The grid-forming inverter market may soon inflect from $1bn to $15-20bn pa, to underpin most grid-scale batteries, and 20-40% of incremental solar and wind. This 11-page report finds that grid-forming inverters cost c$100/kW more than grid-following inverters, which is inflationary, but integrate more renewables, raise resiliency and efficiency?
The output of a solar module, a lithium ion battery, or a rectified wind turbine generator comes in the form of Direct Current, i.e., a steady flow of charge.
However, power is transmitted and mostly consumed as Alternating Current, a smooth sine wave of rising and falling voltage and current. This makes it easier to alter voltages in transformers and drive motors that are 40% of global electricity.
Inverters are used to convert DC to AC. In fact, there are two ways of synthesizing an AC waveform from a DC generation source: using pulse-width modulation or by stacking transistors, as outlined on pages 2-3.
But how do the inverters know what waveform to synthesize, i.e., at what frequency, phase angle and in synchrony with the rest of the grid? Historically the answer has almost entirely been via grid-following inverters, as described on page 4.
The issue that arises for energy systems with high penetrations of inverter-based resources – wind, solar and batteries – is that grids become unstable once grid-following inverters start providing around 60-70% of the instantaneous power, as described on pages 5-6.
Grid-forming inverters are the solution to enable stable grids with higher instantaneous shares of inverter-based generation. We outline how they work, and what they cost, on pages 6-7.
Other advantages of grid-forming inverters appear in small grids, in island grids, or when preventing the inefficient operation of rotating generators at low loads, which in turn can amplify fueling costs and CO2 intensity factors by 2-4x, per pages 8-9.
Our estimates of market sizing for grid-forming inverters are outlined on page 10 and a short screen of leading grid-forming inverter companies is on page 11, alongside some conclusions.