Can you use a optical fiber for electricity?

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Offline yor_on

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Can you use a optical fiber for electricity?
« on: 06/03/2009 13:18:53 »
Which ways can we convert coherent light to electrical power.
Would it even work?

And what would the 'energy loss' be if we did so?
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Offline Vern

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« Reply #1 on: 06/03/2009 14:57:25 »
I don't know if coherent light matters. Solar cells are still not efficient enough to get a reasonable pay back, the last time I checked. It costs about $20,000 for a roof size unit.

We have some sizeable power plants in our western deserts that use an array of mirrors to reflect sunlight onto a boiler. Each mirror has its own pointing motors and sensors. It is pretty efficient but the location is a long way from where the power needs to be used. Our government is planning to enhance the power grid to include these remote power producers.
« Last Edit: 06/03/2009 15:00:32 by Vern »

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Offline tony6789

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« Reply #2 on: 06/03/2009 17:01:15 »
yea deserts are pretty much the best way of "using whats at hand"  but as for any other ways of using ANY type of light for elctricty i dont know of any other practical things besides solar cells
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Offline yor_on

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« Reply #3 on: 06/03/2009 18:53:55 »
I meant like similar to this
http://www.freepatentsonline.com/4500803.html

We are going to have some really bad weather if 'global warming' is correct.
So we lay fiber cables at the bottom of our oceans, and dig it down.
And to transport electricity as light might mean less 'energy loss' perhaps?
also I thought we would 'standardize' it :)
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Offline Vern

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« Reply #4 on: 06/03/2009 20:25:50 »
That is an interesting invention. Magnetohydrodynamics is something I know very little about. I know it works, but I suspect a fibre optic transmission line couldn't move much power. I'm sure the present designs couldn't. The current cables require an amplifier spaced every half mile or so to keep the signal pumped to strength. 

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Offline syhprum

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« Reply #5 on: 06/03/2009 20:26:22 »
Converting electricity to light and then back to electricity is even less efficient than than using electricity to generate Hydrogen and then using the Hydrogen to generate electricity.
The best way to transmit electrical power is over regular high voltage DC cables, it might be possible to reduce the losses a little by using superconductivity but the economics are marginal.
syhprum

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Offline yor_on

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« Reply #6 on: 06/03/2009 21:13:53 »
"There have been a succession of newer transatlantic cable systems. All recent systems have used fiber optic transmission, and a self-healing ring topology. Late in the 20th century, Communications satellites lost most of their North Atlantic telephone traffic to these low cost, high capacity cables"

Does anyone know how do they solve the amplifying problem down on the bottom?
And if i remember right there are different materials inside a fiber to keep the coherent wave moving 'correctly' too?
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Offline Vern

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« Reply #7 on: 06/03/2009 21:41:49 »
The undersea cables have amplifiers spaced at regular intervals. Electrical power lines are in the cables to power the amplifiers.

The glass fibre in the cable has a glass core surrounded by a glass sheath. The sheath is fabricated to give light a slightly faster speed than the core. This keeps the pulse in the centre so that it doesn't diverge in its direction of movement.   

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Offline yor_on

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« Reply #8 on: 06/03/2009 22:22:33 »
Yep :)
So what we would need, would have to be some material that was nearly superconducting for it to work then.

Eh, you wouldn't happen to have one laying around Vern?
Just asking :)

Well, back to the drawing board, again.

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Offline Vern

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« Reply #9 on: 06/03/2009 23:13:37 »
I think syhprum had the solution. Transfer power via high voltage DC current so you eliminate the RF losses. Then we use superconducting cable and so eliminate IR losses. Quick; lets file a patent [:)]

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Offline yor_on

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« Reply #10 on: 07/03/2009 00:29:56 »
Come on, they're closing soon.
We better run.
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Offline Chemistry4me

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« Reply #11 on: 07/03/2009 00:32:47 »
But they're open 24/7.
Are we going to sleep yet? [:)]

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Offline yor_on

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« Reply #12 on: 07/03/2009 00:39:40 »
So nice of you to drop in Mr Chem.
I couldn't by any chance interest you in a new theory?
It involves waves that refuse to move,

they'll satisfy themselves by just doing 'it' instead..
The wave, I mean.

