docs(renewables): compare renewable proportion with aemo and explain the records

guides/renewables.mdx

@@ -46,7 +46,7 @@ $$
 \text{renewable\_proportion} = \frac{\text{generation\_renewable}}{\text{demand\_gross}} \times 100
 $$
 
-Where `demand_gross` = operational demand + rooftop solar generation.
+Where `demand_gross` is [gross demand](/guides/demand#gross-demand): operational demand plus rooftop solar generation.
 
 ## Renewable with Storage Proportion
 
@@ -73,6 +73,24 @@ AEMO publishes two renewable share figures in their Quarterly Energy Dynamics re
 
 Our `renewable_proportion` differs from AEMO's storage-adjusted metric in that we include battery discharge and non-hybrid pumped hydro in the renewable numerator, while AEMO excludes all storage from their adjusted figure. Our approach counts battery and pumped hydro discharge as renewable since the stored energy originated from the grid's renewable mix.
 
+### Instantaneous renewable share
+
+AEMO's instantaneous renewable penetration, the figure behind headlines such as renewables supplying 80% of the NEM for the first time on 19 September 2026, is renewable generation as a share of **total generation** (NEM generation plus estimated rooftop solar), calculated for each half hour. Our `renewable_proportion` is renewable generation as a share of [**gross demand**](/guides/demand#gross-demand), calculated for each 5-minute interval. Both count wind, utility and rooftop solar, hydro, bioenergy and battery discharge as renewable, and neither counts battery charging or hydro pumping. They differ in two ways:
+
+- **Denominator.** Total generation measures what is produced; gross demand measures what is consumed. Within a region the difference is mostly imports and exports, so a region that exports can supply more than its own demand from renewables and show a proportion above 100%, as South Australia and Tasmania regularly do. We show this deliberately. Across the whole NEM, interconnector flows between regions cancel out and the two denominators are close.
+- **Granularity.** AEMO's figure is a half-hourly value, the granularity of its rooftop solar estimates. Our interval records use 5-minute intervals, with rooftop solar interpolated to 5 minutes. Demand moves more within a half hour than generation does, so the highest 5-minute interval in an event sits above that half hour's average, typically by 1 to 2 percentage points.
+
+## Renewable Proportion Records
+
+The [records](https://openelectricity.org.au/records) feed tracks the highest and lowest `renewable_proportion` for the NEM, each NEM region and the WEM, over 5-minute intervals, days, months, quarters and years.
+
+- **Interval records** use a single 5-minute interval. The NEM figure is total renewable generation across all five regions divided by their total gross demand, not an average of the regional percentages.
+- **Day, month, quarter and year records** divide total renewable generation by total gross demand across every interval in the period. This is an energy-weighted share, not an average of interval percentages.
+- **Confirmed data.** Every record is calculated from confirmed data for every region and every interval in the period: operational demand, generation and, in the NEM since October 2015, rooftop solar.
+- **Timing.** Records are published once rooftop solar estimates for the interval are in, usually 30 minutes to 2 hours after it.
+- **History.** Records start in June 2007. NEM records include rooftop solar from October 2015. WEM records before October 2023 are calculated from 30-minute data.
+- **Precision.** Values are shown to two decimal places.
+
 ## Available API Metrics
 
 | Metric | Unit | Description |