Free energy from the air!

I have to admit that I’m a little wary of this.

Companies have been researching how to harvest energy from wireless data networks for many years. But it is difficult because there it is only a small amount of energy available and achieving the right level of harvesting efficiency has been the issue – up until now.

With Freevolt, we have created something special. For the first time, we have solved the problem of harvesting usable energy from a small RF signal.

I agree that there’s energy in an RF signal and I’ve no doubt that some portion of it can be captured.

But someone selling a dev kit at a price to be announced has those spidey senses tingling a bit.

And I’m deeply unconvinced (although willing to be proven wrong) that there’s going to be useful amounts of energy that can be harvested.

38 thoughts on “Free energy from the air!”

  1. “I agree that there’s energy in an RF signal and I’ve no doubt that some portion of it can be captured.”
    Yep. That’s called a radio receiver. And the amplifier circuits aren’t there for fun.

  2. Oh, this technology will certainly work – I’m old enough to remember an old uncle demonstrating his “crystal set” radio to me – that old, old, early radio receiver technology based on no more than a couple of electrical components plus a crystal and a whisker. I remember being blown away at the time by the concept of picking up a crackly AM broadcast on a device with no battery and no connection to the mains, and struggling as a child to get my head around where the power was coming from. But this is not rocket science, and I could build one in minutes, and it works.

    But what I worry about – and see legal vultures circling to fix – is that the moment you have a lot of such FreeVolt devices parasitically draining the RF energy out of the ether, then you destroy the quality of signal downstream for anyone else trying to use the signal – WiFi/radio/whatever for its intended purpose. There’s no such thing as a free lunch, and this energy can only come from the transformers driving the transmitter masts – which will end up needing to upgraded to avoid listeners’ complaints.
    Better to agree a national web of transmitters broadcasting a simple but powerful sine-wave signal at a single frequency, that all these devices are tuned to, to avoid damaging more useful, complex data signals.
    (Who would pay for such remains an exercise for the reader.)

  3. And, of course, it ain’t free energy.

    Somebody has got to broadcast that.

    Okay, we are getting better at short range low-ish loss em power transmission but we’re not quite at the long range stuff yet (never mind the huge problems where the transmitter gets out of alignment with the receiver*.)

    * Close to being “the Kzinti lesson”.

  4. Oh well done for your allusion to Niven.
    Pity the SJW/planner/social worker types don’t suffer from Kzinti bravery.

  5. I heard or read some decades ago about a man who lived close to a TV mast and wired his house up in such away so that all his electrical needs could be produced by the signals the mast sent out. The problem however was that certain people received no TV signal at all. So after an investigation he was found out.

    It appears that picking up electricity from the air ways is quite possible but it could as one commentator has already mentioned lead to loss of reception so the point of doing it could be pointless.

  6. “A Freevolt enabled smoke detector for instance would never need its batteries changed to keep your family safe.”

    If this works, why haven’t the Freevolt people made one then? Why screw around with talking about it when you could go into business making a “no batteries” smoke detector and take a huge chunk of that market?

  7. Nikola Tesla demonstrated wireless electrical power a century ago: the problem came from the more commercially minded Edison (or was it Westinghouse?) who realised that wireless electricity was really good, but metering it would be very difficult. I expect the same thing applies today.

    The issue here isn’t loss of reception if somebody else receives the waves: this isn’t a constraint with radio waves, is it? The problem, as BiS has said, is that the energy in the wave is so small that capturing it and turning it into something useful requires a further input of energy. You might as well try to capture the sound waves at the side of a motorway or a waterfall: the energy levels we’re talking about are miniscule.

  8. A Freevolt enabled smoke detector for instance would never need its batteries changed to keep your family safe.

    If it’s that much of a big deal, wire one up to the mains and have a UPS battery in it.

  9. Physically, this is just an air-coupled, inefficient transformer. The transmitter is coupling electromagnetically with the receiver. And the more people that load the transformer, the more power has to be fed into it, and the more the signal downstream is attenuated, as has been already mentioned.

  10. “Better to agree a national web of transmitters broadcasting a simple but powerful sine-wave signal at a single frequency, that all these devices are tuned to, to avoid damaging more useful, complex data signals.”

