Grid-forming inverter
Also known as: grid-forming inverters, GFM inverter
A grid-forming inverter is power electronics that lets batteries, solar, and wind actively set the grid's voltage and frequency, instead of simply following signals from big spinning generators.
That ability matters as coal and gas plants retire, because their heavy rotating machines naturally stabilized the grid. While grid-forming inverters sound like an engineering detail, they may decide how high a share of renewables a grid can safely run on.
Grid-forming inverter, explained at three levels
At home
Think of the grid as a choir. Big power plants used to be the lead singers, holding a steady pitch that everyone else followed. Solar panels and batteries were backup singers who could only copy. A grid-forming inverter turns them into lead singers too: it sets its own steady rhythm, so the choir stays in tune even after the old power plants retire.
At work
A grid-forming inverter is power electronics that lets batteries, solar, and wind set the grid's voltage and frequency rather than just following them. That matters as coal and gas plants retire, because their spinning generators used to provide that stability for free. Grid-forming capability lets renewable and battery projects provide stability services that utilities once bought only from conventional plants.
At home
Solar panels and batteries make direct current (DC), but the grid runs on alternating current (AC), which swings back and forth 60 times a second in North America. An inverter converts DC to AC by switching electronics on and off very rapidly. A grid-following inverter measures the grid's existing rhythm and copies it. A grid-forming inverter generates its own steady rhythm, like a metronome, so other equipment can lock onto it.
At work
Grid-forming inverters behave like a voltage source, much as a generator does, rather than a current source that needs an existing grid to follow. Control methods include droop control and virtual synchronous machine designs that mimic a generator's physics. That lets them provide synthetic inertia, fast frequency response, voltage support, and black start, restarting a grid after a blackout. They are essential for microgrids without generators and increasingly valuable on large grids with high renewable shares.
At home
When a big power plant trips, frequency starts to fall. Spinning generators resist that drop automatically, because their heavy rotating mass stores energy and releases it instantly, which is called inertia. Grid-forming inverters have no such mass, so they imitate the effect with fast measurement and software that injects power within milliseconds. In my view, the remarkable part is that code can now do a job that used to need thousands of tonnes of spinning steel.
At work
Challenges include limited fault current, since inverters typically supply only slightly more than their rated current during a fault, compared with several times rated current from generators, which affects protection relays. Many inverters close together can interact and oscillate, and performance requirements are still being standardized. Grid operators are updating interconnection rules such as IEEE 2800, and Australia's market operator has published a voluntary grid-forming specification. Compensation for stability services remains unsettled in most markets.
Real-world examples
At home
Nadia lives in a remote Yukon community whose microgrid added a large battery. She learned the battery's grid-forming inverter allowed the town to occasionally run on solar and storage alone, with the diesel generators switched off.
At work
Jerome is a transmission planner at a Canadian grid operator. As gas plants retire, his studies showed stability problems in one region. Requiring grid-forming capability on new battery projects proved cheaper than building synchronous condensers.
How it compares
| feature | Grid-forming inverter | Grid-following inverter |
|---|---|---|
| Behaviour | Sets voltage and frequency | Follows the existing grid signal |
| Can run an island alone | Yes | No |
| Stability services | Inertia-like response, black start | Limited |
| Prevalence | Growing | Most installed inverters |
Grid-forming inverters lead the grid. Grid-following inverters follow it.
For analysts
Specifying grid-forming capability on new battery projects is a small cost that may become a requirement later. I'd ask for it in procurement now, rather than retrofitting when grid rules change.
History & origin
Most solar and battery inverters installed in the 2000s and 2010s were 'grid-following': they synchronized to the grid's existing waveform and couldn't keep it stable alone. Island grids, such as those in Hawaii and remote Australia, needed alternatives early because they had few large generators. South Australia, with very high solar and wind shares, became a testing ground; batteries there, including the Hornsdale Power Reserve, were upgraded for grid-forming services in the early 2020s. In 2023, North American reliability bodies and researchers began publishing grid-forming specifications, and grid operators in Australia, the UK, and elsewhere began requiring or rewarding the capability. In my opinion, grid-forming inverters are the quiet enabler of the renewable transition.