Slashdot Mirror
Focused Microwaves Could Enable Wireless Power Transfer
esocid alerts us to news out of the University of Michigan, where physics researchers have found a way to focus microwaves to a point 20 times smaller than their wavelength using a new 'superlens'. Such resolution was thought to be impossible until recent years, and it could bring about the capability to transfer power wirelessly.
"No matter how powerful a conventional lens, it cannot focus light down to more than about half its wavelength, the 'diffraction limit'. This limits the amount of data that can be stored on a CD, and the size of features on computer chips. The new lens is a 127-micrometer-thick plate of teflon and ceramic with a copper topping. 'The beauty of these is that they're planar,' Grbic says, 'they're easy to fabricate.' The lenses can be made through a single step of photolithography, the process used to etch computer chips."
While it's nifty that they can focus EM radiation to a smaller point now, I'm not following how this will enable wireless power transfer.
Do you think perhaps that the power levels we are discussing here are somewhat lower? Just maybe things take less power these days? Rectennas were meant to deliver grid-power rectified from microwave masers in orbit... I think here we are talking about a few mW to power a gizmo. Sheez.
Firstly, it's horribly inefficient. There are significant losses over the signal path that hand waving won't make go away. And then there's the real show-stopper: high power microwave beams would be a hazard to aviation, shipping, or anything or anyone else who got in the way.
There'd be enough scattering of the beam to spread the danger around. Sure, this technology is possible - but there just don't seem to be any practical applications for it. Wire is much more efficient and airmen have a chance to see and avoid it. They'd never know that microwave beam was there until they entered it.
Beaming power in from space is a perennial favorite - but nobody ever seems to be able to get around the atmospheric effects. And I'd prefer to not have any randomly scattered ionizing radiation impinging on my home, thanks.
Depends on how much the power is needed, and how soon. The space elevator seems like it's a long time away, still in need of new materials to be invented, and so on. On the other hand, solar power in space is feasible now, at least technically.
Without power people die. So the risks of catastrophic failure of microwave power transmission from space, must be weighted against the possibility of many people not getting electricity. It might be safer to build powerplants now, than to wait for a hypothetical space elevator.
I don't know if he's correct, but even a small amount of thought should show you a lot of possible ways.
* No exposure to the elements, thus reduced maintenance cost from wind/weeds/corrosion
* No land cost
* No clouds, no day/night cycle
* Cost is based on weight, not on land, potentially allowing for use of extremely large light cheap panels instead of smaller denser more expensive ones
Does it make up for the difference? I couldn't say. But there's four ways in which space beats land in terms of efficiency.
Breaking Into the Industry - A development log about starting a game studio.
Actually, NASA's study got it exactly right. The amount of solar-collecting material you'd need to place into orbit is large enough that you'd spend a lot more energy and money getting it into orbit then you'd ever get back from it once it was functional. Things may have improved since then (more efficient rockets, lighter solar panels, etc), but I doubt they've improved so much as to make the plane feasible yet. I'd re-do the feasibility studies after the space elevator is up and working, getting enough mass into orbit will be a lot cheaper then
I don't care if it's 90,000 hectares. That lake was not my doing.
No, the problem is that carbon dioxide is acting as a blanket, trapping too much heat beneath it.
How is adding more energy to the equation going to do anything but make it worse?
It's not a heat beam, it's a microwave beam. There's a big difference between the two. The amount of heat generated by the beam when it reaches the receiver would be insignificant, and it would generate no heat when going through the atmosphere, because the wavelength chosen would be one that is transparent with respect to air. So the net effect would be practically zero added heat. (Even if you count the heat generated by the motors powered by the resulting electricity, it's still insignificant compared to the heat trapped by CO2 in the atmosphere) And if we use that device to replace traditional fossil fuels, then its net effect would be a significant reduction in CO2 output.
There are good reasons why in-orbit solar power isn't a good idea at this time, but your reason isn't one of them.
I don't care if it's 90,000 hectares. That lake was not my doing.
No. The total world energy consumption is roughly 15 TW per year. In comparison, the total solar energy striking the Earth is just over 150,000 TW. Therefore, replacing our entire energy consumption with external sources only increases the energy flux striking the Earth by about 0.01%.
Three points. :)
First off, geosynchronous may or may not be a good idea. Geosynchronous orbit is painfully expensive, and in most cases it's far more cost-effective to launch a large number of low-orbit satellites. If receiver stations were placed in various locations, satellites could just lock on to a different receiver as they pass over the globe. (On top of this, it means that a lot of different countries could theoretically buy energy at various times from this - it might even be worth placing receiver stations in third-world countries, since it's not like the power would be doing anything useful if it wasn't getting sold.)
Second, space is really really big. Even with the space junk we have up there already, impacts are spectacularly rare. It's a factor, but it's not a huge factor.
Third, why fix the broken panels? I highly suspect it would turn out to be cheaper to simply launch more satellites, at least until we have some kind of orbital repair bots. As long as the core electronics are reasonably redundant, the thing can stay up there as long as it's got a single working panel.
Breaking Into the Industry - A development log about starting a game studio.
Are you serious? You're smarter than a Nasa study?
I don't claim to be (though I did work on NASA projects and have some idea where I stand among the mind power of the rocket science community B-) ).
But I'm not talking from my own work. I'm summarizing what I heard from some of the braniacs who were paying attention to the problem.
Then you can certainly explain how 1300 watts per square meter and putting it...IN FUCKING OUTERSPACE...is better than 1000 watts per m^2 on the ground.
