Winter has a way of showing what engineers describe as margins for error, and contingencies or unexpected events. When the snow on the road makes your car slide before coming to a stop, you lower your driving speed and increase the distance between you and the car in front of you.
Coal vs. renewable energy is central to two current debates about energy in official arenas. These are the Environmental Protection Agency’s Clean Power Plan rule-making for reducing CO2 from power plants, and the PJM power pool’s Capacity Performance Proposal for ensuring reliability contributions from power plants. (Yes, both of these efforts chose in 2014 the initials CPP.) PJM is an organization that coordinates the movement of electricity across all or part of 13 states.
Snow can make you reconsider your planning. Credit: M. Jacobs
Much of the debate about coal vs. renewable energy has been cast in absolutes, and that really doesn’t help clarify the issue. The question is not, “Can we today use 100% renewable energy?” or “Is windpower 100% reliable?” The question is, “Does the addition of wind or solar add to the reliability of the power system?”
In both these CPP debates, the defenders of coal are ready to ignore any contribution to reliability from wind and solar power plants, regardless of size. They are saying that the fact that there are times when the wind is not blowing at a particular location (or that the sun is weak in winter, and gone at night), means that there is no contribution to meeting energy demands, none.
Calling in the heavy guns
I will get into the technical details in a moment, but let me bring in my supporter in this fight, the U.S. Army. I’d like you to picture a tough talking soldier that has seen solar panels help in some field operation. In comments objecting to the PJM changing who gets paid for reliability contributions, an Army lawyer at Fort Belvoir wrote “PJM’s proposed Capacity Performance Resource construct does not appropriately value the continuing contribution of renewable resources in meeting PJM’s capacity requirements.” (I know, not exactly the stirring words that might be written on a monument, but still helpful.) The point is, the Army believes that a contribution is a contribution, even if it is imperfect.
And that is the way all the conventional power plants get treated. There are probabilities of a forced outage with any type of power generator. Grid operators are always dealing with unexpected events, known as contingencies. The American Wind Energy Association just released a good review of this. Because there are also errors and probabilities in the forecasts of energy demand, reliability is always measured in terms of probabilities.
Assuming the worst
In the debates about reliability, the fossil fuel interests and the most conservative reliability assessments have assumed the worst. In reality, the reliability of generators, both those with fuel and those using renewable flows of wind and sunshine, are adjusted downward to reflect the probability that there will be some disruption, and times that an individual plant is not running. Rather than use the maximum capability of a plant in these calculations of reliability, the practice everywhere is to “de-rate” the generator or reduce its capability by a known fraction. This has been done for coal plants, gas plants, windfarms, and solar arrays.
On the flip side, in the worst assessments of the EPA’s CPP, the detractors have made assumptions from a table of possible plants retirements found in an EPA appendix. The assumption that all these plants will be closed—and closed on Day One of the compliance period—is just plain wrong. Clean air rules in the past have required specific plants to either close or be modernized by a date certain, but the CPP does not. Over time, some of these plants will close. In the transition, these plants could remain open and run on days of greatest need until replacement plants or wires are ready. See more reviews of the flaws in CPP critiques here and here and here.
What the debates have skipped is the description of grid reliability as a “loss-of-load expectation,” with “load” referring to the total customer demand, itself a number that varies by hour of the day and season of the year. The broadly used target for loss-of-load expectation is described as “one day in ten years.”
Planning to use what is already there
The question PJM has chosen to ignore in its rules, and that EPA detractors have ignored, is this: what contributions can renewables make? What is the contribution from a solar array which (obviously) only operates in the daylight hours? How about a windfarm that has a probability of producing under 20% of its full capability on the days of greatest demand? PJM has chosen to leave these contributions out of its loss-off-load expectation calculations completely.
PJM’s “Capacity Performance” construct requires a generator to take on a risk of paying high penalties if the plant does not perform in any hour when the power is needed. That’s not crazy, but PJM is proposing to ignore all generators that are operating but decline to take the financial risks. PJM will estimate the need for new power plants with its calculation of loss-of-load expectation using zero contribution from windfarms and solar arrays that operate for the clean energy goals and payments.
This is where the Army stepped in to disagree.
PJM has backed into this by thinking aspure economists setting “market rules.” PJM’s engineers are given these market rules, and told to use the assumptions and results that are built into this particular market construct. In the case of the preliminary reliability assessments, simplifying assumptions about power plant contributions are unhelpfully skewing the debate.
If you have followed all this, let me suggest the reliability assessments should be much more subtle, such this one from PJM and this by the North American Electric Reliability Corporation.
The crazy thing is, these better reports on reliability are from the same organizations that are now doing such a lame job on the topic. You can see, some strange alliances have to be formed before we can get out of our fossil fuel mindset.