I see this posted a lot as if this is an issue with capitalism. No, this is what happens when you have to deal with maintaining the power grid using capitalism as a tool.
The framing of it as the problem being that the price is going down rather than that excess power is feeding into the grid is what makes it an issue with capitalism. The thing you should be questioning is why MIT Technology Review is talking about some consequence of the problem that only exists because of capitalism instead of talking about the problem itself.
And before you downvote/object with some knee-jerk reaction that I'm being pedantic, consider this alternative way of framing it:
The opportunity is that solar panels create lots of electricity in the middle of sunny days, frequently more than what's currently required, so it is necessary to develop new flexible sources of demand so that the excess energy doesn't damage the power grid.
That's pretty vastly different, isn't it?