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Q & A: Wireless electricity?

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Most recent answer: 03/30/2009
Q:
Why are we not able to produce wireless electricity? Canít we convert electrical energy in to some other form of energy and tranmit it and then reconvert back to electrcity?
- Ajish.M.Varghese
Electrical Engineer, India
A:
Yup, transmitting energy without wires is possible, but it has its problems. There are several ways of doing it. One is just to shine light from one place to another, and then use photovoltaic cells ("solar cells") to convert the light into electricity, or to use a steam generator that gets hot when the light shines on it. It turns out that if we start with electricity in one place, convert it to light, transmit the light, and reconvert it back to electricity, quite a lot of energy is lost in the process. The very best photovoltaic cells can only convert 20% of light energy to electricity (so we lose at least 80% of our energy right there). And light production usually involves heat losses.

One variation on this theme is to put mirrors in orbit and to shine sunlight from space onto a solar collector array which otherwise would be shrouded in the darkness of night, to improve its operating time. This is a better idea, but is expensive and may be unpleasant for people who live nearby, where it is daytime a little too much. And think of what would happen if the mirrors accidentally got pointed in wrong direction!

Another variation on the theme of transmitting power electromagnetically is to send it with microwaves or radio waves (some early pioneers of electricity and magnetism suggested setting up waves between the earth and the ionosphere, and anyone who wanted power could just set up an antenna to collect it). The problem here is that power would be distributed to places that are not intended to receive it. Everyone would be bathed in microwaves or radio waves and heat up a bit, just as in a microwave oven. Not only would people complain, but much of the energy would be lost in places where it is not desired. You can confine microwaves inside of conducting waveguides, but thatís even worse than the wires weíre trying to replace.

Perhaps the most promising way to transport energy without wires is in chemical energy. You can use electrical energy to, say, separate hydrogen from water, and ship the hydrogen and oxygen in a truck to somewhere else, and burn the gases in a power plant far away, making electricity there. This process probably is more efficient than sending the energy in waves, but still isnít anywhere near as cheap as putting oil and coal we find in the ground into a truck and sending it to the power plant.

Tom

(published on 10/22/2007)

Follow-Up #1: Precautions for wireless power transmission

Q:
is there any human effect? if we transmit power without using wire.
- Dhaval (age 19)
vvnagar,gujarat,india.
A:
Wireless transmission of energy at low levels is not harmful, consider radio or TV transmission from far away broadcasting antennas.   However at very large power levels, like very close to a powerful antenna, there may be problems of excess absorption of energy in the human body.  Consider a microwave oven.  You wouldn't want to stick your hand into one.  It is a matter of  magnitude, not of principle. 

LeeH

(published on 03/30/2009)

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