The struggle to maintain the system grid is a constant battle for Independent System Operators. California is a fitting example of how this works.
On April 24, 2021 at 2:30 pm, California renewables produced 94% of their electricity demand for 4 seconds. On the surface one might say this is moving in the right direction; however, there is more to the story.
At that exact moment, natural gas plants were generating 3,442 MW and Diablo Canyon nuclear plant, 1,144 MW. This generation, coupled with the renewable generation, was a problem for grid operators of too much supply. Too much supply can overload the grid and result in equipment connected to the grid, like your refrigerator or air conditioning unit, overheating or burning up.
To prevent that, grid operators CAISO needed to reduce supply. They could shut down solar or wind operations, or export the excess energy to other utilities. Any of these is an additional cost to the customer unless another utility needs that excess energy. On this day, Arizona, Nevada, and Oregon did not need the power and the least costly option was to export 2,489 MW to them, but at a cost to the customer, a process called negative pricing.
On the other hand, at the peak time around 8pm, wind and hydro were the only significant renewable sources available, as solar was zero output. Therefore, CAISO imported more than 25% of their electricity demand from other states, once again at the expense of the California customers. Natural gas generation was limited in power that could be provided and in the future, this source may not be available at all based on recent actions taken in California to eliminate natural gas generation. Utility-scale battery storage is inefficient at 5,000 MW, ~20% of peak demand, and this energy source is in reserve since it is only available for about 4 hours and output that diminishes with time.
Looking at day-to-day operations, solar and wind are unpredictable, and CAISO operators must use all their smart grid data to predict changes that occur throughout the day, such as cloud cover, wind changes in direction and duration, and temperature. When clouds cover a solar farm, its output dramatically decreases, and fast-acting gas turbines or hydro units must operate in spinning reserve to make up the difference. If the wind speeds up, CAISO operators may have to decrease their wind farm supply to prevent overloading the grid. Shutting down units is an added expense that the consumer will pay. During mid-day operations, solar output is at its greatest, which may require CAISO operators to decrease their solar farm supply to prevent overloading the grid…again at the expense of the consumer. So as we build more solar and wind generation, we will need more natural gas generation or battery energy storage to back up this free energy, adding more expense. A viable option is to build more nuclear generation to increase our baseload capacity, but this takes years and until then expect electric rates to continue to increase.
