Let's actually talk about curtailment a bit because there is one important conceptual thing that people often miss, which is the relevance of timing of curtailed energy. It matters a lot whether curtailed energy is spread across the year or all at once. (short thread (I hope))
According to CaISO (link) 461 GWh of wind/solar were curtailed in 2018. Could we have done something useful with that energy? It depends on how it is spread out.
We can see that there is at least an annual cycle (most curtailment in spring/fall) caiso.com/informed/Pages…
We can see that there is at least an annual cycle (most curtailment in spring/fall) caiso.com/informed/Pages…
But let's imagine one extreme: that 461 GWh is *perfectly* spread out over time. Divided over the 8760 hr in the year, it would be a constant 53 MW of baseload power.
Could we find a good use for that? Absolutely! We'd probably just use it to replace some other generator.
Could we find a good use for that? Absolutely! We'd probably just use it to replace some other generator.
Now imagine the opposite: all 461 GWh of curtailed energy comes in one (hard-to-predict) hour of the year.
Could we find a good use for that energy? Probably not. Clearly, the current system (supply and demand) doesn't want it. What kind of user wants GWs of power for 1 hr/yr?
Could we find a good use for that energy? Probably not. Clearly, the current system (supply and demand) doesn't want it. What kind of user wants GWs of power for 1 hr/yr?
Real curtailment obviously falls between these extremes, and is a mix of both. There are opportunities for storage (or whatever) to collect the regular DC-clipped energy from PV panels, for example. But there are also seasonal patterns that dump too much power in a short time.
Even the discussion on "seasonal" storage often forgets that the curtailments aren't spread evenly in the season - they are concentrated in particular days/weeks. Check this data on Sept-Nov 2018 CA solar curtailment. How big would you size your energy-absorbing technology?
If you size it for the big curtailment periods, it will have tons of excess capacity 99% of the time and that costs money. If you size it for a lower level, you'll miss out on a lot of energy during the high-curtailment periods (and that missed energy will add up to a lot).
In the end, we will find uses for some regularly recurring curtailed energy, but continue to spill other rare and high-magnitude curtailment. Success at the former doesn't suggest that the latter is easy.
PS (on that 2nd figure): I only now noticed that the data only reports hours that had curtailment, so there is actually a lot of "zero-curtailment" hours that should be in the figure but aren't. In that 3 month period, curtailment is above 500MW only 4% of the time.
Ok, you guys got me so interested in this that I did a better analysis of that 2018 California data, looking at different amounts of "energy-absorbing capacity" in MW and calculating how frequently that amount is available and how much curtailed energy it would miss.
If you wanted to capture half of CA's curtailed energy, you'd build 200 MW of energy-absorbing capacity, but that amount of energy is only available 5% of the time. If you build for decent availability of curtailed energy (20%, let's say), you still curtail 95% of the energy.
And before you say that this will all change with more RE, let me note that more RE brings up both the low periods and the oversupply periods. Frequently-available RE isn't (and won't) actually be curtailed - curtailment is always the leftover trimmings.
Adding more RE results in both more of the useful energy and more of the hard-to-use energy, so scaling up shouldn't change this picture much. This is like how a bigger turkey gives both more meat and more junk bits.
