In September 2016, a windstorm caused a power blackout across the entire state of South Australia, leaving every home, business, and factory without electricity for several hours to several days. Investigators later determined that this could have been avoided if the state didn’t have so much renewable energy.
Yes, you read that right. Renewable energy from wind and solar makes electricity grids less reliable. So why is that?
One reason is the issue of ‘intermittency’. We can control the power output of most power plants by changing the burning rate of fossil fuels, the reaction rate of nuclear reactors, or the water flow rate through hydro dams. But we can’t control the sunshine or the wind. If a cloud passes overhead, the power from a solar panel drops. If the wind speed drops, so does the power from a wind turbine. This is called intermittency.
An electricity grid is in balance when supply (electricity being generated by power plants) matches demand (electricity being consumed by users). If you tried to power an electricity grid with solar panels or wind turbines alone, intermittency would make it impossible to maintain a reliable balance between supply and demand.
However, intermittency was not the culprit on that fateful day in South Australia. The high winds at the time actually allowed wind farms to meet nearly half of the state’s total electricity demand before the blackout occurred. The case of South Australia highlights a second issue with wind and solar: they weaken an electricity grid’s ‘inertia’, reducing its ability to withstand disruptions. This concept will require a bit more explanation.
As I described in my last blog (I recommend reading it now if you haven’t already), most power plants make electricity using enormous generators spinning at a speed or ‘frequency’ of 60 rotations per second. I likened these power plants to cyclists on exercise bikes, as shown in the diagram below.
If one of these cyclists suddenly becomes disconnected, the sudden drop in electricity supply will force the remaining cyclists to work harder to meet the electricity demand of the communities. If this is too much for the remaining cyclists, their frequency (pedalling speed) will slow down until they finally quit to avoid hurting themselves. This is how a blackout occurs. But because the remaining cyclists have a lot of momentum in their spinning wheels, it will take some time (maybe a few seconds) for their frequency to drop. This is the ‘inertia’ of the electricity grid, which provides a window of opportunity to avoid a blackout. When the grid senses that the frequency is starting to drop, it can decide to temporarily cut off power to Community 1. This reduces the electricity demand, allowing the remaining cyclists to power the other communities until the lost electricity supply is restored. It’s not an ideal situation, but it’s better than a total blackout for everyone.
Unlike the power plants above, wind turbines and solar panels cannot be connected directly to the grid. Modern wind turbines rotate at different speeds depending on the wind speed, and solar panels have no rotating parts at all. Power converters must be used with wind turbines and solar panels to make the produced electricity match the frequency of the rest of the grid. This is illustrated below, where red and green lines are converted to blue by the power converters. If a coal plant is like a large cyclist with high inertia, a power converter is like a tiny exercise bike with basically no inertia at all, even if it supplies more electricity than the coal plant. This makes the frequency of the grid drop faster when there is a sudden loss of electricity supply.
The 2016 windstorm in South Australia damaged multiple power transmission lines, leading to a major loss of electricity supply. In similar past events, blackouts were successfully avoided by temporarily cutting off power to certain users. But in 2016, the frequency dropped so fast that a blackout was triggered before any steps could be taken to avoid it. Why? Because by 2016, South Australia had retired all of its coal power plants and built a vast network of wind farms, significantly reducing the inertia of the state’s electricity grid.
So how are we supposed to transition from fossil fuels to renewables if this will lead to more and more blackouts? Thankfully, there are a number of potential solutions.
One year after the 2016 blackout, Tesla built the world’s largest lithium-ion battery in South Australia. The battery stores huge amounts of electricity to make the grid more reliable. It has been hailed as a tremendous success, overcoming grid disruptions and providing many other benefits as well. In my next blog, I’ll explain how energy storage allows us to use more renewable energy without sacrificing reliability.