I'm sorry, but the "study" you refer to is nothing more than "pie-in-the-sky" dreams dressed in technical lingo. Let's examine the three points of the thesis:

1-Significant investment or spending by the state sends an important signal to other economic actors.

Well, yes. It signals that whatever it is that the state is spending money on will go through an initial period of rapid growth, until it plateaus as the spending slows, then crashes as the state finally withdraws its support.

We have almost two centuries of states trying this. I can't think of a single success.

2-Public sector investment can have a crowding-in effect whereby an initial injection of capital by the state

encourages the private sector to follow suit.

Really? Based on what? The study, of course, doesn't refer to one single example of a time when this has occurred. What ends up happening, with such regularity that it is one of the iron laws of economics, is that public "investment" drives out private investment. During the initial phase, there might be some private investment, but only enough to get a foot in the door to be able to receive their share of the public investment. Once that dries up, the private investors fold up their tents and go looking for the next lucrative public scheme.

3-Being a major procurer of goods, government can greatly influence demand, with the long-term effect of

driving unit costs down.

Again, what economic principle leads one to believe this? What historic precedent supports this claim?

This entire "study" rests on the implicit belief that "this time will be different!"

For an example that shows the contrary, with rocket launches in the hands of the state, during its entire history, it has averaged about $25k per kilogram to put something into orbit. The very first time the private SpaceX company put something into orbit it was about half that cost: $12k. With the Falcon 9, the cost is about $3k. Estimates are that the Starship will eventually get the price down to $200!

This is not an exception--it is the rule. If you want the price of anything to be as low as possible, keep government as far away as possible.

I don't believe in magic so excuse me if I remain skeptical of your rosy scenario.

If we ever do transition to clean energy, it will only be after the public financing dries up.