Renewable energy, - if it is to be resilient enough to manage the transition from carbon based mass consumption to a sustainable future - must be accessed through a technology based on materials in plentiful supply. There's no point basing it on kryptonite or on materials that are prohibitively costly to access or convert. There is only so much platinum (or uranium, for that matter) to go around.
The idea that we can carry on regardless and simply substitute another power source for our present ones is foolish in the extreme. Carbon was a once-only offer. The party's over.
Energy is an expression of labour and time. What human or horse muscle can achieve in an hour pales beside the work rate of carbon fuelled engines. We have created a global culture that is entirely dependent on more labour and more time than is available without burning fossil fuels. When the fossil fuels are no longer available, and the alternatives prove inadequate to the immense and wasteful scale of our chosen way of life - how will the powerful seek to satisfy their "needs" for additional labour and time? In the time honoured tradition -of enslavement and conquest? How will the powerful deal with those who compete with them for labour and time? In the time honoured tradition of enslavement and conquest.
We are a predictable species, by and large (give or take the odd black swan moment)
There is no alternative energy source that can meet our "need" to have our cake and eat it too.
Reduce. Re-use. Recycle
One might add - Re-Design