Oh no!
If power becomes too cheap, what then? Won't someone think of the fossil fuel companies and nuclear power plants?
I'm sorry, but cheaper power could have a large number of positive effects we can't predict yet. Yes, we have to figure out a better way to deal with excess power, but this could have the power to change the cost of a large number of things in our economies. Having more power available for less money could transform the economy in ways we can't get predict.
This isn't about cheap power. Cheap power is a good thing.
This is about power that is worth less than nothing. The only reason power can have a negative price is because it's harming the grid, and the grid operator demands that producers pay to add their damaging excess power to his oversaturated grid, in the hope that this will get some production taken offline.