RF Energy Harvesting

Whatya talkin' about, I been doin' that fer years....uh,,,,could ya hold yer arm out, yeah that's better...

There is a fair amount of energy being used to keep computers running even in safe mode, keeping TV sets in the "instant on" mode, clocks, and other tiny but persistent loads. I have seen some estimates that as much as 10 percent of the power on the "grid" is being used for just such applications. (Seems high to me, ) If that is so, then obviously it would stand to reason that if you can use the EMF in the atmosphere around the appliance to keep its clock running, or whatever, you would get the equivalent of ten percent more usefulness out of existing power plants.

I saw a radio being sold a few years ago that ran entirely on ambient emf, and the ghost chasers so beloved by reality TV shows have explored emf fluctuations rather well. It there, for us to use as we see fit.

There are many people exploring this technology. The fields of "resonant Magnetic Coupling" and and large scale Tesla type broadcast power have their problems, but those problems can be overcome with with the right engineering approach. It would take a bold engineer though, I hope you will become one of them. It is an exciting new field, and part of a very large exciting field of harvesting ambient energy. When you consider that a very large amount of energy is lost in transmission, every local source of energy, no matter how small, becomes important.

My guess is that the average stray RF energy density around is is orders of magnitude smaller than that.

Then there is the power required to run the energy harvesting electronics and perform the conversion to usable power. Seems pretty inefficient.

You don't think 6.6% percent of power plant savings is significant? Ever pay to run electrical to your farm? It runs in the region of five thousand dollars per pole plus hookup. The cost of transmission is always overlooked when talking about alternate energy. I think the future is in localized energy harvesting. Not just electrical, mind you. Solar, wind, and yes, even EMF harvesting to limit the disgracefully inefficient transmission losses.

Did you even READ the links in my article? I don't make stuff up you know.

I diod not say that. I said that the energy field densities are probably much too low to expect to harvest 10% of of your domestic energy needs.

No you did not.

But I will be charitable and assume for the moment that THAT is what you meant.

I think it would be unlikely that we could shut down one in ten coal burning power plants by simply unplugging all the cell phone chargers in the country. (What a nice thought! But yeah....maybe not so likely. But ... there may be ways to do that.) But parasitic loads are more significant than most people think. two hundred and seventy seven million wireless cell phone chargers (according to AT & T) times 170 milliwatts equals a significant load that really does not need to be there. (those are the watts which are expended AFTER the phone is charged) Then there are the "instant on" TV sets. Its, what...400 million sets, all drawing 300 mw each. Little 12 volt transformers sprouting from power bars all over the country like toadstools...all faintly warm from...oh right...parasitic loads. hundreds of millions of personal home computers which never get shut off....clocks and thermostats which should never be shut off...but they are all part of the vampire load which could be reduced by local power production. One form of local power production might well be ambient emf. I DID mention others didn't I?

I stand by my reply that clever and innovative engineering can use ambient EMF fluctuations for many things, and I suggested an application. And provided links. And even an economic incentive to do it. If it doesn't save ten percent, well shucks....at least I tried. (I resist the urge here to ask what clever idea other people came up with to reduce transmission losses and parasitic loads.)

I wonder if these sell well.. I hear they save a generous 2 cents a month, it seems like it would take a long time to pay it back! A switch or an RCA jack would be cheaper...grin!

Yusef, Looks like engineers are working on the problem:

http://www.edn.com/blog/40649-Microchip_and_Cymbet_XLP_energy_harvesting_development_kit_Energy_harvesting_application_development_kit_uses_eXtreme_low_power.php

http://www.edn.com/article/458005-Create_Wireless_Sensing_Applications_Batteries_Not_Required.php

http://www.edn.com/article/460787-Harvesting_energy_from_vibrations.php

...but I sense that it will take a very long time to recover the cost of these kits!

The power lost in transmission lines is not re-captureable by "energy harvesting". It manifests as a low grade heat distributed over the length of the transmission line due to skin effect and low grade heat in the air surrounding transmission lines due to dielectric heating. The referenced Wikipedia article is not complete or completely accurate.

Energy harvesting is a novelty, fun for a hobbyist to tinker with. Maybe you can run an LCD clock with it, maybe not. Unpowered crystal radios for local high power AM stations have been around since the turn of the century. Again, nothing more than a fun novelty.

