Between January 13th and 16th, Winter Storm Heather hit large parts of North America. Alongside cold temperatures, the storm brought expectations of record-setting demand and grid scarcity conditions. So, how did battery energy storage systems in ERCOT respond during Heather’s coldest periods?
ERCOT was able to weather the storm without any emergency operations, unlike during Winter Storm Uri (in February 2021). In large part, this is because Uri was much more severe - in terms of temperature, precipitation, and overall duration.
However, there are still signs of progress in ERCOT’s ability to withstand extreme weather conditions. And battery energy storage systems are key to this - they provide flexibility when conditions are rapidly changing.
Battery energy storage participation aided grid operations during scarcity conditions
During Heather’s coldest days, on January 15th and 16th, batteries provided significant response to net load peaks. These peaks occurred on both mornings, as well as on the evening of the 16th.
In particular, on January 16th, solar generation set a new record: more than 14 GW of generation. This kept prices low over the course of the operating day. However, during the evening, those 14 GW ramped offline as the sun began to set.
At the same time, demand rose as temperatures fell. This combination caused real-time prices to spike. ERCOT’s bus average hub reached $1,175/MWh during the settlement interval between 6:15 and 6:30pm.
At this time, ERCOT also deployed its Contingency Reserve Service (ECRS), to provide additional supply to the system. This came in the form of fast-responding generation (like battery energy storage systems), capable of ramping to full output in under ten minutes.
On the evening of the 16th, battery energy storage systems ramped to a maximum net output of 1,202 MW. Battery energy storage systems responded similarly to net load ramps during the other price spikes - with maximum net outputs of 1,095 MW (the morning of the 15th) and 1,234 MW (the morning of the 16th).
Batteries offer the flexibility to combat short-term scarcity issues
During significant net load ramps, ERCOT often has enough overall capacity to serve longer periods (30+ minutes) of demand. However, it needs flexible resources to respond quickly to rapid changes in demand and available supply - such as battery energy storage systems.
When the price spike occurred on the evening of January 16th, ERCOT had more than sufficient operating reserves - its minimum Physical Responsive Capacity during the period was 5,133 MW. This is nearly 2,000 MW above the first typical threshold for indicating potential emergency conditions: 3,200 MW.
In contrast, the five-minute dispatch capability of ERCOT’s generating fleet had a minimum of 1,273 MW between 6:45 and 7:00 PM on January 16th.
This shorter-term capability is expressed as the High Dispatch Limit of all online generation, minus the current total generation - or HDL-Gen.
Due to the limited amount of available generation, the economic dispatch was forced to dispatch generation with higher offer prices.
Comparing overall system reserves and five-minute reserves indicates that the system only saw scarcity issues in the short term. This meant that fast-ramping assets - such as battery energy storage systems - were able to assist in resolving these short-term scarcity issues.