Again, for most of agricultural history, energy was not used to grow food. The key commodity was land. The concept of energy you're referring to didn't come along until the 1800s, a couple thousand years after people invented the coin, and didn't have any real economic meaning until the industrial revolution.

I get where you're trying to go, but I just don't think it makes sense. If you're serious in trying to find some sort of fundamental thing behind money, you might read Buchan's "Frozen Desire".