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.
But the more they add, the more they rely on the uncertain ups and downs of wind and sun-generated power, all coming from inverters that lack the inertial stability that comes from spinning generators. This can quickly add up to system-wide instability that can force generators to ramp up and down wildly, push grid protection gear into states it’s not meant to handle, or force the wind and solar to shut off altogether.
Swiss grid giant ABB believes it has an answer to this challenge in PowerStore, a grid stabilizing generator that combines the inertial properties of a flywheel, the power management functions of advanced inverters, and the software to make it all work together. Think of it as an entire grid’s worth of generators, power electronics and control systems, shrunk to the size of a cargo container, that can push the practical penetration of renewable power from around 15 percent to 20 percent, to as high as 100 percent.
That sounds like a bold claim, but according to Brad Luyster, vice president and general manager of ABB’s microgrid business, that’s exactly what many of the systems using PowerStore are handling today. Of course, it’s rare to see sun and wind power completely supply a microgrid’s power needs, so those systems fluctuate between 100 percent and as low as 40 percent renewable energy through the course of a day, or a year.
Through it all, “PowerStore is the voltage and frequency supplier,” he said, keeping supporting diesel generators from “hunting” up and down, or grid protection gear from tripping on and off, in a vain attempt to balance out fluctuations.
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