Energy harvesting. The legal poop.  - Page 1
Forum section: electronics / projects

author: calexanian
author_rank: Super Contributor
timestamp: October 21, 2015, 08:21:02 pm
content: Hearing a few threads on energy harvesting made me think of a interesting case study that was going around while I was in college. A property owner in the desert had power lines running through his property for a considerable distance. well over a mile if memory serves me. He decided to lay a conductor along the ground under this power line and the return the loop back some distance father away. Remember induced current drops off logarithmically with distance, therefore requiring distance from the collecting conductor to the return loop. He then used this harvested energy what was apparently enough to run his residence from with some inventive engineering. Everything was fine until he boasted a little too much about his system. THe utility came after him and he claimed that he was allowed to harvest this radiated energy hitting his property, however somebody a little more intelligent at the utility company realized that the loss of power over this section of line could be measured as a net impedance via inductive coupling over that section and the tests were performed and the man was found to be stealing power effectively.Obviously to us old timers here we see what is happening. This gentleman did not understand the difference between radiated power and inductive coupling. Inductive coupling will actually load down a source circuit in a way that can be measured as a increase in power draw of said source. Harvesting radiated power is capturing power from a transmission source and the power draw of that source is largely unaffected by whatever is receiving that power.Just something to think about when you plan your next "Energy Harvesting" project

author: calzap
author_rank: Frequent Contributor
timestamp: October 21, 2015, 09:07:52 pm
content: You make an interesting point. A list of examples where harvesting would or would not increase energy consumption or utilization at the source might be useful. Your example of power lines is an example of where harvesting would increase consumption at the source. An example where it would not increase consumption at the source would be harvesting waves emitted from a wireless transmitter antenna (in most cases). There may be some gray areas too. Other examples?Mike in California

author: helius
author_rank: Super Contributor
timestamp: October 21, 2015, 09:21:23 pm
content: Isn't it just the same old near-field, far-field topic? In general, energy density in the far-field will be low.

author: calexanian
author_rank: Super Contributor
timestamp: October 21, 2015, 10:38:55 pm
content: Quote from: helius on October 21, 2015, 09:21:23 pmMore like relationship of source and sink. Does the sink affect the source. That is known as coupling, in this case inductive. It could also be pure magnetic, kinetically, thermally, etc. Does the sink not effect the source directly. That would be captive harvesting such as radiative (Solar, radio waves*, wind, etc)I hold off on radio transmission because what some people consider capturing radiated energy is actually just complex coupling and can effect conditions in the transmitter.The distance of source to sink is not relevant in this particular situation, apart from the little matter of efficiency.

author: bitseeker
author_rank: Super Contributor
timestamp: October 21, 2015, 11:55:49 pm
content: I keep hearing about harvesting, but haven't dug deeply into it. How you harvest is certainly an important consideration. So, besides the common solar (electric & thermal), geothermal, wind, and hydro, what are "proper" harvesting methods where the sink doesn't affect the source (too much)?

author: amyk
author_rank: Super Contributor
timestamp: October 22, 2015, 04:06:17 am
content: Quote from: calexanian on October 21, 2015, 10:38:55 pmAre you implying that the operators of a broadcast radio transmitter can theoretically determine how many are "listening"?

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:52:59 am
content: Nothing of the sort. We are strictly speaking about energy consumption. In simple terms a radio transmitter puts out a specific amount of power regardless of how many receivers there are. They are independent of one another. Likewise the sun does not care how many solar panels there are. It still radiates the same amount of energy. A gasoline engine however must consume more fuel as more loads or greater loads are added or A wall receptacle with nothing plugged into it delivers no power and does not effect the generation source, but plugging a light bulb into it does. plugging that same light bulb into a solar panel does not have any direct effect on the sun, however the sun may have its feelings hurt from the lousy free loader light bulb, but thats a different topic O0

author: bitseeker
author_rank: Super Contributor
timestamp: October 22, 2015, 06:18:53 am
content: With the gasoline engine, though, if one were to harvest thermal energy from it, then that would be akin to solar. It's radiant energy that is produced anyway, independent of the harvester.What are good sources for "safe" harvesting? I've heard about scavenging radio waves, but the amount of energy is in microwatts, which is OK for running occasional low-powered things for brief moments such as remote sensors.

author: SteveLy
author_rank: Regular Contributor
timestamp: October 22, 2015, 07:51:45 am
content: QuoteIn a steady-state setup like that, there is no real difference between tapping into radiated power and inductive coupling to the source. It's only a matter of degree: if the ratio of harvested to transmitted power is small enough, there will be negligible impact on the source and one might call it harvesting "free" energy as opposed to "stealing" energy. But physically it's the same thing.

