Theory 093/Energy & Environment /Grid planning
Storage Is Sized by Variance
Storage is sized against the peak. The requirement may be set by the spread.
The storage needed to firm a renewable supply is set by the variance of the residual load rather than by its peak, so a system with a higher peak but lower variance can need less storage.
01The evidence
Storage requirements vary widely between systems with similar peaks, and the variation tracks the variability of the residual rather than its maximum.
02The tension
Planning uses peak demand and peak shortfall, which predicts storage from the maximum and misses the duration and frequency of deficits.
03The mechanism
Storage must cover the cumulative deficit between supply and demand, which depends on how long and how often the shortfall persists, not only on how large it is at its worst.
That makes variance and duration the determinants, and predicts storage should scale with the variance of the residual rather than its peak.
04What this is not
Peak sizing covers the worst hour. This covers the distribution, which predicts more storage for volatile systems at equal peak.
05Predictions
- P1Storage should scale with residual variance.
- P2High-peak low-variance systems should need less.
- P3Duration should matter more than magnitude.
06Refutation
Storage tracking peak at controlled variance would restore peak sizing.
07What it changes
It would change grid planning methods.