The Alberta Electric System Operator on April 5 directed transmission and distribution utilities across the Canadian province to shed 250 MW of load, briefly causing "rotating outages" to ensure the reliability of the overall power system, a grid official said on a media briefing, citing multiple factors.
AESO issued a grid alert at 6:49 a.m. local time after an anticipated 800 MW "supply cushion" evaporated with lower-than-expected wind generation and the failure of idle thermal generation to quickly ramp up and fill the gap, Marie-France Samaroden, vice president of grid reliability, said on the call. Two hours later, a 400-MW natural gas plant tripped offline for unknown reasons, triggering the grid operator to issue a load shed directive.
"And so it is truly a combination of many things that occurred that got us into this rotating outage situation," Samaroden said.
Samaroden identified the plant as TransAlta Corp.'s Keephills facility near Edmonton but declined to speculate on what caused the plant to trip. The company did not immediately respond to a request for information on the incident.
AESO declined to estimate how many customers lost power.
Nearly 20,000 customers of EPCOR Utilities Inc., which serves Edmonton, lost power for about 20 to 30 minutes, a company spokesperson said in an April 5 email. Likewise, about 25,000 customers of Calgary-based Enmax Corp. also lost power, for about 14 minutes, according to a spokesperson.
The outages, which followed a grid alert just two days earlier, highlight the challenges the grid operator faces with variable renewable energy generation, Samaroden said.
"In this case this morning, we called on all generation that was available to us," Samaroden added. "With that said, we are looking to improve our forecasts as best as we can. However, the reality is that we can't control the wind and the sun. And so we do our best to forecast and have mitigation measures in place, but there are things sometimes when you get multiple things occurring, like we did this morning."
Alberta has emerged as Canada's leading renewable energy market in recent years, but the industry is concerned about future growth. The Canadian Renewable Energy Association in March voiced concerns over planned market reforms based on recommendations from AESO, and which followed a seven-month moratorium on new project approvals that ended at the end of February.
The trade group views the reforms as "another significant layer of uncertainty" for Alberta's market, making the province "less attractive to investors," Vittoria Bellissimo, the association's president and CEO, said in a March 11 statement.
The comment came after AESO President and CEO Michael Law at a conference confirmed that the grid operator would open a stakeholder process to develop a draft of a restructured market design, planned for completion in the fall of 2024. New market rules are targeted for implementation in 2027.