author: akis
author_rank: Frequent Contributor
timestamp: October 22, 2015, 08:24:28 am
content: Apparently heat fabours water electrolysis, I wonder if you had a combustion engine running off hydrogen produced by electrolysis, with the water circulating and absorbing the heat of the engine block, thus getting heated and helping with the electrolysis (positive feedback). It may not be 101% efficient, but it may just be so you'd only need to charge the batteries once a week rather than once a day. I am talking completely without any numbers of course.

author: BravoV
author_rank: Super Contributor
timestamp: October 22, 2015, 08:25:32 am
content: Quote from: calexanian on October 21, 2015, 08:21:02 pmCMIIW, isnt this like sneaking in a rogue "secondary" winding like transformer does ?

author: SteveLy
author_rank: Regular Contributor
timestamp: October 22, 2015, 10:21:09 am
content: Quote from: BravoV on October 22, 2015, 08:25:32 amYep. And that's how practically all*wireless power works, from wireless phone chargers to magical free-energy-fairy harvesters. You put a coil in a time-varying EM field and you'll get a voltage out according to Faraday's law.The limit to the power you can get that way is trickier to calculate but energy conservation, i.e., power-in >= power-out, along with inverse square law for a localised source, or inverse linear law for a line source will tell you what to reasonably expect. Tesla, smart as he was, seems to have forgotten about that bit when he wanted to wirelessly power the world. But maybe he did not forget and just did not care about efficiency (which is fair enough given the foreseeable energy requirement per person in his time and the promises of new technologies like nuclear ...).(*One could argue that solar is wireless power too, but quantum effects are at play there and classical EM theory breaks down, so we don't normally call it "wireless power". That term is reserved for classical EM stuff.)

author: SteveLy
author_rank: Regular Contributor
timestamp: October 22, 2015, 10:52:30 am
content: Quote from: akis on October 22, 2015, 08:24:28 amIf the engine is only 1/7 = 0.14% efficient (not unreasonable for internal combustion) and the energy recovery system is 100% efficient then you'd get one week vs one day as you say. But to make a recovery system for an inefficient engine is a lot harder than to make an efficient engine in the first place. And if a good engineer had a workable idea for such a thing, they'd incorporate it into the design of the engine itself.You do need to do some numbers to check if an idea is feasible. Dave does not do this often enough on EEVBlog/youtube, but when he does he's very good at it: back of the envelope feasibility calculations. He did a stellar job in his RF free energy harvester and solar roadways videos. They are worth watching just as training in how to think on your feet...

author: Kalvin
author_rank: Super Contributor
timestamp: October 22, 2015, 11:31:14 am
content: Metal cattle fences or metalllic surface mounted watering tubes are not allowed near the power lines?

author: VK5RC
author_rank: Unknown
timestamp: October 22, 2015, 11:40:15 am
content: @Kalvin, I think they are legal but if you draw power from them, they in turn draw more power from the power lines, again like a transformer secondary but very loosely coupled.

author: Fungus
author_rank: Super Contributor
timestamp: October 22, 2015, 12:51:18 pm
content: Quote from: Kalvin on October 22, 2015, 11:31:14 amThe trick to doing stuff like this isn't in fancy/sneaky engineering, it's simply to STFU.

author: calzap
author_rank: Frequent Contributor
timestamp: October 22, 2015, 02:58:19 pm
content: All sorts of stealth methods could be tried under high voltage lines. Consider electric fences. They can be 2 m high and have as many as seven parallel wires on insulators. The wires run to their power source which can be a km or more away, well out of the power company's easement. Not sure the power company could determine whether the fence is sucking away power from the lines without tampering with it. Maybe by flux measurements between the fence and the power lines? Could this arrangement really supply significant power to the farmer?Mike in California

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 03:16:59 pm
content: Quote from: calexanian on October 21, 2015, 08:21:02 pmI don't understand the point you are making. Obviously there's no radiated power at 60Hz. Also, no one has ever been prosecuted for stealing power by inductive coupling. The whole thing is an engineering urban legend.

author: mark03
author_rank: Frequent Contributor
timestamp: October 22, 2015, 03:37:19 pm
content: I was just pondering this the other day, and wondering if it is technically feasible to power a sensor node from proximity to an  power line. The desert story sounds like an urban myth, but the potential to harvest microwatts from a smaller loop area, like 1 or 0.1 m^2, is far more interesting IMO. Anyone care to put numbers on this?

