Case Studies

Capturing ERCOT’s first post-RTC+B price spike

On December 14th, a late evening price spike across most of ERCOT – the first widespread spike post-RTC+B implementation – offered a sharp reminder of how unpredictable the ERCOT market can be, and how execution decisions earlier in the day can determine whether storage assets are able to capture unexpected volatility.

What happened?

Between 8:00–10:00pm real-time energy prices spiked across most of ERCOT, peaking ~$400/MWh around 9pm. The exception was the Houston Load Zone, where congestion ultimately muted the price response. Elsewhere, conditions aligned to produce a meaningful pricing event.

Several system dynamics converged in the evening hours:

Much of the storage fleet had discharged around 6pm, so fleet state of charge was depleted and, by the time prices began to rise, only ~1GW of the storage fleet was discharging.
This tightening was also visible in Physical Response Capability (PRC), which continued to decline as the evening progressed and SCED had fewer flexible resources to lean on.
Thermal outages remained elevated, hovering around ~19 GW, limiting available supply.

Capturing the peak

For storage operators, the evening highlighted an important challenge – being available when the market actually peaks, not just when it usually does.

Capturing the late price spike required a few key steps:

Preserving state of charge
Many assets had already emptied – or begun depleting capacity – earlier in the evening, when RT energy prices tend to be highest and were clearing ~$100/MWh. This left most assets with little energy to deploy when prices climbed.
Using structured PQ bid legs
Price-Quantity (PQ) bidding allowed discharge to scale with price — so we discharged modestly at lower clears and more aggressively as prices rose. This ensured that more energy was used when prices were highest between 8-10pm.
Avoiding conflicting AS positions
Having Ancillary Service offers in place during the interval could result in clearing into AS instead of RT energy because, as we know, in this post-RTC+B world, when you have multiple offers into SCED that are clearable, ERCOT gets to choose which to clear you into. Mitigating this risk with strategic bid plans is critical.

Morning rebound

The price formation anomaly continued overnight, where RT energy prices rarely dropped below $100/MWh, and into the next morning. Around 7:25am we saw another energy peak (~$250/MWh) and elevated RT AS prices, with Reg Up, ECRS and Non-Spin all clearing between $40-45 – well above their DA clearing levels of $9-16.

Since no one has a crystal ball, this dynamic makes the optimization problem a challenge.

In order to catch the RT spike and/or not run into imbalance with any DA AS obligations you may have had, operators would have needed to charge overnight. To do so at these high prices would necessitate a belief:

RT prices would be even higher in the morning
You will capture a positive spread between the $100+ cost to charge and what you are able to discharge at

Tyba’s optimizer did exactly this. Forecasting the high prices we ensured our DA AS offers were high enough that they did not clear (the flipside of which is, had they cleared, it would have been lucrative), charged up overnight, then discharged at full blast into the morning RT energy peak.