Bitcoin is the least efficient technology ever created. There is no limit to how much electricity it can consume just to handle 7 transactions per second. No matter HOW much electricity it uses this value will never increase.
This solution to this issue is extremely simple, but I bet it will never be implemented in Bitcoin BTC. That's one of the reasons why it forked in 1 August 2017.
There is a limit. The cost of electricity required is bounded by the value of the reward (block reward plus transaction fees). The value of the reward is bounded too, since the "import" of electricity into the Bitcoin economy is inflationary.