To some extent, your suspicions are correct (notice some of the nuance you could add to your four main concluding points):
Renewable adoption trends are slow.
Not just slow, but there is a wide dispersion of adoption based on point of energy consumption. (e.g., Think how many gasoline vehicles there are in the world and how long it will take to replace or ...
I believe "Auctions of Homogeneous Goods: A Case for Pay-as-Bid" by Pycia and Woodward answers your questions theoretically. This is quite recent and their results are striking. They also briefly discuss some empirical insights.
The pay-as-bid (or discriminatory) auction is a prominent
format for selling homogenous goods such as treasury ...
TMo's answer already covers a lot of very good points, but the single word 'new' in your quote already explains a large part of the problem.
If you want to create a new power source, renewables are often the cheapest option. However, if you already have an existing power plant it is a lot cheaper to just continue running it than to tear it down and replace ...
I guess the main reason why you could not find an answer is that economists do not know, see, for instance this chapter of "Electricity Markets."
The auction theorist Peter Cramton has a few papers on this.