In the long run Bitcoin mining always moves toward zero profitability. In the state of dynamic equilibrium, the cost of mining would be more or less equal to the value of the mined coins (block reward and fees). Hence there is an upper limit to how much electricity mining will consume. As the block reward halves, the power usage also halves over the long term (assuming a steady price). As the value of BTC increases, the power usage will also increase. This upper limit is independent of the number of users or the number of transactions per second, at least while fees are a small fraction of the block reward.
Some excellent points there - thank you for your input.
This is actually very interesting, because it means you can calculate the current zero profit price of BTC, which might be a nice indicator for traders. Assuming of course, that mining cost is the only force governing the value.
