The Bonneville Power Administration (BPA) curtailed generation during the low-demand overnight and early morning hours of June 30 through July 3 because of too little room on the agency’s transmission system.
The curtailments, similar to actions taken during the spring seasons of 2012 and 2011, were the first curtailments during a summer season, when demand is typically higher and river runoff lower.
The agency curtailed more than 9,800 MWh of generation between 11 p.m., June 30 and 9 a.m., on July 1, according to data posted on BPA’s website. The agency also curtailed more than 4,600 MWh of generation between 10 p.m., July 1, and 6 a.m., July 2, and an additional 2,600 MWh between 11 p.m., July 2 and 6 a.m., July 3.
BPA endeavors to post details about curtailments on its website by noon Pacific time about the previous day’s curtailments. No details about activity on July 4 were posted on the website, and calls to BPA seeking additional details were not returned by press time on July 5.
BPA last curtailed generation over the four-day period of April 29 through May 2. During that period, the agency curtailed over 20,000 MWhs of generation, bringing the total curtailed so far this year to more than 37,400 MWs, affecting thermal and wind generators.
In past curtailments, BPA has supplied federal hydropower to customers who otherwise would have received power from curtailed generation, including wind.
The agency does not receive revenue when replacing renewable energy with federal hydropower, and BPA officials have estimated the agency’s financial exposure for reimbursing wind producers for the shutdowns could be as high as $50m.
Prior to ordering curtailments, BPA typically orders the area’s thermal generators to reduce their output to minimum generation levels. When a thermal generation unit is shut down completely, a specified period of time must elapse before that unit can be restarted. Depending on demand, a lack of availability of thermal generation could have an adverse effect on reliability.
During this past spring and the spring of 2011, BPA curtailed wind turbines during a period of high water flows in the Columbia River. The agency was forced to route the water through power-generating turbines because spilling the large quantity of water over spillways would have increased total dissolved gasses to a level that would endanger salmon.
The curtailment prompted wind producers to file a complaint with FERC, accusing the BPA of violating contracts for firm transmission rights and of treating them in a discriminatory manner. FERC responded with an order finding that BPA’s curtailment policy represented noncomparable transmission service and requiring BPA to file a revised tariff to provide transmission service on conditions comparable to those it gives itself.
BPA filed a protocol with FERC on March 6 that is intended to help reimburse wind generators for those lost credits, but that protocol has been widely criticized by area wind producers as not going far enough (Docket No. EL11-44-000). FERC has not yet ruled on the protocol and a FERC spokesperson previously told TransmissionHub that it was not possible to predict when the agency would issue a ruling.
This story, originally published on July 5, was updated to include new information available as of July 6.