We recognise that "I decided your kilo of gold is worth $50 so here's the $50 and now the gold is mine" isn't a purchase, that's theft. I'm going to assume you don't think it's insane for us to pay what the owner asked here (If I'm wrong, do let us know).

So, OK, clearly this CCGT electricity here (made with gas) offered for £85 per MWh we're going to buy that, for £85 per MWh.

Now, we also needed all this wind power which bids £5 per MWh. Presumably you'd want to pay them less than £85 per MWh. So, too bad, they bid too low, they get punished right? But since you aren't OK with paying less than the bid price, doubtless if they had bid £84 you'd pay that right?

Notice that the incentive in your model is for everybody to guess what you'll pay and bid just barely below that, whereupon you've wasted a lot of resources, your strategy no longer has any price discovery value, and you're paying almost as much as before. A triumph of... rationality?

How much do you reckon you can save the average household if you do this? £50 per year? Twice that?