High river flows generating a temporary oversupply of hydroelectricity caused the Bonneville Power Administration last night to partially and temporarily limit the output of non-hydroelectric energy, including fossil-fuel and other thermal generation and wind energy.
The action was required to protect salmon and steelhead, maintain the reliability of the power grid and avoid shifting costs to BPA's customers. It came as the U.S. Army Corps of Engineers increased river flows to maintain space in upstream reservoirs for further runoff from the largest Northwest snowpack since 1997.
High water and hydroelectric output combined with low nighttime energy demand led BPA to temporarily limit other types of generation beginning at 12 a.m. Wednesday. BPA first limited all coal, natural gas and other thermal generation to minimum levels required for grid stability and safety. As a last resort, BPA then limited approximately 200 to 350 megawatts of wind power generation until 5 a.m. Wednesday totaling approximately 1,400 megawatt hours. There are currently more than 3,500 megawatts of wind energy connected to the BPA system.
For comparison, 200 to 350 megawatts is about one-third of the generating capacity of Bonneville Dam. The limits have now been lifted and other generation is again operating normally. However, further limits may be needed in coming days.
Rising runoff has pushed dissolved gas levels at most of the eight federal dams on the Lower Snake and Columbia Rivers above 120 percent, exceeding Washington and Oregon water quality standards and threatening protected salmon and steelhead. Reducing hydroelectric generation in such circumstances would send more water through spillways and could push gas levels higher for longer periods, further endangering fish.
Dissolved gas levels are available in real time at the U.S. Army Corps of Engineers Water Management Division website.
The Corps of Engineers, Bureau of Reclamation and BPA are required under a court order to manage spill levels to protect fish.
BPA has taken aggressive steps in recent weeks to avoid limiting other forms of energy generation. For example, the agency has provided free or low-cost hydroelectric power to encourage other power producers to substitute it for their own power. Almost all coal, natural gas and other thermal generation in BPA's system is now off-line. Real-time generation levels are displayed on BPA's website.
BPA will provide updates on further generation limits, if any, at 9 a.m. and 3 p.m. each business day at www.bpa.gov/go/afterhours