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Offline Chemistry4me

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« Reply #13 on: 07/03/2009 00:41:30 »
Go on, tell me about this theory, please.

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Offline yor_on

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« Reply #14 on: 07/03/2009 00:44:56 »
They are waves, ok.
But doing the wave.

Can you see the implications here :)
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Offline Chemistry4me

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« Reply #15 on: 07/03/2009 00:50:02 »
Nope. I am afraid that I cannot see the implications here [:(].

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Offline yor_on

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« Reply #16 on: 07/03/2009 00:51:22 »
Ok, consider a spherical cow, no, I meant stadium.
then look at the gallery, see them sit, see them stand.
And now, the wave.

As you can see it's the absolute same, but totally different, like a mirror. And as Vern pointed out to me, we can patent it too.

---

Interested?
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Offline Chemistry4me

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« Reply #17 on: 07/03/2009 00:52:37 »
You mean like a Mexican wave?

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Offline yor_on

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« Reply #18 on: 07/03/2009 01:00:07 »
Sorry, You probably got stuck on that spherical cow. that was a colleague of mine who got herself hired by the American Dairy Council to help optimize their milk production. She went around to the pastures, to the milking stations, and she looked at the scaling of the distribution networks (definitely not scale-free), etc. After a few  months, she had her presentation prepared. The auditorium was packed. She puts up her first slide and says “First, assume a spherical cow….
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« Reply #19 on: 07/03/2009 01:07:24 »
Well Mexican waves or Kiwi waves, they will work, all of them according to my new theory. But it does not, and I will repeat this, not, involve spherical cows, only innocent waves. And as I know that you are in good renown at your local ocean, you apparently don't even need to blink, no matter what waves comes your way, I just thought it might be of interest.
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Offline Chemistry4me

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« Reply #20 on: 07/03/2009 01:10:27 »
Indeed, very interested.
So what is your new theory?

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« Reply #21 on: 07/03/2009 01:14:56 »
Well as you know we are in a secured location here, but just to be totally secure I would suggest us both to lock ourself into our bathrooms and then flush down our keys. And whatever you do, unplug that computer before you lock yourself in. Internet is not a safe place to be, take my word for it. Then send me a post, I'll be waiting here.
« Last Edit: 07/03/2009 01:33:33 by yor_on »
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lyner

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« Reply #22 on: 07/03/2009 11:48:12 »
As a method for transferring power (rather than information), optical fibres are a waste of time because of the absorption in the material. DC or low frequency AC through copper cable wins in every case - except when you can't achieve actual physical contact between the source and the consumer.
Light travels without loss through space. The problem is that it spreads out (however hard you try) and the good old inverse square law comes into play eventually. Lasers simply put off the problem a bit.

Light detectors / convertors are highly inefficient interfaces with electrical energy.  A more efficient way than using light would be to use a much lower frequency of Electromagnetic Wave. Microwaves can be generated with about 30% efficiency and can be received and rectified with a similar efficiency. (Very rough figures, of course)
Unfortunately, the 'spreading loss' over a long distance is enormous unless you use really vast reflectors to beam and receive the power.

It would be interesting to see what solution 'they' would use if they needed to feed substantial power (say, a few kW) across a gap of a few hundred km  with no actual physical connection. A hideously expensive problem to solve.
Possibly a high power chemical laser could be an answer.

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Offline Vern

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« Reply #23 on: 07/03/2009 15:32:29 »

If I were to be the "they" I think I would consider Microwave Power Transmission
since we already have the technology pretty well worked out and know pretty well what the efficiency of transfer would be.

