In the EU there is actually already a market of different contingents of electrical energy with different availability guarantees. Sources with high availability are more expensive and this helps to finance the required technology. And all this works rather in an evolutionary way. For example, we can, today, predict how much wind power will roughly be generated within the next days, and we can adjust reserve capacities with different costs to even that out. It is not only feasibly but also the economical thing to do.

Yes, we do have that system and people do bid to deliver energy. We do however allow fossil fuels to be used when wind power is not producing, and such, the carbon-free reserve capacities are competing against fossil fuels on production cost without the external cost of climate change being added. The economical outcome of that is an constant increase in fossil fueled capacity in practically every country in EU, with new fossil fueled power plant being built today even when we know that the climate can't take it.

The costs and risks involved in large scale power generation facilities isn't really fit for private companies and market competition. And when you add a market element to it, companies might cut corners to increase profits ( or minimise losses), and you certainly don't want that.