Summary: Due to the increased and increasing use of solar and wind power, which typically has to be consumed by the end user as soon as it is generated, California's grid already creates too much power during some times of the day. This is particularly true in the winter, spring, and fall months, when demand for power to cool homes is lower. During these times, California's solar and wind power generating resources are deliberately turned off to prevent overloading the grid. Yet inexplicably, KR3 remains online generating unnecessary and unneeded power. This post explains why KR3 should be taken offline during the hours of 10am and 5pm from February to June and September to November. During these periods of vast excess power generation from other sources, the highest and best use of the Wild and Scenic North Fork Kern is not power generation — there is too much of that already — but natural flows for recreational use and environmental protection.
The deployment of renewables in California has been incredibly successful to this point on our state’s path to a green grid. However, it has brought along an unanticipated consequence: the threat of over-generation — that is, generating more power than the grid can handle. All power must serve a load, and system operator CAISO works tirelessly to equalize supply with demand. Balance has become more difficult with the deployment of renewables like wind and solar, which increasingly threaten to swamp the grid with too much energy production during daylight hours, leaving supply well above the levels of demand. That’s the risk of over-generation.
CAISO’s main strategy to prevent over-generation and balance supply with demand is called “curtailment,” which does what it says: curtail (lessen) the amount of generation by modern solar and wind generators whenever the grid is threatened. We’ll let CAISO speak for itself on the matter:
“Curtailment is the reduction of output of a renewable resource below what it could have otherwise produced. . . . Curtailing renewables results in lost opportunities for clean resources to generate all of the carbon-free power that otherwise could be produced. . . . Curtailing renewables is counterintuitive to California’s environmental and economic goals. It reduces the output from the renewable plants in which the state has invested, and could result in overbuilding renewable plants to ensure that the state meets its 50-percent renewable mandate
So curtailment as a strategy, while effective in keeping the grid safe, is not a desirable public policy. One of CAISO’s strategies to reduce the need for curtailment is to “reduce minimum operating levels for existing generators, thus making room for more renewable production.” In other words, reduce production to make room for wind and solar, keeping those more modern and rational generators online and profitable, so more will be built. That’s where the KR3 hydroproject should come in.
KR3 is a contributing cause to curtailment. Whenever over-generation is threatened, KR3’s production of electricity only adds to that threat, and causes modern generators like wind and solar to be sidelined to ensure that supply and demand balance out. The times when over-generation are threatened are ripe for reducing the output of KR3, “thus making room for more renewable production,” in the words of CAISO.
When are these times? According to the data, significant curtailment generally prevails any time between 9am and 7pm. But it massively prevails between 10am and 5pm. This chart depicts the average daily curtailment for each hour in 2022:
Note we have included for reference the theoretical maximum rate of production at KR3: 36.8 kW. KR3 almost never achieves that rate as the availability of sufficient “fuel” — 600 cfs of diverted river water — is contingent and unpredictable. Indeed, as the following chart shows, KR3 routinely generates at a small fraction of that rate. KR3 generates at its highest rates in spring, when demand is low and curtailments are high. And in all but the wettest of years, KR3 is nowhere to be found during late summer and early fall, when demand is high and the potential for “loss of load” (blackouts) is acute:
Back to the issue of curtailment, it is important to note the phenomenon’s seasonal component in addition to its hourly nature. In winter and especially in spring, demand is relatively low, forcing widespread curtailment of wind and solar assets. The following graph depicts average daily curtailments, by hour and by quarter, for the year 2022. Note how the figures begin to dwarf the KR3 reference line. Indeed, each horizontal axis line represents a ten-fold increase above the theoretical maximum power that KR3 is capable of producing:
Combining those two aspects of curtailment — hour of the day and time of year — is revelatory. The following chart depicts CAISO curtailments in 2022 between the hours of 10am and 5pm for each month of the year:
That chart shows the energy produced by KR3 is simply not needed during the hours of 10am and 5pm in February, March, April and May. Those curtailments occur at a scales of twenty to sixty times the maximum amount of power KR3 is theoretically able to produce.
But KR3 rarely gets close to producing that maximum. The contingencies of a fluctuating annual snowpack, unpredictable weather patterns, and the need for maintenance outages all conspire to limit KR3’s production to an average rate over the last 22 years of available data of just 12.0 MW:
Let’s compare the average monthly rates of production for KR3 against the massive quantities of curtailment imposed between the hours of 10am and 5pm in 2022. We’ll start with January. You can see that curtailments between 10am and 4pm (one hour short of 5pm) are more than 20 times greater than KR3’s average (9.4 MW) for that month. Again, the horizontal scale lines represent ten-fold multiples of KR3’s monthly average rate of production:
In February, renewable curtailments skyrocket, while KR3 eeks out a little more power (12.7 MW rate). Curtailments during the relevant hours that month were more than sixty to one hundred times larger than KR3’s production:
Even as KR3 increased its rate to 15.4 MW in March, curtailments again went higher, sidelining wind and solar in amounts seventy to one hundred forty times larger than KR3’s rate of output:
We’ll play out the string from here to round out the rest of 2022:
The following chart summarizes preceding charts with both the minimum and maximum multiples of renewable curtailments between 10am and 5pm by month against the KR3 average rate:
We believe these figures show that the energy KR3 produces during the hours of 10am and 5pm is not useful to society from February to June and September to November. It makes no sense to dewater the Wild and Scenic North Fork Kern during those hours when at least 25 times (and most often much, much more) the generating power of KR3 is sitting on the sidelines. And don’t forget, according to CAISO the scale of curtailments is expected to increase over the years as more and more wind and solar come online.
