I think the headline is a gross misrepresentation of the study. When it comes to providing electricity, cheap is not and never has been enough. It is important, and what is cheap (or was when the plant was built) tends to make up the bulk of any regional electricity supply, but more expensive generators are also in the mix because they have desirable properties that are worth paying more for (like being able to provide megawatts of electricity on demand and at short notice).
What the study points out, in essence, is that while solar is cheap, since it is up to the sun to turn it on and off there is only so much you can install before you find yourself periodically generating more electricity than you can use. The way the vast majority of our power grids are set up today, whatever electricity you don’t use immediately is wasted. It doesn’t matter that it’s cheap and plentiful if it goes to waste, and it’s hard to make a green argument around producing emissions-free electricity that you ultimately can’t even use. If that’s the end of the story then of course that’s going to be a barrier to solar expansion. The study views this through the lens of corporate profitability, but I don’t think that’s really even necessary – it should be obvious that at a certain point, we would quit building plants that produce a product with zero value and zero positive impact on GHG emissions, even if they are cheap.
Don’t get me wrong, cheap is certainly enough to get a whole lot of solar into our power grids without having to do much else beyond build the power plants. But once you’ve built a certain number of power plants, you reach a point of diminishing returns, and that occurs well before we have a fully decarbonized power grid (though experts don’t agree on exactly where that point is). That’s where the technological, regulatory, and policy solutions the study mentions come into play. And while those tools will certainly be important to getting investors in a capitalist, profit-driven economy, you will need most of them even if you make all utilities and power plants public, taking profits – let alone price-gouging – completely out of the equation.