In previous posts we've seen that with just a few basic assumptions that the current reality is that utilities can only handle somewhere between 10 to 13% of Solar Generation a day before they have to start turning whole portions ("blocks") of the power plant off and then on again. However in all my examples I have used a power mix of Nuclear 15%, Coal 50%, and Natural Gas of 25% (with the last 10% coming from Natural Gas Peaker plants). You might wonder, well what if we had 100% Natural Gas? California is the closest example as it has zero Coal and gets nearly 60% of its power from Natural Gas.
So let's see how much Solar an all Natural Gas powered grid could handle. We'll start with Winter:
Above we have an all Natural Gas powered grid in Winter. If you count up the green dots you will see there are 56 of them. Doing the math, this works out to 15% of the generation for the day. So, our all Natural Gas grid can handle 15% Solar before turning blocks off and then back on.
Now let's look at an all Natural Gas powered grid in Summer:
Above we have an all Natural Gas powered grid in Summer. If you count the green dots you will see there are 66 of them this time. As we've seen before, the summer demand curve is more compatible with solar. Doing the math, this works out to 18% of the day's generation. Anything beyond 18% and blocks would need to be turned off and back on.
Next let's head back the other direction. What if you had 100% Coal and no Natural Gas? West Virginia is a pretty close example as it has 96% Coal. So let's see that:
Above we have an all Coal grid in Winter. If you count up the green dots there are 42 of them which results in 11% Solar generation. You might be thinking -- hey that example grid from before could only handle 10% -- now you're saying an all Coal grid is better? The reason is that the all Coal grid does not have any Nuclear. Nuclear is not normally turned down because 1) once it's going the fuel is essentially free and 2) you're not going to save any carbon emissions. So this all Coal grid being "better" at accommodating solar is really a smokescreen.
Finally let's look at and all Coal grid in Summer:
Above we have an all Coal grid in Summer. There are 56 green dots which works out to a 15% Solar generation -- same as the all Natural Gas in Winter example. What struck me about making these graphs is that Natural Gas is not that much better than Coal when it comes to how much Solar it can handle before blocks have to be turned off and back on. Our all Natural Gas ranges from 15% to 18%, whereas all Coal ranges from 11% to 15%. It's not an earth shattering difference.
The next question then becomes -- how much more efficient are Natural Gas plants at turning blocks off and back on again (known as "cycling") than Coal plants. We know in both types of plants fuel has to be burned to so that the turbine doesn't cool down to rapidly, and then again fuel has to be burned to warm it back up again, and all the while this fuel being burned does not make any electricity -- it is pure waste resulting in extra carbon emissions. So how big of a carbon "penalty" does this cycling impose? And what is the difference between a Coal plant and a Natural Gas plant when it comes to cycling? This will be the subject of the next post.