Well for starters:
- No clouds, rain, or snow.
- No atmospheric attenuation.
- No night.
- No seasons. ("It's always noon on midsummer's day.")
Those are good for about a factor of seven (depending on the earthbound site you're comparing).
More importantly:
- No gravity (except tides).
- No wind (except solar wind).
- No oxidizing atmosphere.
- No corroding water and waterborne ions.
This enormously reduces the structures required.
That would be an enormous reduction in the amount of material needed to make and mount solar panels. Most of their structure is to protect them from the elements and support them against gravity and wind.
But we're not talking photovoltaic solar panels here. We're talking a steam plant, with the steam generated in pipes and mirrors and condensed by pipes with black cooling fins in the mirrors' shade.
With no gravity, wind, and the like, building square miles of parabolic-cylinder solar mirrors is trivial. Making them of aluminized mylar "spaceblanket" material supported by glued-together toothpicks and cobwebs would be a massive overdesign. Virtually all of your mass is the boiler and condenser pipes and the wisp of structure that keeps them straight and properly arranged and oriented as they heat and cool unevenly.
Now it might prove even better to build some film solar panels - especially if you're doing it in space by vacuum deposition of films on some flimsy substrate with an unlimited supply of hard vacuum for free. But sending up bundles of pipe, rolls of wispy plastic, and a flimsy support structure to expand in space. wrap with the mirror film, and aluminize once it's in place is a well understood and (as space stuff goes) inexpensive process.
The power plant is a moderately small lump of machinery suitable for assembling in orbit and charging with a small amount of water.
The transmitter array gets deployed much like the mirrors - but more simply. (It doesn't have to be accurately, or even consistently, spaced. The transmitters are synchronized and the array is focussed by a pilot beam from the ground site, computing the complex-conjugate of the incoming carrier's waveform to focus the beam on the antenna surrounding the pilot transmitter. Lose the pilot and they go incoherent - spreading the energy about equally through the surrounding sky, of which the entire facing side of Earth is a small fraction. (And you can modulate the pilot with an encrypted spectrum-spreader so nobody can steal the power or redirect it to another target.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
... replacing our entire energy consumption with external sources only increases the energy flux striking the Earth by about 0.01%.
Actually, replacing ground-generated electricity with space solar power REDUCES the heat load.
First: Ground generated electricity is made with big heat engines, limited by the carnot cycle. In addition to the heat released by using the energy, there's the heat released on the cold side of the heat engine. The total is a lot more than you bought and used.
But with space solar power the cold side of the heat engine is in space, radiating toward the sky (with it's black body temperature of 4 degrees absolute). The dumped heat misses the earth. All you heat with is the useful power and a few percent losses. (The sky-to-ground system is estimated to run in the range of 90% efficient and only part of its losses are on the ground.
But far more significant: Fuel-driven ground generators release carbon dioxide, which continuously traps solar power as heat until it's eventually scrubbed from the atmosphere decades or centuries later. That is a big multiple of the useful power actually delivered. No fuel burned on Earth, no CO2 pumping the greenhouse.
The main problem will be keeping us from sliding into an ice age over the next 400 to 1,200 years. (According to one model the current interglacial peaked at about the dawn of agriculture and we've been essentially regulating the earth's temperature as the "furnace" output has been curving down for the last 6,000 years or so, with a slight bump since industrialization. Stop the CO2 and we'd quickly crash back onto the steepening slope of the cooling curve.) But that takes decades to centuries. So we can decide what to do about it in a few generations, when we start to get below the old "regulated" temperature.
One nice thing: If we need to bring in more heat from space we'll have the infrastructure to do it. B-)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Don't forget military vulnerability. If your entire power supply is based on things that are really far away in space, you'll have a hell of a time protecting them from sabotage or outright war. In fact, in case of war, you'll need to have some kind of back-up power source that you can use to power your country for at least a few years, until you either lose and get taken over (in which case it's now someone else's problem) or the war ends peacefully and you can shoot another transmitter into space.
In that case, you have to decide which kind of terrestrial power to choose: coal, oil, solar, gas, wind, nuclear--all of which have their drawbacks. So, to an extent, you're back at square one.
He didn't say "died".
I make websites and stuff. Buy one.
Of course - it doesn't have to be a desert, just a place where it's seldom cloudy.
The transmission losses using microwave to transfer energy may make that setup unpractical anyway. And there is the health issue too. What if a solar array turns the radiation to downtown Los Angeles or other major city? Time for the greatest Darwin Award in history?
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
It's a factor because of transmission costs and because of the availability of good land for this. Good land for solar panels tends to be good land for other things as well, unless it's off in the middle of nowhere, in which case you get the giant-cable-maintenance problem again. Trying to build a solar farm next to the Bay Area, for example, would be pretty impractical, while two or three receiving stations would be a lot cheaper.
:)
My position is still that I, and most of the people in this thread, don't actually know enough to determine whether space solar makes sense
(I do agree that nuclear is hilariously underused though. Get these damn rabid Greenpeace members out of my energy generation, dammit)
Breaking Into the Industry - A development log about starting a game studio.
- Enough power to completely replace fossil fuel AND nuclear plants and absorb forseeable energy use expansion for decades.
- 'Way cheaper, too. (Even at '60s fuel prices.)
- Essentially no pollution at ground level.
- Bootstraps a space program that can then move other manufacturing processes, and THEIR pollution, off the planet as well.
I'd like to add another:
- Completely change the balance of power in the middle east by dropping a significant fraction of daily demand for oil.
Do not mock my vision of impractical footwear