The piece that most people miss from this analysis is that the value of mining is imputed from the value of the product of mining, not the other way around. To those unfamiliar with the terminology, this means that the value of bitcoins is what sets the equilibrium for the rate of mining according to energy costs.
Brenzi explained this in the following quote:
Energy consumption for mining has a high correlation with bitcoin exchange rate to fiat currency. Because variable costs of mining are dominated by electricity price, the economic equilibrium for the mining rate is reached when global electricity costs for mining approximate the value of mining reward plus transaction fees.
This fundamental rule is unfortunately not yet widely understood.
And there's more conclusions directly following:
more efficient mining gear does not reduce energy use of the bitcoin network. It will only raise the network difficulty
cheaper energy linearly increases mining energy use of the bitcoin network
the same conclusions apply to all proof-of-work based currencies (i.e. Litecoin).
Essentially, the way the market equilibrium will work for mining is that the rate of mining will trend towards the cost of electricity, network bandwidth, and hardware investments (both in new hardware and repair of broken hardware,) such that the amount mined (Created BTC plus Transaction Fees) equals this cost.
What must be added is that this market is actually much more complex than just the relationship between electricity costs and the value of Bitcoins. There are several other markets at play that work on a higher level of this structure of production.
One such market is that of transaction fees. If transactions aren't going through the network very quickly, this will tend to increase the market rate of transaction fees, thus increasing the return on mining investments. Such a case might come about by a shortage of network bandwidth, a factor in the cost of mining. With a higher network bandwidth, the miner will be able to handle more transactions, thus increasing the supply of available transaction processing, thus lowering the market rate of transaction fees.
Other markets include the cost of upgrades to hardware which will consistently lead to a moving target for the rate of mining = amount mined equilibrium.