Wireless Power

[sdimbert]

I have heard that, at the same World's Fair that he revealed what would become the radio, Marconi demonstrated "broadcast electricity."

1 - Is this true? If so, what happened to the idea?
2 - If it isn't true, is "wireless electricity" possible? I mean, on Star Trek, they're always hooking up "Power Transwer Beams" between ships... how close are we?

[Diver]

It's quite possible, but not very efficient at this point.

Any radio broadcast station is transmitting a lot of power -as much as several thousand watts. If you get close enough to a broadcast antenna while holding a fluorescent bulb it will provide light.
The problem is that the power is not broadcast as a beam, but as a very broad pattern, although it may be somewhat directional.

[sdimbert]

The problem is that the power is not broadcast as a beam, but as a very broad pattern, although it may be somewhat directional.

So, why not broadcast it "as a beam"?

I can't be the first person to think of that.

[CurtC]

Cecil has already addressed this:

http://www.straightdope.com/classics/a3_274.html

[Diver]

"So, why not broadcast it "as a beam"? ""

I think the only way to broadcast it as a tight beam would require coherent energy which I guess could be done with a maser. I don't know what the conversion efficiency of a maser is, but if it was adequate, I suspect it would be being done, since as you say, you aren't the first person to think of this.

[Arjuna34]

Not that I can top Cecil's excellent answer (posted a few posts before this one), but in short-

if you mean broadcasting power in all directions, so everyone can tap in, it's incredibly inefficient, and dangerous. People are worried about fractions of a watt of electrical energy from cell phones- but you'd need to dump megawatts into the air to power a small town (not even taking into account the enormous inefficiencies.

If you mean in a tight beam- fine, just use a laser or some other highly focusable source. But now, just one destination can receive it- so what's the point? It'll still be much more expensive than copper wire, and much more unreliable. Of course, you could imagine a grid of receivers and transmitters, each receiver only taking the power it wanted, and re-transmitting the rest. This would let you serve more than one customer but would be even more expensive and complex.

You can't get much simpler, cheaper, and reliable than plain old wire.

Hmm, guess this wasn't so short after all

Arjuna34

[scr4]

One could also use microwaves to beam power from one place to another, as has been suggested for solar power satellites. The satellite power receiver is usually conceived as an antenna farm a few miles in diameter. At that density it's safe enough to walk through it, but not safe enough to live inside.

Crystal radio sets use "broadcast power," i.e. the power of the radio wave itself. Other than that, I can't see any practical small-scale applications for beaming power. No cordless extention cords in the works.

[justwannano]

Back in the olden days when I was servicing TVs and CB radios were popular Some nimrod transmitted a carrier all day long. The mike was keyed and no one was saying anything. Finally the head technician swore and said "allright I've had enough of this." He went to the store room and grabbed a fluorescent light tube and a mobile CB antenna.Jumped in his truck and was gone. About 1/2 hour later the carrier went quiet.10 minutes he was back at the shop grinning. "I found it" he said."A college kid dropped his mike between the seats and went to class."
He had used the antenna as a direction finder and when he found the parking lot he just walked around until the tube glowed.

[casdave]

About five years ago a fine of over £40 000 was imposed on a man who had found a way to steal power from RF transmissions of British Telecom.

He lived on a small bump in the middle of a valley and built himself a metalwork tower with his recieving equpiment on it.It was directly in the path, of a BT transmission dish which was sevaral miles away.

It took BT years to work out why the efficiency of that transmitter was low.

The guy was seen at the time as something of a Robin Hood as BT were making enormous profits at the time, upwards of £700mill.

The law did not cater well for this type of theft simply because it had never been envisaged. The beam went over this mans property and he was claiming it violated his airspace. It all got rather complicated.

So to answer the OP , yes it can be done, but it is probably not efficient or economically viable.

[CurtC]

casdave wrote:
About five years ago a fine of over £40 000 was imposed on a man who had found a way to steal power from RF transmissions of British Telecom.

If by "steal power" you meant that he was able to put this power to use, this can't be right. Maybe he just blocked some of the power by putting his tower in the way, but there's no way with a microwave link to get enough power to drive anything, especially being several miles away.

[Timothy Campbell]

We could, as somebody pointed out, move power through the air by shooting high-power laser beams. This has seriously been proposed as a means of powering space ships (in conjunction with an ion engine).

The reason we don't do it on earth, I suspect, is that if we did, the ground would be covered with bisected birds.