True, renewable energy will save nothing.
I write a lot that the term itself should be consigned to snake oil.
In your last para, you do acknowledge a caveat, a possibility that some limitless form of energy might exist.
To me it is obvious that source is the sun.
It created, and continues to create everything we know.
In fact that is energy, all energy.
It is incorporated in all things, a static number of Joules is represented in all things physical, and most things virtual.
From the theory of Austrian Economics, we are led to understand that the issue of money must be backed by actual product.
From the theory of MMT, we are led to understand it does not, money can be issued to control supply and demand.
One makes physical sense, a means of putting fixed numbers on everything, which might equate to the Joules that created it. The other does not. And we see people lie, when it comes to them having control of money supply.
Boy do they lie!
So it has to be Austrian Economics is correct, over MMT, to stop the lies.
Now if we cast a fair eye over the available technologies, we will actually see a clear set of technologies which are actually in use, producing both fuel and money, which if we put them together, form a structure of functionality a bit like a tree.
We wouldn’t define an individual lifetime for any part of a tree, growing as it does, each leave collects the sun, dies, and is replaced, whilst the tree continues to live, grow, and supply energy in all the forms needed for all of nature.
We wouldn’t define a lifetime of the function of trees, and plants either, they’ve supplied the energy for all life as we know it, from the sun, for all time, whilst each tree and each plant lives and dies.
The key technologies we might note are proof-of-work tokens, hydrogen fuel cells, and solar cells.
The manufacture of solar cells can be clean, we can find numerous references to actual commercially available examples requiring no rare elements for production, only energy, and some very common, easy to obtain ingredients.
The same applies to fuel cells, and to all components used in proof-of-work token production.
The reason we see damaging, rare elements in some things, is in the interests of profit, we can improve margins in all things by improving efficiencies, therefore consuming less energy, which by current economics is chargeable. In that scheme, financial rewards result from improvements in efficiency.
But the game changes when our energy source is no longer chargeable, and infinite.
Cost and efficiency no longer has meaning, and when we are creating things from that, we have changed from destroying and depleting the old capital of Earth, to adding new capital to Earth.
Capital is added to Earth via the plants and trees of nature in terms of millions of years.
That capital has been significantly negatively impacted in around 150 years of human industry.
But after the switch to solar power, we will no longer be removing capital from Earth, but adding to it.
And Austrian economy, not MMT, still applies.
Since hydrogen fuel, and money in the form of proof of work tokens is increasingly being created from solar energy, already we have been adding to the capital of Earth.
The capital of Earth is no longer a fixed base of capital, but an ever expanding base of capital.
Our money systems have yet to be adjusted for that, but they will be, money has to become aligned with the Joules of energy received from the sun, as opposed to the Joules in what was previously the fixed capital of Earth.
Also since the capital creation and generation is infinitely scaleable, we don’t need to care any longer about how efficient an energy consuming process is, the energy itself arrives freely and is infinitely scaleable, so cost is no longer an issue.
That, is the physical truth of how capitalism is ending, right now.

We are moving from valuing the Joules strored in capital (work done), to valuing the Joules arriving from the sun (work in progress).
Some folk might lament that.
Personally I think the majority will be celebrating, forever.