By exergy I take it you mean the thermodynamic definition, yes? Excellent remark and ultimately that is the theoretical limit one would strive for, but from a practical standpoint I really don't think you need to get nearly so complicated.

Equivalent renewable-source BTU or KWh will do just fine for a long time. Just the transition alone from a purely fiat currency to one backed by "green" BTU will take decades.

I call it the "Greenback"... But if we used your exergy suggestion we should call it the "Carnot(e)".

(smile)

Regards

That is hilarious! Thanks... gave me the best laugh of the morning.

:-)