Quote from: the link
Microwave power transmission (MPT) is the use of microwaves to transmit power through outer space or the atmosphere without the need for wires. It is a sub-type of the more general wireless energy transfer methods.

Following World War II, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. In 1964, William C. Brown demonstrated a miniature helicopter equipped with a combination antenna and rectifier device called a rectenna. The rectenna converted microwave power into electricity, allowing the helicopter to fly[1]. In principle, the rectenna is capable of very high conversion efficiencies - over 90% in optimal circumstances.

Most proposed MPT systems now usually include a phased array microwave transmitter. While these have lower efficiency levels they have the advantage of being electrically steered using no moving parts, and are easier to scale to the necessary levels that a practical MPT system requires.

Using microwave power transmission to deliver electricity to communities without having to build cable-based infrastructure is being studied at Grand Bassin on Reunion Island in the Indian Ocean.

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lyner

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« Reply #24 on: 07/03/2009 21:10:04 »
yebbut is it actually done?

I should have thought that the 'green' methods of wind and wave power would be far better value for an island. Either way, you would be talking of ££ per kWh, compared with the >=10p per unit in the UK.
« Last Edit: 07/03/2009 21:13:55 by sophiecentaur »

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Offline Vern

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« Reply #25 on: 08/03/2009 00:22:35 »
From what I can glean out of the article MPT would be a trade off. It would cost much more per KWH but would not require the infrastructure connection. So you save on initial cost of the infrastructure, then pay for it forever [:)]

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Offline wolfekeeper

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« Reply #26 on: 08/03/2009 02:53:45 »
It's been proposed to use across the Straits of Gibralta for example- laying cables is very expensive. Beyond a certain point it's cheaper to just waste some of the power than try to deploy a very expensive system due to ROI issues- if it takes longer than 5 years to break even, you're usually not going to, ever, due to compound interest; and then a slightly less efficient system like MPT can win.

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Offline erickejah

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« Reply #27 on: 08/03/2009 22:01:56 »

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Offline Vern

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« Reply #28 on: 08/03/2009 22:29:55 »
Return On Investment

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Offline erickejah

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« Reply #29 on: 08/03/2009 22:41:27 »
:) tx

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lyner

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« Reply #30 on: 08/03/2009 22:43:14 »
It's been proposed to use across the Straits of Gibralta for example- laying cables is very expensive. Beyond a certain point it's cheaper to just waste some of the power than try to deploy a very expensive system due to ROI issues- if it takes longer than 5 years to break even, you're usually not going to, ever, due to compound interest; and then a slightly less efficient system like MPT can win.


How about the ships passing through the straits? Isn't there some serious hazard involved?

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Offline wolfekeeper

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« Reply #31 on: 08/03/2009 23:22:58 »
How about the ships passing through the straits? Isn't there some serious hazard involved?
No, not at all. If the beam is quite diffuse (if you have relatively big collectors at each end) it's no more dangerous than the radio waves emitted by your cell phone.

In fact, you mustn't make it too strong, otherwise you would fry all the birds that fly past- normal radio transmitters have the same problem if you think about it.

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« Reply #32 on: 09/03/2009 13:45:26 »
How big would you need these collectors (and transmitting array ) to be - bearing in mind the diffraction limit etc.? If cost is a factor then you couldn't be talking in terms of hundreds of metres of aperture. A cable would be cheaper than that!
Actually, 'normal' transmitters don't have the same problem at all. The beam from most transmitting antennae is very wide because the power budget of a comms or broadcast system doesn't require spreading losses of (as you imply) a very few dB.
Broadcast transmitters may use many kW of power but the actual power density is very low.
The only really large reflectors are used for radiotelescopes.
Basically, you would have to produce more calculated figures before you could come up with a convincing argument about possibilityof a competetive wireless sytem which provides tens of kW rather than mW of received power.
Transmitting amplifier efficiency, even, is unlikely to be much better than 60% and I have no idea what form of 'detector' circuit could produce useful output power.

