The Event
You cannot design against an event until you have defined it. This page fixes what this course means by a renewable-energy drought — the threshold, the duration and the recovery rule that every week and every assessment resolves against.
SLOP6246 · Canonical definition
A system described by its annual averages can look comfortable. The average hides the week the weather stops, and the system still has to operate through it. The first question here is therefore not how much wind and solar a system has, but what happens across the worst stretch it will actually meet — and that stays unanswerable until the stretch itself has a definition.
Dunkelflaute names a period of simultaneously low wind and solar availability. The word is enough to recognise the problem and not enough to design against it: on its own it supplies no threshold, no minimum duration, and no rule for what counts as the weather recovering. What follows supplies all three, as an operative definition — a small set of explicit choices that can be applied to a trace, argued with, and moved.
Every week and every assessment in this course resolves against this page. When a brief says the event, it means the definition below, not a new one introduced quietly in passing. Two kinds of number appear, and the specification and reference-data rows identify which kind each value is: a Course-defined value is a boundary this course chose, and a Synthetic trace value is something the course material records about the teaching trace that was generated for this course. Later sections refer back to those established values without repeating the tag. Nothing on this page is drawn from measured data, and no real electricity system is being described.
The operative definition
Six modelling choices form the test below. The final row records the version of that shared course definition. A candidate period is evaluated under all six choices.
- Region
- One synchronous area, modelled as a single nodeCourse-defined
- Sources counted
- Wind and solar, summedCourse-defined
- Threshold
- Combined wind and solar output below 12% of their combined installed capacityCourse-defined
- Minimum duration
- An event span of at least 48 hours, measured under the recovery rule belowCourse-defined
- Recovery rule
- A recovery above the threshold ends the event only if it lasts more than 3 hours; shorter recoveries fall inside the eventCourse-defined
- Season
- Winter half-yearCourse-defined
- Status
- Course definition · version 1.2 · operative from Week 1
Writing the rows down is the whole point. An undocumented threshold cannot be disagreed with, and so cannot be defended either — a definition nobody is able to attack is not a strong one, merely an unexamined one.
The line changes the answer
None of those numbers is a natural constant. 12% and 48 hours are lines drawn by this course, and moving either one changes which periods qualify.
| Move the boundary | What happens to the qualifying set |
|---|---|
| Threshold lower (stricter) | Fewer periods qualify; each must reach a lower combined-output level |
| Threshold higher (looser) | More periods qualify; shallower periods also qualify |
| Duration longer | Short lows are excluded, however far output falls |
| Duration shorter | Near-misses become events, and the count can rise |
The two interact, and both directions fail in their own way. A boundary can be tightened until this teaching trace contains no qualifying event. That does not prove the system safe; it may simply make the definition uninformative for this exercise. It can equally be loosened until so many periods qualify that the event no longer distinguishes a manageable lull from an emergency. A defensible boundary is one that still selects the periods you would have to survive.
Later in the course this page gains a control for moving the threshold and the duration and watching the qualifying set change. The relationship above is the thing to hold onto until then: the definition is an instrument setting, and the answer you get out depends on where you set it.
The reference event
The course uses one period from the shared teaching trace as its reference event, so that worked examples across the weeks are discussing the same stretch of weather rather than each inventing their own.
- Position in trace
- Hours 187–248, which is day 8 into day 11Synthetic trace
- Hours below threshold
- 61 hoursSynthetic trace
- Minimum combined output
- 0.9% of combined installed wind and solar capacitySynthetic trace
- Status in this course
- Designated reference event in the synthetic teaching traceSynthetic trace
Under the operative definition, a qualifying event must span at least 48 hours, and a recovery above the threshold longer than 3 hours breaks the event. Course-defined
The trace is generated by a seeded function published with this course, so these values can be checked rather than taken on trust. The generator writes the event as one contiguous block, so for this reference event the span and the count of hours below the threshold are the same 61 hours.
What the definition excludes
A definition earns its keep by what it refuses. This one refuses three things.
- Anything shorter than the minimum duration
- A period can fall much further below the threshold and still fail to qualify if its span does not reach 48 hours. The definition is about endurance rather than depth: riding out one hard day and riding out a long week are different problems, and this definition is about the second.
- One technology failing on its own
- The threshold applies to wind and solar combined. A still, bright spell or a dark, windy one can hold the combined figure above the threshold and so fall outside the definition, however alarming either series looks alone.
- A low that recovers for long enough
- A recovery above the threshold lasting more than 3 hours ends the event. That single rule decides whether a long spell of bad weather is read as one event or as two shorter ones.
Course-defined rule
Short recovery — the event continues
- Recovery
- 3 hours or less
- Read as
- One event, measured end to end
Long recovery — the event is split
- Recovery
- More than 3 hours
- Read as
- Two separate lows, each measured on its own
below the 12% threshold above the 12% threshold
Why this definition exists
The boundary is contestable on purpose. This course does not treat 12% and 48 hours as a universally correct definition of a renewable-energy drought. The useful boundary depends on the system being studied and on the purpose of the analysis.
What a course needs is not the true definition but a shared one. Fixing 12% and 48 hours here means that when two students disagree about whether a portfolio survives, they are disagreeing about the portfolio and not about the vocabulary.
So the sequence is deliberate. The course fixes a baseline first, then asks you to attack it. In the first assessment the boundary moves: you choose a threshold, a duration and a recovery rule for a system you have specified, and defend those choices against the consequences they produce. Reaching a different definition from the one on this page is not a failure. Reaching an undefended one is.
Where this goes in the course
Each piece of assessed work takes the definition one step further out, from naming the event to surviving it to admitting what would still break it.
- A1Define the DroughtMoves the boundary and defends the move.
- A2Site Against FailureUses the chosen event to judge how far output at different sites falls together.
- A3The 72-Hour DispatchTests whether a system survives the event hour by hour, not on average.
- A4Design for the Worst WeekStates both the event the system survives and the event that defeats it.
The last of those is the course's real test. A design that names only what it survives has answered half the question.