I'm struggling to find a reliable source about the daily electricity consumption from bitcoin miners. Would somebody point me in the right direction ?

I'm reading quite a lot about bitcoins, and one of the main potential advantages are the low transaction fees. From what I currently understand, today's fees are indeed low, since most of the miners remuneration comes from the new bitcoins.

At some point however, the supply will stop, and the whole remuneration will come from transaction fees. I would love to see some rough estimates about how much this could be.

I've seen those two: http://www.forbes.com/sites/timworstall/2013/12/03/fascinating-number-bitcoin-mining-uses-15-millions-worth-of-electricity-every-day/

http://www.businessinsider.com/bitcoin-versus-paypal-comparison-2013-12

According to this, the daily volume is currently at 250 millions usd, while the electricity costs at 15 millions usd (which seems quite huge to me). As a (very) naive estimate, supposing that all mining costs are covered as transaction fees and no new bitcoins are mined, that would account to 6% fees. Feel free to point me in the right direction if my reasoning is flawed.