Alberta had free power for more than a day in August, and seven hours last weekend – how does that happen?

A weird thing happened the weekend of Aug. 23-25: For 30 hours, most of that in a block on Aug. 24, the price of electrical power in Alberta was zero dollars per megawatt. Essentially, power on the Alberta grid was free for more than a day. A similar thing happened this last weekend.
Which brings about a fundamental issue – the problem with no one getting paid is no one is getting paid.