Solar power's reliability contribution to the Electric Reliability Council of Texas may be nearly exhausted if solar capacity reaches 20 GW by 2023, a consultant told stakeholders Aug. 29, which would necessitate increased dispatchable and flexible resources to meet increasing ramping needs.
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Electrical engineers define effective load-carrying capability as the amount a system's loads can increase when a generator is added while maintaining the same reliability index, typically the loss-of-load expectation. Perfect ELCC would be 100% of a generator's nameplate capacity, but that is nearly impossible, even for conventional generation.
In a presentation to ERCOT's Supply Analysis Working Group, Astrape Consulting owner Kevin Carden said solar penetration on the ERCOT grid results in the following variations in that solar capacity's ELCC:
- 1 GW: 78%
- 10 GW: 51%
- 20 GW: 20%
- 25 GW: 5%
As of the end of July, ERCOT had a cumulative total of 8.7 GW of solar capacity installed and approved for commercial operation and another 3.7 GW that is synchronized, meaning it feeds energy into the grid but is not approved for commercial operation.
Another 2.4 GW has signed interconnection agreements and financial security posted so it could be added in 2022, and another 10.8 GW has signed IAs and financial security posted so that it could be added by the end of 2023.
Weaker forwards seen
Forward traders may foresee less risk, however, as 2023 currently has the highest average annual on-peak forward price at the ERCOT North Hub, $91.65/MWh, in the mid-term future, dropping to about $67/MWh in 2024 and about $59/MWh in 2025.
ERCOT's May Capacity, Demand and Reserves Report assumed solar capacity to have a summer ELCC of 81%, compared with ELCCs for wind ranging from 20% for turbines away from high-wind areas to 57% for coastal wind areas.
As the study indicates a "steady, persistent decline in the solar ELCC as we get to the penetration levels that we're expecting to see in the near future," Carden said, "we do think that will be a material finding."
Walter Reid, an Advanced Power Alliance technical and regulatory consultant, pointed out that the Astrape study's results look upon solar as "a silo" of one particular resource, when solar additions are increasingly being linked to battery storage or large flexible loads, which could mitigate the decrease in ELCC as solar capacity grows.
"That's certainly correct," Carden said, adding that his organization plans to complete by Sept. 9 a draft result of the ELCC study, which is also combined with a reliability study regarding the deliverability of resources to the six load zones across the ERCOT grid, with final results to be released by the end of September.
New resource adequacy measures
In a related matter, Pete Warnken, ERCOT senior manager of resource adequacy, said his organization is working to develop resource adequacy measures for the CDR that would address issues such as how much of a margin of dispatchable capacity ERCOT has in relation to "net load," which is forecast peakload minus intermittent renewable resources that may become unavailable due to nightfall or a drop in wind speed.
"They're just presented for discussion purposes only at this point," Warnken said. "The current planning reserve margin focuses on typical or normal or average conditions for the system, and of course, that falls short, when you've got ... an intermittent renewable resource fleet that's ever growing. ... So, the basic question is, is there enough to cover a worst case or something that's close to a worst case in terms of net load ... over the next five years."
The most critical periods when dispatchable generating capability would be needed is in the early afternoon, when windspeed often drops off, and early evening when solar output decreases to zero, Warnken said.
And not only must this generation be dispatchable, but it must be able to ramp up quickly enough – typically within two hours – to meet needs that may only be anticipated shortly before intermittent renewables stop generating.
Warnken said dispatchable and flexible capacity could include load-managed resources, either as an adjustment to firm net load or as resources themselves.
Economic demand response
Eric Goff, another energy market consultant, said firm net load should also account for economic demand response, which occurs when large wholesale power consumers curtail load in order to avoid excess transmission charges or scarcity power prices.
"If you don't, I think the results are meaningless," Goff said. "Because there is a demand response, and the more often that high prices happen, the more incentive there is for demand to figure out how to respond to prices. ... I know it's complicated, but I don't know how meaningful the [scenario] will be without at least attempting to do something with it."
Warnken said he agreed and while the results are "going to be pretty imprecise, but again, we do that with other inputs in the modeling."
The next CDR is expected to be released in December, Warnken said. Reports about ERCOT's dispatchable and flexible reserve margins remain under study, and are unlikely to be added to the upcoming CDR, he said.