SaurEnergy Explains: How Grid-Forming Inverters Are Powering RE Grids

The accelerating shift to renewable energy is pushing power grids into uncharted territory. Traditional grids anchored by large spinning generators are giving way to systems dominated by inverter-based resources like solar, wind, and batteries.

Grid-forming inverters have emerged as a key enabling technology to maintain grid stability in this new paradigm. In this article, we explore a technical and market-oriented overview of grid-forming inverters and understand their important role in renewable integration to energy grids.

What are Grid-Forming Inverters and How Do They Work?

Grid-forming inverters (GFM) are advanced power electronic inverters capable of establishing and regulating an AC grid’s voltage and frequency, much like a traditional power plant generator. 

Unlike standard grid-following inverters that simply inject current into an existing grid waveform, a grid-forming inverter behaves as a controllable voltage source. It ‘forms’ the grid by setting a reference voltage and frequency, and automatically adjusts its output to balance changes in load or generation.

In essence, a GFM inverter can create a stable electrical island on its own or alongside other sources, making it invaluable for microgrids and black start scenarios. A black start is the process of restarting a power grid from a complete outage or blackout, without relying on external power sources. 

One key feature of grid-forming inverters is their ability to emulate the behavior of a synchronous machine through advanced control algorithms. Often referred to as virtual synchronous machines or virtual synchronous generators (VSG), the inverter dynamically responds to frequency deviations by drawing on stored energy, from a battery, to inject or absorb power. This phenomenon lets grid-forming inverters counter frequency drops and support voltage during disturbances.

Moreover, these modern inverters can also ride through faults and contribute to short-circuit current, within limits, supporting grid protection and recovery.

How are They Different from Existing Grid-Following Inverters?

Most of the inverters deployed today are grid-following (GFL). GFL types use phase-locked loops to synchronize with an existing grid sine wave and inject current accordingly, contrastingly opposite to grid-forming inverters which establish their own reference and can run autonomously.

It is by virtue of their different operating principles. Grid-forming inverters are voltage-source devices that create and regulate the grid’s AC voltage and frequency. By comparison, grid-following inverters are current-source devices that must sync to the grid’s voltage waveform and frequency. In short, A GFL inverter’s output is dictated by the grid’s conditions, whereas a GFM inverter dictates (or at least strongly influences) those conditions.

Another difference is in the black-start situation. Unlike GFM, GFL depends on a stable grid voltage/frequency reference and cannot operate if the grid is down or absent, limiting their use in standalone or outage scenarios.

The Indian Institute of Science (IISc) Bangalore highlights that when renewable penetration exceeds about 30 percent of grid capacity, the overall inertia of the system drops. Consequently, system stability can deteriorate due to the higher impedance and weaker control of distributed generation. A grid-forming inverter increases the system inertia, and thus supports stable operation even with high renewables and weak grid conditions.

However, the advanced control of GFM means that they come with greater complexity, cost, and slightly slower response than simpler grid-following designs. Further, integrating GFMs into existing grids poses challenges, like limited  short-circuit current capability and different fault response complicating protection systems. 

Industry standards and grid codes have also not caught up to define their required performance yet. By contrast, grid-following inverters are a mature, inexpensive technology with fast power-electronics response, and they avoid many of the new technical hurdles of GFM. 

Notably, currently battery energy storage systems (BESS) are the primary medium for grid-forming inverters, since adding this capability to batteries is seen as ‘low-hanging fruit’ for grid support. As per an Energy Systems Integration Group (ESIG) study, using GFM BESS instead of GFL BESS in a transmission system improves the hosting capacity for solar and wind generators.

Global Market Overview and Trends

Grid-forming inverters are rapidly gaining attention as the missing piece of the puzzle for resilient renewable grids that the world envisions. Though still an emerging market, growth is strong, estimated at around USD 0.7 billion in 2023 and poised to grow by roughly 8.2 percent annually through the current decade, as per a 2024 report by the Allied Market Research.

The start of the current decade saw the emergence of several major manufacturers offering grid-forming solutions. Major power electronics firms such as Huawei, Hitachi Energy, Siemens, General Electric, ABB, Delta Electronics, Enphase Energy, Eaton, Schneider Electric, and SMA Solar are among the notable providers of grid-forming inverter technology.

Battery storage integrators, like Tesla and Fluence, also offer grid-forming controls as a feature of their large-scale storage systems. 

Owing to their utility, experts suggest that grid-forming inverters will increasingly be included by default in new grid-scale batteries and renewable plants. One analysis envisions annual demand climbing into the tens of billions of dollars once grid-forming capabilities are adopted in 20-40 percent of new solar and wind installations and most large batteries.

Regional Status and Hotspots for Deployment

Regionally, Asia-Pacific is expected to be the largest and fastest-growing market for grid-forming inverters, reflecting enormous renewable energy expansion in countries like China and India. Europe and North America are also significant markets, especially as they retrofit stability services into grids retiring conventional plants.

Around the world, a few regions stand out as early adopters of grid-forming inverters due to high renewable penetration and proactive policy measures. Australia is at the forefront of grid-forming inverter deployment as the nation hosts the world’s largest transmission-connected GFM battery to date – a landmark 150 MW Hornsdale Power Reserve, also known as Tesla Big Battery in South Australia, has been operating in grid-forming mode using Tesla’s Virtual Machine Mode controls. The country is scaling up on the same with several new projects. 

The US is also moving forward with the new tech. The US DoE in 2021 launched the UNIFI Consortium, a USD 25 million program to advance universal interoperability of grid-forming inverters and develop industry standards. Regulatory moves include the Midcontinent Independent System Operator (MISO) proposing a framework requiring new battery storage projects to use grid-forming controls. 

On the deployment side, projects like the Wheatridge Renewable Energy Facility in Oregon, North America, are being planned to operate the battery with grid-forming inverters. 

In Europe as well the inverter technology is making progress. The UK has made headlines by deploying the first grid-forming battery systems to support national grid stability. The GFM batteries are part of a £323 million effort to replace the stability services once given by fossil-fueled plants. Others include Ireland and Denmark – testing grid-forming controls in wind farm and battery projects to address inertia shortfalls in their high-wind grids. 

Several EU Horizon research programs, like OSMOSE and MIGRATE, have focused on grid-forming converters. 

Status in Emerging Markets: India

The grid-forming inverters are also gaining traction in emerging economies – like India, South Africa, and parts of Latin America – where grids are expanding and renewable capacity is surging. As per the Allied Market Research study, the Asia-Pacific, including China, India, Australia, Southeast Asia, is expected to account for the largest share of grid-forming inverter adoption globally.

Thus far, most inverters in Indian projects are the conventional grid-following type, but stakeholders are beginning to recognize the need of GFM to preserve grid stability considering the higher penetrations of renewables. 

The National Smart Grid Mission (NSGM) hosted webinars and knowledge sessions in the past aimed at building awareness and technical capacity among grid operators. 

Some pilot projects are now being set out to incorporate the GFM inverters. For example, inverters in the Integrated Solar Energy Project in Modhera (India’s first solar-powered village) can operate in island mode to keep the village energized at night, effectively forming a mini-grid from stored solar energy. This demonstrates the real-world use of something closer to grid-forming, or at least grid-supporting, inverters. Overall, India is in the early exploratory phase with grid-forming inverters.