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Offline wolfekeeper

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« Reply #33 on: 12/03/2009 04:02:06 »
The demonstrated power with this kind of system was a few tens of kilowatts IRC.

It's similar tech to radio telescopes except you don't even need to make it steerable. The transmitter dish can be made out of little more than chicken wire, and doesn't have to be a single dish or anything (although they need to be contiguous due to the 'thinned array curse'). It probably needs to be quite tall (30 meters ish), but otherwise there's nothing particularly notable.

The receiver can be made of something called a 'rectenna'; it's pretty much just wires strung less than 1 wavelength apart with capacitors and diodes on it that rectify it and output a DC signal when you shine microwaves on it.

It's all really simple stuff. The overall efficiency can fairly easily be over 50%, even at extreme ranges, which is low by powerline standards, but then again you don't need to worry about people cutting the cables by mistake.

The sizes as a function of distance are diffraction limited and fairly straightforward to calculate.
« Last Edit: 12/03/2009 04:04:46 by wolfekeeper »

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« Reply #34 on: 12/03/2009 11:06:17 »
I can't believe that such a system could be as good as 50% efficient (and that, I'm sure, can't include the efficiency of the transmitter).
What frequency  is used? 'Chicken wire' implies that the wavelength would need to be in the region of 50cm (if you are not to experience some loss in the reflector.
An aperture of 30m would only represent 60 wavelengths - this has a diffraction limit of about 1 degree. The pattern of the reflector couldn't just be sin(x)/x - it would need to be tailored to suppress sidelobes - just like a good radiotelescope - the lost power problem is directly equivalent to the noise performance for radio astronomy. The actual aperture would need to be considerably oversize, to allow for tailoring of the dish illumination. Remember that the vast majority of the power has to fall within the area of the receiving array.
The straits of Gib are 14km wide - that is a required beamwidth of 0.1 degrees ('Most of' the  power not 3dB points) for a 30m receiving array.

The receiving array can't be treated as an independent set of elements - they will interact and, unless you get things right, they will fail to extract all the power from the incident beam - a dipole doesn't take all the power of a passing wave.
The figures really don't seem to add up. It's, in fact, far from "simple stuff". I imagine the project needs financial support from someone - don't let it be you!

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Offline Vern

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« Reply #35 on: 12/03/2009 11:34:41 »
A few minutes with Google turned up a few articles claiming pretty high power transmission efficiencies. Much higher than I would have imagined. I think though that they are not considering all the losses; they are only measuring the efficiency at the antenna.

This link is to one of the papers

Abstract:
Quote from: the Abstract:
A new concept for solid state wireless microwave power transmission is presented. A
2.45 GHz rectenna element that was designed for over 85’%0 RF to dc power conversion
efficiency has been used to oscillate at 3.3 GIIz with an approximate 10/0 dc to RF
conversion efficiency. The RF radiation was obtained from the same circuit by supplying
the dc output with reverse polarity dc power.


The bolding of the text was my edit.
Quote from: the link
                                    I. Introduction
The rectenna is a rectifying antenna operating in a receiving mode for reception of microwave power and subsequent conversion to dc by a diode rectifier. However if an IMPATT diode is used to rectify microwave power, the same diode can also operate in the avalanche region to generate and radiate RF power in the same circuit. Thus, the circuit can convert RF to dc and vice versa but not concurrently. The polarity of the dc voltage determines the operating mode. The dc current flow is in the same direction for
either mode of operation.

