BPA, BC Hydro cooperating to manage oversupply

The Bonneville Power Administration (BPA) and BC Hydro have been cooperating since last fall and winter to manage water flows and curb potential oversupply situations, BPA said during its spring operations call June 15.

The two utilities released non-treaty water from Canadian reservoirs during the fall and winter, creating more storage space and allowing outflows during the spring to be lower than they otherwise would have been. As a result, BPA officials said curtailments of wind generation on April 29 and 30 and May 1 and 2 were less than they otherwise would have been.

To date, approximately 20,600 MWh of wind generation has been displaced, according to BPA documents, which noted that the agency’s oversupply management protocol has not been implemented since the curtailment May 2.

“Non-treaty” refers to the Columbia River treaty, which required Canada to build three dams that would provide water storage in Canada that could be used for power generation and flood control benefits downstream in both countries.

When Canada built its dams in the 1970s, it chose to construct more water storage than was required by the treaty, according to BPA’s web site. The additional water storage is termed non-treaty storage. Access to that storage is obtained only through negotiation of operational agreements that provide mutual benefits to BPA and BC Hydro.

In addition to managing water storage, BPA has taken steps to minimize potential oversupply, including measures to ensure that the maximum amount of available transfer capacity is available on its energy infrastructure for expected times of high run-off and low demand.

BPA moved non-essential transmission and generator maintenance outages out of May and June, which historically are months when maintenance outages are common. In addition, the Columbia nuclear generating station reduced its output to approximately 85% of its rated capacity, allowing BPA to generate more hydropower and minimize the amount of water spilled over spillways.

BPA has also been employing a process called capacity-recallable energy, which allows BPA to sell energy out of its reserve capacity. The process allows BPA to “[M]ove water through the turbines when there is demand instead of during a time period where there might be insufficient demand, and might result in excessive spill,” Kieran Connolly, manager of BPA’s generation scheduling group, said during the call.

Despite those measures, BPA reported it did have to spill some excess water during the spring months, in addition to curtailing wind generation at the end of April and beginning of May.