Grid-Forming vs Grid-Following Inverters Explained

Grid-forming vs grid-following inverters: what's the difference?

Every inverter that connects a battery or a solar array to the grid has to answer one question: does it follow the grid, or does it help form it? That single distinction, grid-following versus grid-forming, sits at the center of how the modern grid will stay stable as it fills up with renewables and storage.

The terms sound similar, and both describe an inverter turning DC into AC. But they behave very differently, and the difference matters more every year. This guide explains both, plainly.

Start with what an inverter references

An inverter needs a reference for voltage and frequency, something that tells it what waveform to produce. Where that reference comes from is exactly what separates the two types.

A grid-following inverter takes its reference from the grid. A grid-forming inverter creates the reference itself. Everything else follows from that.

Grid-following inverters

A grid-following inverter, sometimes called grid-tied or grid-supporting, synchronises to an existing grid. It detects the grid's voltage and frequency and injects power in line with them. It is a follower by design: it needs the grid to already be there and stable, and it adjusts itself to match.

This is the traditional and still most common mode. It works very well when the grid is strong and present, which for decades it always was, held up by large spinning generators in conventional power plants. Most solar inverters installed to date are grid-following.

The limitation is simple. A grid-following inverter cannot run without a grid to follow. If the grid goes down, it goes down with it. And it does not, on its own, contribute to holding the grid's stability, it leans on the stability that is already there.

Grid-forming inverters

A grid-forming inverter can establish voltage and frequency by itself. Instead of needing a reference, it provides one. This lets it do things a grid-following inverter cannot.

It can form and hold up a microgrid with no connection to the main grid. It can ride through disturbances and actively support stability rather than just consuming it. And it can support black start, helping bring a system back to life after an outage without an external reference to lock onto. In effect, a grid-forming inverter can behave like the large generators that traditionally kept the grid stable, providing the strong voltage and frequency reference everything else follows.

This matters because those large spinning generators are slowly being displaced. As more of the grid becomes solar, wind, and battery storage, something has to provide the stability they used to. Grid-forming inverters are how power electronics take on that role.

Why this shift is happening now

For most of the grid's history, stability was a given. Conventional plants provided the inertia and the reference, and inverters could simply follow.

As renewable penetration rises, that assumption breaks down. A grid with very high renewable content and few spinning generators has less natural stability, and at times weaker reference points for followers to lock onto. If every inverter is only a follower, there is a real question of who holds the grid up. Grid-forming capability answers it, which is why grid codes and system operators are increasingly asking for it, especially on storage projects.

Where the PCS comes in

In a storage system, this behavior lives in the Power Conversion System. A capable PCS is not locked into one mode. It supports grid-following operation for normal grid-tied duty and grid-forming operation for microgrids, black start, and stability support, and it meets the smart-inverter functions and grid codes such as IEEE 1547 that define how it must behave.

If you want the broader picture of how a PCS converts and controls power in a storage or solar-plus-storage system, we cover it in what is a Power Conversion System. Grid-forming versus grid-following is really about which control mode that PCS is running in.

A simple way to hold the difference

A grid-following inverter is a passenger. It needs the grid to drive, and it rides along, contributing power but relying on the grid for stability.

A grid-forming inverter can be the driver. It can establish the reference, hold up an islanded system, and provide the stability others follow.

Modern power systems need both, and increasingly they need inverters that can do either depending on what the grid requires at that moment.

The takeaway

Grid-following inverters synchronise to an existing grid and inject power in line with it, which works well when the grid is strong. Grid-forming inverters create their own voltage and frequency reference, so they can support microgrids, ride through disturbances, and enable black start. As renewables and storage displace conventional generation, grid-forming capability moves from a nice-to-have to a requirement, and it is one of the most important jobs a modern PCS performs.