Expending energy does not give bitcoin value.
Any currency is only a share in something of value.
A physical coin can either be exchanged for its value in metal (by melting it down) - a practice that is illegal in many countries, or it is a symbol for a share in an economy. Thus, the value of USA goods and assets is $x and $1 is 1/x of the value of that.
That is inherently why printing more money causes inflation. If the money is printed faster than the value of the economy increases, then inflation occurs.
Many have said that Bitcoin gets its scarcity value because it takes a lot of energy to mine one. Yes, it is true that making a new bitcoin takes increasing amounts of energy. But that is not enough. The resulting product still needs to have value.
If I drive 300 miles to get a pebble from the beach, I cannot say that pebble is worth 300 miles of fuel, wear and tear and driver time. It is just a pebble, no more valuable than the thousands of pebbles in my driveway. It is only worth what I can con someone to believe a pebble is worth.
That's the same with bitcoins. They are just a sequence of bits. Your CD collection has billions of sequences of bits. What makes these bits special?
There is no legal framework (like there is with national currencies) that gives bitcoin value. Basically people have picked up pebbles and started trading with them. That's all fine until either:
A) People get bored with the game.
- or -
B) Someone tries to change the game. We're now trading with acorns and not pebbles.
History is littered with alternative currencies that have failed and bitcoin is just going to end up being one of those.