author: Fungus
author_rank: Super Contributor
timestamp: October 22, 2015, 03:58:56 pm
content: Quote from: edavid on October 22, 2015, 03:16:59 pm

author: calzap
author_rank: Frequent Contributor
timestamp: October 22, 2015, 04:09:20 pm
content: Quote from: edavid on October 22, 2015, 03:16:59 pmOh, lots of power can be radiated at 60 Hz. Enough to kill linemen touching disconnected wires near high voltage lines. Seehttp://powerlineman.com/lforum/archive/index.php/t-11120.html.Mike in California

author: helius
author_rank: Super Contributor
timestamp: October 22, 2015, 04:10:43 pm
content: The fluoro lights underneath HT wires are taking power from the wire's capacitance, not radiated energy. If you stand beside them, they flicker off, even though your body does not block any EM waves.(Fast-forward to 5m0s, the forum code here doesn't understand embedded videos with time pointers)

author: free_electron
author_rank: Super Contributor
timestamp: October 22, 2015, 04:22:34 pm
content: Take a VF tube ( vacuum fluorescent tube ) and go stand under a power line... it will light upIs it radiated or induced ? the tube is not a loop. it only has two 'antenna's ...now , put an array of VF tubes under power lines. under the tubes put a solar panel so the light coming form the tubes produces electricityprepare to grit your legal teeth on that one ....

author: helius
author_rank: Super Contributor
timestamp: October 22, 2015, 04:29:58 pm
content: Quote from: free_electron on October 22, 2015, 04:22:34 pmThat's an even worse idea than Solar Fucking Roadways. You'd be lucky to get microwatts, since the lamps are so dim they are only visible at night (see the video)

author: penfold
author_rank: Frequent Contributor
timestamp: October 22, 2015, 04:48:33 pm
content: No gritting necessary, its still coupled in the system, and by the time you'd built collected enough tubes and panels (lets just assume they don't cost anything to give this idea a chance) you'd be introducing a very noticeable leakage.

author: langwadt
author_rank: Super Contributor
timestamp: October 22, 2015, 04:56:20 pm
content: Quote from: calexanian on October 22, 2015, 05:52:59 ambut a solar panel has an effect on what that is behind it that is now in shadow

author: Gyro
author_rank: Super Contributor
timestamp: October 22, 2015, 04:57:46 pm
content: QuoteSurely an electric fence or whatever will just be intercepting capacitive loss between the lowest conductor and ground. Hard to see how that would be detectable, or indeed actually pulling extra power from the line - just diverting the power loss that is already there.

author: @rt
author_rank: Super Contributor
timestamp: October 22, 2015, 04:58:27 pm
content: What if you modulated the coil frequency with several lower frequencies,and each customer was supplied with a different lower frequency LC circuit for their receiver?Could you then meter their magic power?What about giving each customer an LC receiver of an harmonic of the carrier that was further awayfrom the fundamental the closer they are to the coil?Could that be detected on a 1920’s steam powered oscilloscope?

author: Tom45
author_rank: Frequent Contributor
timestamp: October 22, 2015, 05:13:00 pm
content: This thread reminds me of a related issue.Back in the 50s or 60s, new very high voltage lines went in through eastern Oregon to carry Columbia River hydropower to California. Eastern Oregon is mainly desert with a very low population density.A farmer whose land had one of the new lines crossing it started complaining that any time he drove his tractor too close to the power line, the tractor would just quit. Apparently the power line's field was too much for the tractor's ignition system.The power company solved the problem by buying him a diesel tractor.

author: akis
author_rank: Frequent Contributor
timestamp: October 22, 2015, 05:13:49 pm
content: Quote from: edavid on October 22, 2015, 03:16:59 pm60Hz? I had thought it was in the KHz region over tranmission lines. I have not bothered to google it.

author: SeanB
author_rank: Super Contributor
timestamp: October 22, 2015, 05:21:30 pm
content: Pulling energy out of a radio transmitter field shows up as field changes in the monitoring points the radio station is required to set up and record, so they would notice the power draw. There was a German farmer pre war who set up a dipole antenna in his milk shed, which was close to the transmitter, and he ran the lights off the centre of the dipole. the radio station engineers did notice the drop in field strength, and mapped it, leading them to the shed. If he had just had the right length of fence doing the same they would have fixed the problem by putting in at no cost some eggcup insulators to detune it, but here he was charged with "theft of electricity" and had the lights removed along with a fine.

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 05:26:50 pm
content: Quote from: calzap on October 22, 2015, 04:09:20 pmYou seem to be referring to induction, not (electromagnetic) radiation. As far as I can tell, the whole point of the OP's post was to distinguish between the two. As I said, there is no radiation at 60Hz.

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 05:28:29 pm
content: Quote from: akis on October 22, 2015, 05:13:49 pmOf course not, the losses would be excessive. It's either line frequency or DC.

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 05:29:21 pm
content: Quote from: SeanB on October 22, 2015, 05:21:30 pmDoes anyone believe these stories?

