I assume the reason is that these "negative prices" are just fictions, only available to a few select existing customers, ie artifacts of regulation.
But the article is actually too vague for me to understand what the actual regulatory and political constraints of the situation are.
They seem pretty press-shy about it though - possibly because this is serving as a kind of covert subsidy that wouldn't look too good under WTO rules.
Transforming renewable energy in electricity is anyway pretty ... stupid (lot of loss) and counter productive (handling surge, storing, grid complexification, poor capacity planning that requires even more fossil energy in high power mode to adapt to peak in demand)
The real solution maybe to adapt our lives to the seasonality, and maybe to use wind power ... well to make wind mill for instance. Mechanic to mechanic energy transformation is not stupid.
Right now, renewable energy is a big scam that can not sustain and that is used by thieves to still tax money in the name of good intentions.
What are you even talking about? Have you invented a new mechanic energy transmission process with no losses? If we are calling names, I'd say that mechanic energy transmission is even more "stupid". If your mechanic energy collection gizmo is not right where you want it, then you'll have tremendous losses transmitting it.
Not that it matters too much in case of renewables. You just need a bigger collecting system.
Also, electric energy is fungible. You can convert it into almost anything you need, including mechanical power. Good luck posting to hacker news with your mechanical energy.
The solution is not going back to medieval era. It is to figure out better solutions. Renewable energy is not a scam. The market may be heavily subsidized (not everywhere), but that's how you jump-start an industry. Market forces may prevent development, but that's a different problem.
Not to mention that everything is subsidized in some way. Coal power plants should be paying for the pollutants (including radiation) that they are releasing in the atmosphere. In fact, all current power plants (including hydro) are subsidized. If not by money directly, by the law.
Even MIT outlets don't bother to explain why this is a bad thing, just stating that a price is negative is enough to demonstrate there's a problem.