well it's at those moments, when you cannot get the megawatts down the wire as fast as they are being generated, that electrolysing water to make H2 and O2 looks sensible - you could store it locally and take it off by tanker.
Sounds pretty usual for a 'market economy' - the generators will be 'customers' of the grid - if technical problems mean that the grid can't provide the transmission service they've contracted to supply, and as a result their customers are unable to sell their produce on the open market, then any sensible contract would have a 'penalty clause' that provides for compensation to be paid. A decent lawyer would argue that the losses would be more than just the financial cost of lost sales - a loss of goodwill from the generator's customers, or extra work for the generator's employees etc. etc. would also add to the bill.
as burn notes, this is all about what it makes sense to ask customers to pay for. it's cheaper to pay generators to turn off for a few hours each year than to spend billions on infrastructure that will hardly ever be used. it also means fewer pylons.
this is the "smart grid": you can't get much more out of the assets, unless somebody repeals the laws of physics, so we end up selling non-firm capacity that occasionally has to be taken away