I asked Claude:
"If combined wind+solar output drops to ~10% of nameplate during one of these (a standard threshold), a ~77 GW fleet sized to meet average winter demand produces ~7.7 GW against a ~22 GW cold-snap peak — a 14 GW shortfall that storage alone has to cover. That works out to roughly 340 GWh for a 1-day lull, ~1 TWh for 3 days, ~1.7 TWh for 5 days, ~2.4 TWh for a week, and ~3.4 TWh for 10 days. Ontario's entire current and under-construction battery fleet sits in the single-digit GWh range, so even a mild 3-day lull needs ~100-200x what's actually being built, and a serious week-plus event needs 400-600x — which is why lithium-ion batteries work fine for hourly duration but make no economic sense at the multi-day scale these lulls demand."