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:49:33 pm
content: Quote from: BravoV on October 22, 2015, 08:25:32 amIt is just like that.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:51:32 pm
content: Quote from: Kalvin on October 22, 2015, 11:31:14 amActually cattle ranchers will not run metallic ungrounded fencing generally along power lines because cattle are some of the most sensitive animals to electric shock.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:52:48 pm
content: Quote from: VK5RC on October 22, 2015, 11:40:15 amAnd in the extreme somebody could measure that additional draw on the source and claim whoever is causing them to draw more owes them for that energy. Of course this is an extreme case.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:55:32 pm
content: Quote from: mark03 on October 22, 2015, 03:37:19 pmIt is not a myth. Induced current is actually a very real problem in some instances. Also there is capacitive coupling. It is so much of a risk as a matter of fact that utility companies have grounding rules for working on lines near other energized lines and people have died from it in the past.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:57:47 pm
content: Quote from: free_electron on October 22, 2015, 04:22:34 pmIf they are high tension lines the phosphor will fluoresce from secondary break down from the radiation. Pretty neat stuff actually.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 05:58:57 pm
content: Quote from: langwadt on October 22, 2015, 04:56:20 pmVery true. COnservation of energy and mass is still in full effect last time I checked. O0

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 06:00:02 pm
content: Quote from: @rt on October 22, 2015, 04:58:27 pmIt depends. Is that scope powered from wet steam or super heated dry steal? O0

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 06:02:07 pm
content: Quote from: SeanB on October 22, 2015, 05:21:30 pmThis is why i used a * next to radio waves as a caveat. Any ham radio operator can tell you how near field objects can change the loading and coupling of a transmitter.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 06:04:46 pm
content: Quote from: Tom45 on October 22, 2015, 05:13:00 pmI have a recently departed friend who worked on that system. It was actually a DC current system originally with a giant bank of thyratrons (Which he helped design) and a giant filter at the other end in synchro 3 phase switching at 60hz into a giant filter to get the sine wave back.

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 06:05:36 pm
content: Quote from: edavid on October 22, 2015, 05:26:50 pmCorrect.

author: akis
author_rank: Frequent Contributor
timestamp: October 22, 2015, 06:15:20 pm
content: You are right it is not the frequency that increass it is the voltage, they are in the 100s of KV. I am not sure if this was mentioned anywhere on this thread. And that voltage is wrt ground.

author: mark03
author_rank: Frequent Contributor
timestamp: October 22, 2015, 08:42:25 pm
content: Quote from: calexanian on October 22, 2015, 05:55:32 pmSo you know the guy in the story, eh?It takes very little energy to electrocute someone under the right conditions. Running one's house off this energy is the part I remain skeptical of.But whatever. I still think my question is more interesting. How much power *can* you extract from a typical AC line, near ground level, within a bounded area/volume? Microwatts, milliwatts, ?

author: calzap
author_rank: Frequent Contributor
timestamp: October 22, 2015, 09:34:53 pm
content: Quote from: edavid on October 22, 2015, 05:26:50 pmSo to be clear, a time-varying magnetic or electric field is not considered radiation as long as no photons are involved. Correct?Mike in California

author: mark03
author_rank: Frequent Contributor
timestamp: October 22, 2015, 09:58:23 pm
content: Quote from: calzap on October 22, 2015, 09:34:53 pmWhat's the cutoff frequency below which it's no longer photons, just E and H fields?

author: calexanian
author_rank: Super Contributor
timestamp: October 22, 2015, 10:04:26 pm
content: Quote from: calzap on October 22, 2015, 09:34:53 pmOh. good question I had not previously thought of. think of the nature of magnetic lines of force VS. radiated energy via either wave or particle emission. all can be expressed on the EM spectrum but all behave in completely different ways.This is the direction I was hoping the thread would go.

author: akis
author_rank: Frequent Contributor
timestamp: October 22, 2015, 10:07:52 pm
content: Quote from: mark03 on October 22, 2015, 08:42:25 pmI just read on wikipedia that there can be from 100s of volts to 100s of KV on those overhead lines, depending.

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 10:28:59 pm
content: Quote from: calzap on October 22, 2015, 09:34:53 pmCorrect!

author: edavid
author_rank: Super Contributor
timestamp: October 22, 2015, 10:33:43 pm
content: Quote from: DiligentMinds.com on October 22, 2015, 10:09:07 pmAgain, do people really believe these stories?http://www.snopes.com/politics/crime/rainwater.asphttp://www.enlight-inc.com/blog/?p=1036#floridas

author: akis
author_rank: Frequent Contributor
timestamp: October 23, 2015, 07:28:15 am
content: Quote from: edavid on October 22, 2015, 10:33:43 pmAs far as I know in the UK you can collect rainwater and do what you like. What you should not do is to return it to the sewers because then you are loading the sweage system with more water than the Water company had originally provided. Of course even if you did this it would be the Water company that might sue you, not the state.In the first article above it is clear in the US collecting rainwater is dodgy at best, although this could be limited to altering of natually occuring streams and rivers - I am sure there will be similar lawa in the UK.It is not clear what would happen if he had created his "pools" using only rainwater theat fell on his own land.