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On May 3rd 2017 the California grid experienced its first Stage 1 grid emergency in nearly a decade.
The reasons for this emergency notice were:
– a 330 MW gas-fired plant outage
– 800 MW of imports that were unavailable
– a demand forecasting error of 2 GW
A Stage 1 grid emergency doesn’t mean a blackout – it forces the ISO to dip into reserves and slip below required reserve margins. It allows CAISO to access interruptible demand side managment programs.
I wanted to highlight two features of this event I found interesting.
1 – The demand forecasting error of 2 GW
This is a massive error in absolute terms – equivalent to a large power station!
To put this error in perspective demand on the 11th of May for the same time period was around 28 GW – giving a relative error of around 7%.
It’s important to note that this error isn’t actually an error in forecasting the actual demand – it’s distributed & small scale solar that is appearing to the ISO as reduced demand.
2 – Lack of flexibility
It was unusual that the issues began developing around the peak, and demand wasn’t ramping down much, but solar was ramping off faster than what the thermal units online at the time could keep up with in serving loadCAISO spokesperson Steven Greenlee
In a previous post I highlighted the concept of flexibility. This event demonstrates why flexibility is so important for managing a modern electric grid.
Even if you have the capacity (MW) you might not have the flexibility (MW/min) to cope with the intermittent nature of renewables.
It’s also made clear in the RTO article that interruptible demand side management programs are only called upon in a Stage 1 emergency. Prior to this thermal units are used to balance the system.
Using flexible demand side assets as a first step to balance the grid could be a more optimal way to deal with this problem.
Thanks for reading!