Eli5: how will a power grid that is mostly powered by many non synchronous renewable generators (solar and wind etc) remain stable, when the stability of the grid is currently reliant on the collective inertia of the large scale base load generators of fossil fuel and nuclear power plants?
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It won’t. Switching transistors inside inverters can’t respond to large load fluctuations fast enough. Small fluctuations are ok, but most solar and battery systems are on small grids, or small portions of large grids, and the load changes they see are frequently too large to support.
Traditional rotating power generators, like turbines in dams and coal/nuclear plants, provide stored energy that loads can extract for brief periods of time, giving controllers time to adjust fuel and/or voltage set points. The inertia dampens “real” loads, while the electromagnetic field stored in the air gap of the generator dampens “reactive” loads. Solar and battery inverters have neither, so they do a very poor job supporting large changes in load. The result is frequent overload conditions and the renewables open their breakers, making them useless.
Inverters use silicone based diodes and transistors to convert DC to AC. All of the current must pass through these components, but they have a fundamental limit to their current carrying capacity. That limit is for lower than copper or steel, and the end result is a severely restricted ability to provide fault duty currents. When a large load turns on, the electrical components inside have to energize before work can be done. This is called in rush, and it’s much higher in reactive loads. A rotating genset made of copper and iron can provide 5-8 times the nominal nameplate capacity as fault duty for very brief time periods. An inverter might provide 1.2 times nominal. From personal empirical observation, a 5hp industrial motor powering a large fan consumes ~5kW and ~2kVAR at steady state, so a 5-10kVA genset can run it all day long. That same fan pulls ~30kVAR at start up, which requires ~100kVA of generation to support, which is far more than the 5-10kVA genset can handle. It would require 5-10 times that much generation in the form of battery inverters to support the same in rush.
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