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SACRAMENTO, Calif. (AP) — Energy regulators are blaming blackouts last summer that affected hundreds of thousands of Californians on poor planning, electrical market problems and a heat wave that blanketed the West.

Wednesday’s report covered rotating blackouts on Aug. 14 and Aug. 15 that affected 800,000 homes and businesses.

It says California was sweltering under a “historic” heatwave, and so were other Western states, making it harder to import extra electricity.

The report says California also didn’t properly plan for supplies to cover evening hours when solar power production fell.

Regulators say they’re already planning how to avoid similar blackouts this summer.