adopt GFM in their networks will likely find it easier to integrate higher levels of renewables without reliability problems, whereas those that delay may face increasing instability or be forced into expensive stop-gap measures (like retrofitting synchronous condensers or keeping gas plants on standby purely for inertia support).

For renewable project developers and technology manufacturers, the rise of GFM inverters is both an opportunity and a mandate. Companies that invest in grid-forming capabilities (hardware and software) will gain a competitive edge as the market pivots to this advanced functionality. Indeed, industry leaders are already showcasing successful large-scale GFM deployments – for example, massive battery-PV hybrid plants operating in grid-forming mode to provide reliable off-grid power in remote areas. These early projects demonstrate that GFM technology is not just a theoretical concept but a practical solution ready for prime time. Manufacturers like Sungrow, SMA, Tesla, and others are actively refining their grid-forming offerings, knowing that future contracts (especially in grids nearing 100% renewable targets) may demand nothing less.

On the policy and planning side, the strategic importance of GFM inverters is tied to national and global clean energy goals. Studies and consortia funded by government agencies (such as the U.S. DOE’s UNIFI Consortium) underscore that reaching high renewable penetration while maintaining grid reliability hinges on deploying grid-forming controls at scale. Policymakers are starting to incorporate these requirements into long-term resource planning – for instance, by incentivizing or mandating that a certain percentage of new inverter-based resources have grid-forming capabilities, or by creating market mechanisms to reward services like inertia and fast frequency response that GFMs provide. In essence, grid-forming inverters are becoming a strategic asset: they enable a cleaner grid without sacrificing stability, thus smoothing the path toward decarbonization. Conversely, failure to develop and adopt these technologies could bottleneck the energy transition, as grids might otherwise become too unstable with large shares of passive, grid-following resources.

Choosing the right inverter technology is far more than a technical detail – it is a foundational strategic decision for the future grid. Grid-forming inverter technology offers a way to rewrite the rules of renewable integration, allowing solar, wind, and battery systems to step into the role once played by conventional power plants in keeping the electrical system stable. The industry momentum and research investments in GFM indicate a broad consensus: to achieve a reliable, 100% renewable power system, grid-forming inverters will be indispensable. Stakeholders who recognize and act on this now will lead the way in the energy transition, setting the stage for power systems that are not only sustainable but also resilient and secure.