Based upon the conjecture of one of the authors ( Dickinson) [4], the concept is realized using a rectenna element obtained from the JPL Goldstone microwave power transmission experiment in 1975 [5]. The Goldstone rectenna array consisted of 4,590 elements that delivered up to 34 kW of output dc power from a2.388 Ghz microwave beam. This rectenna array demonstrated an average 82.5% collection and conversion efficiency whereas selected rectenna elements were tested at a 87°/0 conversion efficiency
level [6].
« Last Edit: 12/03/2009 14:54:15 by Vern »

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lyner

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« Reply #36 on: 12/03/2009 14:16:02 »
Receiving:
The rectenna looks quite useful as a receiver. However, in the paper, their idea of using the same device to transmit seems dodgy. You would need the oscillators all to be in phase lock if a proper beam is to be produced from a n array of 4000+  coherent elements.
The idea of using klystrons and magnetrons as RF to DC convertors is also novel but I think this would be more of an 'in principle' idea rather than an 'in practice' one. God knows what electron optics would be needed to cause a beam of 'bunched' electrons  to sort themselves out and to arrive at an electrode (collector) in such a way as to get a DC  potential which is elevated above the original bias voltage.

The rectenna elements each seem to handle at least 10W and the array  deals with 34kW.  The prototype array would, presumably, have been something under 7m square so a 30m array could handle about 600kW. That sounds like quite an expensive setup for such a small power output.  And it's far from being a few bits of wire and some diodes!

Transmitting:
I don't know the maximum achievable output power for current 3GHz devices but I should think that the power available at the transmitting end would be limited to less than that unless  they used the output from several devices.

Wikkers seems to reckon that the distance of a link is limited to about a km - the antenna design starts to be a bit more  reasonable then.

As the literature suggests, this sort of system is worth considering if you are talking about a fairly remote site with low power needs, with no alternative but there are ports in Morocco which  could supply the oil for that sort of power (they already do, of course) and a 1MW generating set is a tiddler. Load balancing between countries would require a link capacity of hundreds of MW to be effective.

I did see a suggested figure of up to £13M for an undersea cable to carry power from a wind farm over distances from 10 to 30km distances.  That doesn't sound a ridiculous cost for a 2GW(!!) power link.

RF compatibility would still be an issue in a busy shipping area - even though the power density may not be lethal.

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Offline wolfekeeper

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« Reply #37 on: 12/03/2009 14:41:11 »
I can't believe that such a system could be as good as 50% efficient (and that, I'm sure, can't include the efficiency of the transmitter).
Proof by incredulity huh?

Nope, everything (DC-DC power transmission). Actually it's often over 65%, and nearly all of the losses are typically in the electronics at each end.

Quote
What frequency  is used? 'Chicken wire' implies that the wavelength would need to be in the region of 50cm (if you are not to experience some loss in the reflector.
Whatever you want, but the higher the better. 2.54 Ghz microwaves are 12cm and aren't used for other things.

Quote
An aperture of 30m would only represent 60 wavelengths - this has a diffraction limit of about 1 degree.
I haven't bothered to check it, but clearly you're out by a factor of 0.5/0.12, so the angle would be 1.2/5 * 1/360 * 2 * PI radians = 0.0042 radians. At 14000 that's 58m, so my guess of 30m was about right.

Quote
The pattern of the reflector couldn't just be sin(x)/x - it would need to be tailored to suppress sidelobes - just like a good radiotelescope - the lost power problem is directly equivalent to the noise performance for radio astronomy. The actual aperture would need to be considerably oversize, to allow for tailoring of the dish illumination.
You just build the receiver to catch as much as you can be bothered to really.
Quote
Remember that the vast majority of the power has to fall within the area of the receiving array.
The straits of Gib are 14km wide - that is a required beamwidth of 0.1 degrees ('Most of' the  power not 3dB points) for a 30m receiving array.
It's not that big; and increasing the frequency to say, 20 Ghz helps even more.
Quote
The receiving array can't be treated as an independent set of elements - they will interact and, unless you get things right, they will fail to extract all the power from the incident beam - a dipole doesn't take all the power of a passing wave.
The figures really don't seem to add up. It's, in fact, far from "simple stuff". I imagine the project needs financial support from someone - don't let it be you!
It's not so very complicated, and you seem to have plugged in an unrealistically low frequency of about 0.5 Ghz or something.