The sad reality of energy harvesting is mostly enforced by the inverse square law. Sorry, no one has or will ever have a magical solution for that physical reality.

The reason there will not, and has not, been some "bold engineer" to solve these problems is that the engineers that understand the physics involved aren't interested because the reality is that it doesn't constitute enough energy to provide utility for much other than novelty effect. Microwatts is just microwatts. We capture them with antenna and call it radio.

Oh no, here we go again.

Utter nonsense.

What will you do with microwatts of power?

thats more or less the receive level of radio receivers.

Pico watts if youre talking cell phones.

Besides if you trap all the RF energy, no ones receivers will work.

Someone IS using the power, else it would not be transmitted

If the goal is to harvest all transmitted energy, which radiates spherically, the receiving antenna is as large as the entire volume of space the signals propagate through.

Again, utter nonsense.

I liked the voltage differential from altitude even better.

I'm a ham WB9SBD And I used to fly kites and use long wire attached to them for ntennas.

But I always had to place resistor to ground to bleed off the amount of static that would come down that wire. if I did not I usually blew out the front end of my radio, or if i touched it before it was drained, it made a electric fence joly seem like the putting your tounge on a 9 volt battery.

There was one tme it litterally threw a buddy of mine about 4 feet after getting hit by it before we learned to bleed it ll off first.

yes I'd forgot - this is a very good point!

There is ambient power in static charges from the air (clouds overhead etc) that is a reasonable amount of power (milli-watts clear day conditions, to mega-watts aka lightening!)

good point NSS

To Redfred,

Well, we all know about radio/tv/cellphone/cosmic etc radiation reaching us on earth. Unless we actually "harvest" it, most of it just gets absorbed by the earth and other sucg objects. Yes, it is very low power for most applications, but surely more efficient harvesting techniques can be discovered/developed?

To Yusef1,

Thanks for the links. Yes I see you get what I mean. Surely when we calculate the millions of stars, solar radiation and terrestrial transmitters surely we can output something greater than is currently attempted? Any thoughts?

To ss3e55: yes, to capture the complete transmitted power, you would have to cove a very huge(1) sphere, but if we had a huge forest of Rf capture bays (some what like the solar panels in California(?)), would we achieve anything?

mathewkyle,

There is one great example of a star's EM radiation raining down on earth and it can be collected - its our sun.

All other stars and emitters of all types (jupiter for instance, nebulae etc) represent a absolutely tiny amount of power. Perhaps an example will bring home the magnitudes involved...

lets assume that proxima Centura is like our sun in power output. And since its the closest star other than the sun lets see what it adds to the power we receive and compare that to the sun's power..

Call the Sun's power here on earth 1.0 - and that's our star only 8 light-minutes away.

Then consider the power of a star of the same radiated strength (forget for a minute the spectrum, absorption etc.) that arrives here from 4 light-years away.

The power from that star (Proxima Centura, symbol Ppc) will be less by the ratio of the square of the distances...we'll convert light years to light mins to be consistent...1 light year = 365.25 * 24 *60 light minutes (525,960)

Psun = 1.0 (at 8 light mins distance)

Ppc = 1.0 * (8 / (365.25 * 24 * 60)) ^2 = 1.0 * (8/525960)^2 = 1.0 * (1.521028 e-5)^2

Ppc = 2.3135 e-10

So the closest star to us adds around two ten billionths to the power falling on earth that our own Sun does. Other stars are much further away (as are galaxies and other sources) and add much much less...So if you think that say a solar array of 100 sq meters gives a reasonable power - to get the same from Proxima you would need an array of over a 1000 billion sq meters (or 1 e+12sq meters)
Earth's area is around 500 million sq km (or 5 e+8 km^2) = 5 e+14 sq meters - but only 1/2 faces any one star at one time...

In other words we'd have to cover about 1% of the earth with solar cells to collect that same power (and forget the that solar cells wouldn't even work at so low a density of received power or that the inter connection cables would lose more power than would be collected due to resistance).

Its just that the square law prevents us collecting anywhere near useful levels of power from extraterrestrial sources.

Also BTW read about Olber's paradox to see why the billions of stars "don't help" http://en.wikipedia.org/wiki/Olbers%27_paradox

ss3e55: yes, the actual figures do bring of the startling and somewhat discouraging facts. Actual received power is too low or extremely large collection areas are required. Seems we have no other way of working around this!