    What might be better yet would be to find some big source of radiation that could be positioned up in the sky where everyone can see it. If it kept out of the spectrum used by data transmissions and used say visible light or ultraviolet it would cause no problems; it could be powered by, I don’t know, some sort of massive fusion reaction.

    I believe that we could be about half-way to having that solution permanently available in any given area. Apart from the availability issues, the main problem is that the receiving technology needs some work to be competitive with other forms of power.

  11. But but but it’s green it’s just out there you’re all fascist wreckers in the pay of Scottish Power or OffGen.

    Can I have a doctorate?

  12. Bloke in North Dorset

    Antisthenes story was told to me about the LW transmitter at Droitwich just after it went on air to illustrate a point. They tracked down the culprit by triangulating the complaints of poor reception.

    As others have said, you need a massive power source to be of any use and because power, as BiS points out followers a 1/D^2 law.

    And we’ve been doing this sort of thing for a while now with contactless payment cards like Oyster and there’s a good reason why you have to get the card close to the machine.

  13. “Physically, this is just an air-coupled, inefficient transformer. The transmitter is coupling electromagnetically with the receiver. And the more people that load the transformer, the more power has to be fed into it, and the more the signal downstream is attenuated, as has been already mentioned.”

    No,sorry abacab, that has to be bollocks. There’s plenty of things, other than radio receivers, absorb radio waves. You could put a radio transmitter inside a totally absorbing Faraday cage. Or stick it in one of the million lightyear voids between galaxies. And it wouldn’t make the slightest difference to the transmitter. It’d still output the same energy.

  14. The Laughing Cavalier

    Drayson Technologies and Drayson Technologies Europe Ltd are the vehicles of Paul, now Lord Drayson, of Powderject and NuLabour fame. Neither company appears to have filed accounts as yet.

  15. Is it possible to direct radio transmission sufficiently accurately? I’m not a signal engineer, so don’t have a clue, but it seems to me that almost all the energy transmitted will go zipping off into space or face-plant straight into the planet. This, too, would not make for an efficient energy transmission mechanism.

  16. Bloke in North Dorset

    Philip,

    Yes, you can get a reasonable amount of direction, depending on the frequency. The higher the easier.

    Above about 20GHz dished of less than 1m diameter twill work, below that the dishes start to get too big.

    Below 1GHz you need to move to large panel antennas and these only get you down to about 60 – 120 degrees. Below about 100MHz it gets very difficult, the size of the antennas being the limiting factor.

  17. Is it possible to direct radio transmission sufficiently accurately?

    Yup. You have a different aerial design for directional or planar versus omni-directional.

    Compare (although they are receivers, it is exactly the same maths) a satellite dish, a conventional broadcast TV yagi and a radio whip antenna.

  18. Lord Drayson has impressive credentials. He is a Fellow of the Royal Academy of Engineering and has a degree in production engineering, so surely he cannot be taken in by what appears to be a scam.

    Wi-fi uses the same frequency band as microwave ovens — 2450 MHz +- a few MHz. Wi-fi uses a few milliwatts of power compared to the 800W of typical microwave ovens. There is a reason why oven makers go to great lengths to ensure that ovens are well screened so that little power leaks out; the radiation will cook you just as effectively as it cooks food.. Is FreeVolt suggesting that each home sets up a 2450MHz transmitter with a power of maybe 10W to run all your Internet of Things devices. This will drive the people who claim to be sensitive to Wi-Fi nuts.

    FreeVolt claims to be patented. There is a patent dated 1969
    Rectenna

  19. There is a reason why oven makers go to great lengths to ensure that ovens are well screened so that little power leaks out; the radiation will cook you just as effectively as it cooks food..

    Interestingly, I did a wifi survey for a pub chain – one of their greatest interference problems for both the retail and the customer free access networks was damage to the door shielding on their kitchens’ industrial microwaves.

    Well below “cooking the cook” levels but enough to disrupt wifi and Bluetooth.

  20. “Lord Drayson has impressive credentials. He is a Fellow of the Royal Academy of Engineering and has a degree in production engineering, so surely he cannot be taken in by what appears to be a scam.”
    Just because a guy’s an expert poker player doesnt mean he doesnt cheat

  21. Having now read the FreeVolt white paper, they may be onto something. I was wrong when I said that you might need a transmitter dedicated to powering your Internet of Things. There may be just enough power to augment the battery life of a very low -powered device from the energy from Freeview, mobile phone masts, and WiFi, at least in central London.

