It's still not earning you money to spend electricity because you still have to pay the transfer fee which is around 6 cents / kWh but it's pretty damn cheap nevertheless, mostly because of the excess in wind energy.
Last winter because of a mistake it dropped down to negative 50 cents / kWh for few hours, averaging negative 20 cents for the entire day. People were literally earning money by spending electricity. Some were running electric heaters outside in the middle of the winter.
Maybe, but Spain has an huge sea shoreline. Sea breeze could be here an advantage for Spain
I would assume that most countries would have natural advantages to achieve this with renewable energy sources one way or the other.
As this has been achieved by very different countries around the world.