It's a known phenomenon in countries with high penetration of renewable energy that at periods of peak output the price of electricity can be driven through the floor.
This is an intereting analysis from west Texas where a lot of wind coming onto the system has produced negative pricing. I don't share the author's conclusions - but rather those of his colleague, the esteemed Dr Lynne Kiesling (at #11) who correctly identifies that one way to smooth out the negative prices is to build better interconnection so you can ship all that clean electricity to neighbouring markets where they have higher prices due to a lack of renewables.
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