    My router has a spectral scan mode where it tells me how much signal it is getting form my neighbours Wi_Fis. The strongest signal is -80 dBm which is 10e-11 Watts or 100 nano-Watts.

    Many years ago, when I lived in London, I made a crystal set. It could just about receive the Home Service on medium wave (so you can see how long ago this was). The power in the headphones must have been about 0.1 mW

  22. This is old, old stuff.
    Broadcast Power was demonstrated in the 1960s by Steed, Peel, et all in an episode of The Avengers “The Positive Negative Man”.
    Scary stuff – Steed was only saved by the rubber soles of his shoes 😉

  23. Oh, of course: receiving is just transmission and I know from experience you can receive directionally! Duh.

    I did a bit of digging, found this:
    http://digital-library.theiet.org/content/journals/10.1049/joe.2013.0126

    This research group claims to have achieved, “1 mW of power to 1 kΩ load at a distance of up to 9 km from a 150 kW transmitter”: a far cry from Freevolt’s, “Imagine a world where your device never needs to be plugged in to charge but is permanently powered from free, unused energy that is in the air around us.” That bit’s definitely over-blown marketing hype, but maybe (possibly, in the fullness of time, Rome not having been built in a day etc.) one might in due course be able to have some radio-powered weather sensors located outside that talk wirelessly to an indoors monitor (that is itself plugged in).

    As for most of the rest of it, it’s guff designed to appeal to that section of the greenies who have little understanding of science. Powering stuff from radio isn’t going to help the environment: where do they think the electricity for the radio masts comes from to start with!

  24. Anecdata (and possibly service myth) alert.

    One of HMG’s very powerful radio transmitter farms, in the middle of nowhere (Scotland, iirc), some years ago. OIC was passed over (for promotion) RAF bod, and much in to the place looking tiddly.

    One of the HF (?) transmitters was down for maintenance and OIC ordered some erks to paint the wooden fence surrounding the aerial. Erks reported back that fence was rotten and paint was insufficient. OIC ordered them to replace it with some spare chain link fence available from some other project.

    Fence was installed and painted white.

    Shortly after re-starting the transmitter, load was seen to be rather high* and nobody could see the signal. Very shortly thereafter, the white paint on the chain link turned a rather nasty brown …

    It would be nice to think that OIC learned a lesson from this but, having met people like that (of all three services), I very much doubt it.

    * BiS isn’t quite right, above. A higher return ground path will affect a radio transmitter – you start being unable to supply enough current to maintain the voltage. Admittedly, the effect is absolutely minimal in most practical cases (especially compared to the changes in the transmission lobes for the low resistivity path to earth you create – but in the chain link example above or in his Faraday cage, the coupling would be sufficient to affect the amplifier characteristics.)

  25. No,sorry abacab, that has to be bollocks. There’s plenty of things, other than radio receivers, absorb radio waves. You could put a radio transmitter inside a totally absorbing Faraday cage. Or stick it in one of the million lightyear voids between galaxies. And it wouldn’t make the slightest difference to the transmitter. It’d still output the same energy.

    An antenna is just a conductor hanging in the air and connected to a voltage source. The voltage on the conductor varies with respect to ground (the earth).

    If you put a DC voltage on the conductor, nothing will happen, and no current will be drawn, since the resistivity of dry air is to all intents and purposes infinite. Even if the air is wet, it’s not all that high.

    As soon as we oscillate at interesting frequencies, we get the electromagnetic coupling I referred to. The coupling into deep space – of course that won’t affect the transmitter, since the couping is infinitessimal. The transmitter will couple with anything conductive – the ground, trees (particularly when wet), cars, people, whatever. If any of these draws significant power from the transmitter, it behaves exactly in the same way as a transformer. In most cases, the coupling isn’t too great.

    But put a nice earthed chain link fence right up close to the transmitter like in Surrupticious’s anecdata, or a faraday cage around it and the effect is significant, and you’ll try to draw more power than your power amp can supply.

  26. A quick glance at wikipedia (https://en.wikipedia.org/wiki/DBm) puts some upper limits on the amount of energy harvestable. For instance, Maximum received signal power of [a] wireless network (802.11 variants) is listed as 100 microwatts.
    So, if you found a place where the wi-fi signal was fully maxed out, and you put up one of these widgets, you’d get 0.0001 W of power (if it’s an impossible 100% efficient).

