Being a data analysis geek, I've been playing with the data logs on the operation of the Hornsdale Power Reserve. You can see the live data here:
Load (charging)
nemlog-api: Unit: HPRL1 [at HORNSDAL] Output and Regional Price (SA1)
Generation (discharging)
nemlog-api: Unit: HPRG1 [at HORNSDAL] Output and Regional Price (SA1)
These links have charts the show the power price and the load taken or generation delivered by the HPR. There are also links the csv files containing the underlying data.
So this evening I was shocked to see these charts.
View attachment 277010 View attachment 277011
What is shocking here is the frequency of negative prices. Many of these prices are -$999.999 and -$1000. These are suspicious as they signal missing values. However, negative prices are all over the place and they often last for just a few 5-minute intervals. So these very well could be legitimate negative prices.
So on assumption that the data are correct I calculated how much power the Tesla battery bought and sold over this 36-hour period.
Load, -173MWh @ -$132.85/MWh = $23,045
Gen, +89MWh @ -$154.07/MWh = $13,756
Net, -84MWh @ -$110.34/MWh = $9,289
So in 36 hour the battery made $9289 while gaining a charge of 84MWh. The battery was doing rate arbitrage while the price was rapidly alternating between positive and negative prices. While the battery is quite nimble, it did seem to have difficulty following price signals in real time. If the negative prices are in fact erroneous, this would explain the difficulty. Also if the price signals are not communicated quickly enough, this would cause problems. But assuming all this is working properly, it looks like there may be opportunity to fine tune the trading algorithms for this kind of bizarre price action.
Nevertheless, if the power market is starting to experience this degree of exposure to negative prices, batteries like HRP are uniquely position to soak up these spiky negative prices.
I do hope that reneweconomy.com.au can get to the bottom of this bizarre episode. What the heck is going on?