Could the NEM run without coal?
Choose a future grid: how much wind, solar and storage. Then test it against real weather from Australia's east coast grid, every half hour, and see whether the lights stay on.
The same grid is tested in every year. Only the weather changes, so you can see which years were hardest. Each year runs from August to July.
Your future grid
Other supply
Share of each year's actual coal output.
Share of each year's actual gas output.
× the 2025 to 2026 level, applied to every year.
Storage
All storage, including the batteries and pumped hydro of today.
Starting grid: 40 GW wind, 35 GW solar farms, 45 GW rooftop solar, 200 GWh of storage, no coal and 20% of gas.
Demand unmet by month (GWh)
Capacity factors: average output as a share of what was installed. These are the weather the grid is tested against. The calmest week is the lowest 7 day average for wind.
Each chart runs the selected weather many times, changing one thing while keeping your other settings. The green dashed line is the NEM reliability standard. The scale is logarithmic so small shortfalls stay visible. Long periods take a moment to calculate.
How it works
Each half hour's real wind, solar farm and rooftop solar output is divided by what was installed at the time. That gives the weather on its own, as a share of capacity. Your chosen fleet is then multiplied by that weather, so the same grid faces every year's conditions. Demand keeps each year's daily and seasonal pattern but is scaled to the 2025 to 2026 level.
If supply is higher than demand, the surplus charges the storage until it is full, and anything beyond that is curtailed. If supply is lower, the storage covers the gap until it runs empty or reaches its power limit. Whatever is still missing counts as a shortfall. The storage starts full and, in the five year run, carries over from one year to the next.
Inspired by Andrew Grogan's Open Electricity Simulation spreadsheet (2024), shared in his LinkedIn post. Data: AEMO via NEMOSIS, with rooftop solar capacity from AEMO's published figures. See Replication.
What it leaves out
- The whole grid is treated as one place, with no transmission limits between states.
- Weather is taken from actual output. In recent years some wind and solar output was curtailed when prices were negative, so the weather is slightly understated.
- New wind and solar farms are assumed to see the same weather as today's farms. In reality, spreading them across more locations smooths their output.
- No costs, ramping limits or minimum running levels for generators.
- Hydro follows each year's actual output, including the effect of rainfall.
- The real reliability standard applies to each region and to expected outcomes over many possible years. Here it is applied to the whole NEM as a rough benchmark.
- Gas and coal follow each year's actual output pattern, scaled by your settings. They are not dispatched to fill gaps.