    My cell phone has a 2800 mAh Li-ion battery; at 3.5V, that’s 9.8 Watt-hours of energy. That means it would take a ‘bit’ over a decade (11 years, roughly) to charge my cell phone.

    It would take about 4,000 times higher collection rate to charge my phone in less than a day.

    So, from any practical viewpoint, you’re not harvesting any viable amounts of power for most things. There are a few exceptions for some ‘remote sensing’ widgets that can run on extremely low power levels (RFID tags are a very simple example), but there simply isn’t enough energy density in the RF spectrum to harvest any appreciable power.

    Another obvious thing to compare it to is solar power – it is hopefully clear that there has to be much, much less RF energy generated by us than what the sun puts out as light; therefore any RF energy harvester is going to have to be much, much bigger than a comparable sized photovoltaic system.

  27. @abacab: Antennas have a ‘near field’ region and a ‘far field’ region. Structures within the near field region will affect the radiation pattern from the antenna, and its impedance as seen from the transmitter. Generally speaking, structures in the far field have no effect. The changeover from near to far is in the order of a few wavelengths. As for abstracting power from EM radiation, it’s an incredibly inefficient process, so there is absolutely no point in setting up a 10W transmitter in the middle of your house to power ‘Internet-of-Things’ thingies.

    In the far field the attenuation is an inverse function of both frequency squared and distance squared. So crystal sets working at around 1MHz could abstract enough power (with a long enough antenna) from the signal to drive headphones. That’s an abiding memory of childhood – building a crystal set with my dad & then listening in bed to a serialisation of Lorna Doone on the Home Service. No way could that be done from FM radio signals at 100MHz

  28. Fascinating stuff, but if the amount of energy in the aether was enough to charge a phone, presumably it would be enough to fry your brain, or at least raise its temperature ?

  29. There’s a much more practical solution with a similar approach: power your stuff with a solar panel, which gets its light from a light bulb in the ceiling.

    That will be a few orders of magnitude more efficient than harvesting wifi.

  30. Bloke in Costa Rica

    I’m going to stick my neck out say unequivocally: this is purest shite. The problems are legion, and have been mostly covered here. The biggest problem is power density. If you have one bar on your mobile signal the received power is of the order of femtowatts (-113 dBm). Integrate that for twenty-one years and you get the kinetic energy of a falling snowflake.

    If you capture all the power coming out of a typical macrocell base station (which are the highest power transmitters) at 100% efficiency you will be getting about 100W (at 10 antennas × 10W per antenna). Of course no-one will get any reception ‘cos you’ve eaten all the signal.

    There’s an interesting section in Horowitz and Hill’s Art of Electronics on micropower devices. You can do some useful things with stray power but generally nothing really earth shattering.

  31. So Much For Subtlety

    gareth – “This is old, old stuff. Broadcast Power was demonstrated in the 1960s by Steed, Peel, et all in an episode of The Avengers “The Positive Negative Man”. Scary stuff – Steed was only saved by the rubber soles of his shoes”

    Now that is a classy reference. Full marks.

    It is old old stuff. So old I dimly remember that laws were passed in the 1920s or 30s to specifically ban people trying to harvest power from radio broadcasts. It is, I am pretty sure, actually an offense to put up any sort of device that collects energy from broadcasts.

  32. Been a long time since I had any dealings with RF, but as I recall, signal strength is measured in dbF, which is a decibel scale which relates received power to a femtowatt. That’s 1/(1 followed by 15 zeroes) watt. To get any really useful amount of power you’d just about have to capture the full output of any wifi transmitter, which would make you pretty unpopular with the owner of the network.

  33. Another little problem is that given the tiny power source this would provide, you’re not to be charging any batteries with it. Resistance in the charging circuit and the battery is going to kill it, and you’ll find you’ve just built the world’s teensiest heater. I had to laugh at the suggestion that a camera could be powered off it. No fucking way.

    Aside from sheer impracticality/impossibilty of the concept, two red flags:
    1. No technical data at all. If you want me to take a claim like that seriously as an engineer/hardware integrator, give me some numbers.
    2. “Perpetual Power(TM)”. You’ve trademarked that? Sheesh.

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