Is wireless charging more or less efficient than wired?

15 November 2016

Question

Is wireless energy transfer also more energy efficient due to less power lost in cables, or is it actually less efficient as extra energy is needed to "beam" out electricity? In other words, would my electricity bill go up or down if I were to change all my outlets to wireless?  
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Answer

Chris Smith put this question to tech investor Peter Cowley...

Peter - Very, very much the latter as I'll explain in a minute. First of all, wireless charging, we already starting to use. Many of us have toothbrushes that are wireless charged. I think all smart watches are wireless charging in order to keep them waterproof. Some phones are wireless charging at the moment. So we are moving that way.

The power comes into domestic property through a consumer unit. We can't all end up bunched round the consumer unit collecting power from that, so the power has to get out in wires around the house. So, presumably, we're taking it from the point when it comes to the wall and from there, instead of plugging something into it using effectively copper and copper connection, you have wireless.

The wireless part of it means converting the AC signal, the AC power, through to a radio frequency and then back again. I'm sure it's getting better but, at the moment, you're losing about 5 percent converting it to radio frequency and back again, so that's 10 percent. You're losing about 11 percent actually through the air. So you're losing in the order of 20 percent. So if you take 20 percent as the amount you lose, how does that compare with the amount of cable that you were going to plug into it?

And you get some crazy, crazy numbers here. If you were running a full 13 amps out of that, you would need a cable that was 140 meters long to be equivalent to the loss you've got through the air, and it gets massively worse. If you actually put a phone charger, and instead of the phone charger you put RF, you'd need a cable from that point there, 100 kilometers long would lose the same amount of energy. So no is the answer in a very quick way.

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