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« Reply #38 on: 12/03/2009 15:21:50 »
My assumption about frequency was based on the "chicken wire" thing.
Sorry about the "proof by incredulity" but the beamwidth needed for a 14km link is what I said - that's just 52X30/14000 degrees, if you want to get all your energy into the receive array. As I said, the 3dB width won't do or you're down to 50% efficiency for a start.

 Can you be sure of higher efficiency then 75% for a transmitter? The RF/DC conversion efficiency was claimed to be 85% (but how was that defined? - did it include the spillage from the transmitting horn or was it calculated on the basis of flux?). That's about 65% between the two.
Those figures (which are generous) were the cause of my initial incredulity. Then there is the pointing problem.

Are you really really serious when you say that you can rely on the transmitting array putting 76% of its input RF power onto an array 14km(+) away?

When you talk of increasing your operating frequency to get more directivity you have to change the devices at each end. Can you get 20GHz devices with the same efficiency as 2.5GHz devices? Also, the chicken wire idea goes straight out of the window. Your reflector will need to have 1/10 the error in its construction (+/-a quarter wavelength) and the receive array will need nearly a hundred times as many receptors.

Just one other point - did you consider atmospheric effects? Refraction is a significant issue in UHF TV reception at times; you might need to steer the beam. What do you do when it's raining 0.2dB/km loss at 20GHz for light rain.

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Offline wolfekeeper

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« Reply #39 on: 12/03/2009 15:34:07 »
There's a worked example here done by the US DOE, over 38000 km range (!)

http://www.permanent.com/p-sps-tc.htm

You're bang on about the rain effects though, that is one issue particularly on with 14km sideways possibly through thick rain; but you can partly avoid or reduce it by choosing the frequency you use, some are better than others; there's quite a lot about the basic technology and issues and solutions on that site, and the wikipedia has some as well.

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lyner

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Can you use a optical fiber for electricity?
« Reply #40 on: 12/03/2009 17:23:46 »
That link is very interesting and it deals with my (purely practical) objections.
In space, the size of an array is as big as you want; I had in mind that a huge balloon, silvered on one side (internally) could be inflated to act as the reflector.
Interestingly, they talk in terms of offshore receivers and cables to bring the power to land. I am not sure that a large array would be rugged enough for seaborne operation - we are seriously not that embarrassed for space that we couldn't find the odd few sq km somewhere in the UK.
I don't know about using flywheels up there for energy storage. Any 'massive' energy storage system would surely be better done on Earth. Batteries would maintain essential circuits during an eclipse, surely. You could even beam some power up to the satellite from Earth to keep it going. With an array as big as that, it would be easy to get power up to it when necessary using a similar system.

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Offline yor_on

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Can you use a optical fiber for electricity?
« Reply #41 on: 13/03/2009 20:41:34 »
As we are talking about electricity in general and storage of it.
How about this? Would that be possible??
http://www.physorg.com/news156011642.html

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this was done with zinc-blende-structured MnAs quantum nanomagnets.
(Manganese Arsenide?)

Here is a PDF about making and characterizing MnAs nanostructures:
http://www.nnin.org/doc/NNINreu06Toyli.pdf
« Last Edit: 14/03/2009 12:51:27 by yor_on »
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Offline wolfekeeper

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Can you use a optical fiber for electricity?
« Reply #42 on: 13/03/2009 21:18:12 »
Yeah, looks interesting.

FWIW there aren't any really stupidly significant eclipses in GEO though; the plane of the equator is angled significantly to the orbital plane, and this means that GEO sats only see eclipses for an hour or two during each of the equinoxes. There's not really any need for power storage, you just kick in your backup power supplies at those times (and you always need at least one backup anyway).

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lyner

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Can you use a optical fiber for electricity?
« Reply #43 on: 13/03/2009 22:47:07 »
But you don't need continuity of service, like a TV satellite. Storage of energy is best done on Earth for the brief times of eclipses. Merely keeping the basic circuits running up there is trivial.