As the capacity of coal power sinks towards the level of demand
This is a short story to explain why intermittent inputs from the sun and wind can’t power a sustainable energy system.
Spoiler: Its all about the wind droughts. Especially at night.
First, three important features of the power supply and what that means.
- Input to the grid must continuously match the demand
- The continuity of RE is broken on nights with little or no wind.
- There is no large-scale storage to bridge the gaps.
Conclusion. The transition to wind and solar power can’t proceed with current storage technology.
Second, wind droughts happen.
Most people assume that the wind is always blowing somewhere not far away and we are assured of that by windpower enthusiasts. Australia is supposed to have wonderful wind resources, and wonderful solar resources as well.
We certainly have wonderful wind watchers, led by Anton Lang and Paul Miskell and his helpers. Over a decade ago they sounded the alarm on periods of very low wind across the whole of SE Australia that can last for days.
They showed the way and now anyone can monitor the wind power supply day and night, minute by minute, drawing on the cornucopia of information available from AEMO, The Australian Energy Market Operator. The suite of resources available for wind-watchers is itemised in the second part of this briefing note from The Energy Realists of Australia. All of the briefing notes are available here.
For example, look at the NemWatch widget provided by the great RE supporters at Global Roam. The two peak periods of demand for power are breakfast and dinnertime so we can look at the widget at sunrise and sunset to see how the system performs when there is little or no sun at all, and often enough very little wind.
The picture below was taken at dinnertime, just before solar power faded out for the day.
LOOK FOR THE GREEN PARTS OF THE BARS WHICH REPRESENT WIND
Sometimes there are several periods of severe wind drought in quick succession. June 2020 was the worst case in recent times, before that June 2017 had a 74-hour period of drought with several shorter episodes.
The most serious episode in very recent memory was a spell of 40 hours in August 2022.
Below is a highly simplified picture of the way we are approaching a critical tipping point in the power supply as conventional power capacity (mostly coal) has run down since the turn of the century. Up to the closure of Hazelwood in 2017 there was enough spare capacity to buffer the effect of unplanned outages and the peaks of demand at dinnertime during very hot and very cold weather.
Meanwhile the penetration of wind and solar power rose from zero to reach 36% of demand last month. The expectation is that coal will continue to exit the system and RE will continue to rise.
Demand varies in a predictable way over 24 hours, with a small peak at breakfast time and a larger peak in the evening, just as the sun is fading away. Hence the first pinchpoint in supply comes at the evening peak.
That happened during a heatwave in 2019 and there were rolling blackouts in some parts of Melbourne but otherwise a combination of mild summers and load shedding kept the grid up until the drama in June last year.
If coal continues to exit then the time will come when the supply of conventional power is short of the base load, the lowest level of power that is required day and night. Then the proverbial will hit the fan every time the wind slackens to a point where it cannot make up the difference between the downward sloping line of conventional power and the horizontal line representing demand.
The RE enthusiasts expect that increasing the capacity of wind and solar will ensure that the gap is closed but on windless nights there nothing to fill the gap. Heroic load shedding (widespread rolling blackouts) will be required to maintain the integrity of the core of the grid and avert a system black.