Duke warns solar producers it may cut power purchases

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For roughly two hours late Friday morning, Duke Energy Progress took four solar projects, putting out 92 MW at the time, off the grid, citing exceptionally low demand and operational risk mitigation.

The four projects are all owned by Duke, have a nameplate capacity of 150 MW at peak generation and were off-line from 9:45 a.m. to 11:30 a.m.

Spring curtailments are nothing new in areas of exceptionally high renewable penetration, but this is a different scenario entirely. Earlier in the week, Duke warned solar producers and state regulators that, due to exceptionally low commercial and industrial energy consumption related to Covid-19 and mild weather, they may be further curtailments down the line, with the possibility that Duke will stop purchasing power that it’s contracted to buy under power purchase agreements (PPA) with independent producers.

A Duke representative said that the warning is especially valid for Duke Energy Progress.

pv magazine spoke with Duke Energy Communications Manager Randy Wheeless who says that the company is unsure when and if the curtailments will continue and to what degree, but that the possibility exists.

As for non-solar generational resources, Duke is required to keep on-line minimum levels of dispatchable power via traditional plants, as well as reserves to meet any demand caused by intermittent generation, like solar. For any non-solar facility to be curtailed, the situation would have to be dire.

“If it got severe enough you could get to that,” said Wheeless. “Obviously we have to keep some spinning reserves available all the time for North American Electric Reliability Corporation compliance. You could get to that point, but solar is the largest intermittent resource that we have around here, so it tends to be a solar story more than anything else… We have somewhere around 200 MW that we own and operate ourselves, so it makes sense that we’re able to affect our own operations first before we go to other operators.”

Under Duke’s curtailment process, set forth by the state regulators, in any incidence where curtailment is necessary, Duke-owned systems are the first to be put off-line, as was true last week. Following Duke facilities, the next to come down would be facilities procured under the Competitive Procurement of Renewable Energy Program and Green Source Advantage Program. If that isn’t enough, Duke moves to the 5% megawatt-hour a year “dispatch down” provision included in all PPAs under the Renewable Energy and Energy Efficiency Portfolio Standard Program. The final step, if necessary, would be to impose emergency curtailments on a rotating basis, non-discriminatory basis for all the utility’s  facilities with Public Utility Regulatory Policies Act of 1978 (PURPA) contracts.