Modern grids rely on many different resources to stabilize the electricity they carry. But in simple terms, let's separate them into two main types: those that have "inertia" and those that don't.
Spinning resources like turbines and generators have inertia, meaning that they slow down and speed up in ways that directly interact with and improve the stability of the electrical system. Solar and wind power inverters lack inertia, and while they can be programmed or controlled to perform certain grid-balancing tasks, they just don't provide the same stability as spinning metal, magnets and wire.
This can be a significant problem for microgrids — self-contained systems of power generation, distribution and end loads. Microgrids tend to rely on diesel generators or small-scale turbines as their spinning resources, but would like to add more renewables to their systems.
For more information, please visit the Greentech Grid website.