The kWh to maintain a BTC would mean its value would be next to zero. Considering that a select few machines could maintain all the BTC on Earth (hypothetically, if one person owned all of them). A 120W machine consumes 1.1MW in a year, that means that the entire GDP of BTC could be summed up as a very small portion of the running cost of a very small coal power plant.
For BTC to get anywhere you need people earning BTC, spending it on goods (to the degree where you can spend it at a supermarket), etc. In addition you need a flow of new BTC into the market as value is added into the market (a farmer grows a crop and by doing so introduce more currency into the market, AKA Gross Domestic Product).
The 21 million BTC limit is also extremely naive. Inflation is not caused by more money being minted, it's caused by too much money being minted (when compared to the amounts of goods produced within the producing country). Money needs to flow into the market otherwise you wind up with hyper-deflation: humans, being humans, would hoard the currency and the currency would lose its liquidity. Unfortunately someone needs to valuate the value of the goods flowing into the market and decide how much money to mint based on that - a decision needs to be made which unfortunately means a controlling authority is required.
If you could remove the 21 million BTC limit and get a couple of million people to abandon their current currency (dollars, pounds, whatnot) and adopt BTC exclusively, maybe it would work - but valuating physical goods would be tricky, as right now it's valuates on the electricity-producing capacity of a country (which is definitely not its gross value).
BTC has very good motives, unfortunately the way we have set up things (and the way that humans behave) means that it's nothing more than a blue sky dream.
