[LorenPechtel]

What happens when they bid power and can't deliver?

[jerven]

There is a significant fine to be paid by the non delivering supplier. This still happens and that is why there is also an auction for reserve power. Oversupply is fined even higher as that is also bad for grid stability.

[LorenPechtel]

And what ensures the reserves are adequate?

[ViewTrick1002]

You generally have two options:

1. Pay someone else to deliver your electricity.

2. Pay the grid operator to deliver your electricity through their reserves. This includes a fine.