Results 1 to 16 of 16

Thread: Recycled Electricity?

  1. #1
    Join Date
    May 2005
    Location
    N.E.Ohio
    Posts
    22,006

    Recycled Electricity?

    I ran across this article about how a city saved money by installing some mysterious device.
    City Saves Thousands by Recycling Energy

    There's so little information about this claim on "recycling electricity" so it sounded to me like some snake oil device.
    So; I went to the company's website. Again; it sounds like snake oil.
    But there are two things that make me wonder. One is a city that's willing to provide a testimonial. The other is that they claim these devices have been in use for a long time in the industrial world.

    Because of the latter, I figured someone here might have some insight into what this is.

    All I can figure out is that maybe they just drop the voltage since the motor they demonstrate is pulling the same amps while the feed to the device is drawing less.

    If so, it sounds like a fire hazard to me.
    Plus; I don't see how they can apply the word "recycle" to the device.

  2. #2
    Join Date
    Jun 2010
    Posts
    1,686
    From the FAQ on the website, it appears that the device is doing a power factor correction: http://en.wikipedia.org/wiki/Power_factor

    I'm a bit puzzled though, because where I live (Europe), residential users are billed for active power (P), not apparent power (S), so the device would have no effect on your bills.

  3. #3
    Join Date
    May 2005
    Posts
    8,188
    There's question number one in their FAQ, says it is not effective with heat-generating devices like toasters or ovens:

    http://peakenergytech.com/faq#question1

  4. #4
    Join Date
    Sep 2005
    Posts
    564
    Quote Originally Posted by kamaz View Post
    From the FAQ on the website, it appears that the device is doing a power factor correction: http://en.wikipedia.org/wiki/Power_factor

    I'm a bit puzzled though, because where I live (Europe), residential users are billed for active power (P), not apparent power (S), so the device would have no effect on your bills.
    I agree, this is most likely "snake oil."

    Here is another clue from the article:
    “Weideman uses a sample motor in a demonstration.
    We are buying from the power company, about seven amps,” said Weideman.
    Flip on the switch that recycles the energy.
    “You can see now we’re only buying about 2 ½ amps,” said Weideman.
    One buys watts from the power company, not amps.
    Electronic filters can change the power factor for an application - this is especially true for an unloaded induction motor - most likely as used in the demonstration. (Such devices can produce small improvements in efficiency with some motors.)

    However - in this demonstration, if instead they had measured wattage use (what is actually metered and paid for) - their device would likely not show any change in actual power (watts).

    Here is a one-page summary of the issues with reactive power, power factor, and wattage - with a nice graph:
    www.motorsanddrives.com/cowern/motorterms16.html

  5. #5
    Join Date
    May 2005
    Location
    N.E.Ohio
    Posts
    22,006
    Thanks Kamaz, I guess I'll have to learn more about how power factors and induction work. But; from what I do know, it sounds like a reasonable concept. I also need to learn how apparent and actual power is metered.
    Until I learn this, I will still have the conflict that BioSci presents.
    It sounds right that the wattage is the measure and wouldn't have an effect, but I'm sure the way it's metered might come into play. Especially if the city in the article actually did realize a savings.

  6. #6
    Join Date
    Apr 2004
    Posts
    1,805
    I observe the Wikipedia article on power factor includes the comment:
    "Individual electrical customers who are charged by their utility for low power factor may install correction equipment to reduce those costs."
    So, if your utility does charge you for low power factor, then you can save money by installing correction equipment to reduce it. There is also some suggestion in the article that electrical losses are higher with a lower power factor, so there may be energy efficiency advantages also.

  7. #7
    Join Date
    Sep 2003
    Location
    Denmark
    Posts
    18,442
    Yep, this is a classical problem with electrical motors where the power measured in watt and in VA (VoltAmpere) can be very different, inductive loads can put enough skewed load on the system that the power company will charge less per watt if the consumer puts in compensators.

    Not snake oil, just a bad description written by people who don't know the difference between reactive and resistive loads.

    There's a pdf describing things from the power companies poing of view, from the US Department of Energy here
    __________________________________________________
    Reductionist and proud of it.

    Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
    Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
    A person who won't read has no advantage over one who can't read. Mark Twain

  8. #8
    Join Date
    Sep 2003
    Location
    Denmark
    Posts
    18,442
    Yep, this is a classical problem with electrical motors where the power measured in watt and in VA (VoltAmpere) can be very different, inductive loads can put enough skewed load on the system that the power company will charge less per watt if the consumer puts in compensators.

    Not snake oil, just a bad description written by people who don't know the difference between reactive and resistive loads.

    There's a pdf describing things from the power companies point of view, from the US Department of Energy here.
    __________________________________________________
    Reductionist and proud of it.

    Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
    Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
    A person who won't read has no advantage over one who can't read. Mark Twain

  9. #9
    Join Date
    Sep 2005
    Posts
    564
    The "snake oil" comes in if the company is marketing this to residences (which they apparently are) since they are (without exception?) charged for watts and not according to power factor. Also "snake oil" to characterize power factor filtering as "re-cycling".

    It also applies to their "demonstration" of "power savings" by looking at amps with an un-loaded induction motor - very deceptive and not even appropriate if a commercial establishment is being billed by power factor (commercial pumps and motors are seldom run un-loaded and the power factor improves under load).

    Any actual power savings for using this device do not occur from the reduction in actual power usage - but rather since fewer amps are moved back and forth the distribution system (power company) can save on the distribution network costs and resistive losses. The user also saves a little bit on resistive losses - but such losses are small compared to the cost savings for the utility. Which is why utilities often do incorporate power factor into the billing scheme for industrial users.

    It is unclear if the city in this example is even billed according to power factor or if the city actually had any real savings as a result of the use of the device.

  10. #10
    Join Date
    May 2009
    Posts
    457
    Actually Heathrow Airport is right now spending quite a lot of money on installing power factor correction systems for all the baggage system conveyor drives. With over 5,000 motors the saving is substantial. The saving is not just on the bill. Companies in the UK can claim large tax breaks if they can show any substantial reduction in energy usage.

  11. #11
    Join Date
    Jul 2010
    Posts
    389
    Quote Originally Posted by HenrikOlsen View Post
    Yep, this is a classical problem with electrical motors where the power measured in watt and in VA (VoltAmpere) can be very different, inductive loads can put enough skewed load on the system that the power company will charge less per watt if the consumer puts in compensators.

    Not snake oil, just a bad description written by people who don't know the difference between reactive and resistive loads.
    Yes, the problem stems from the phase shift you get from inductive and capacitive loads. (but not resistive loads)
    Since a motor is an inductive load, it phase shifts the AC waveform with respect to the grid (obviously not good :-) )

    Back in the 80s when I worked at a factory, we used to have capacitors installed to offset the inductive load of all the motors on the factory floor.
    (-since capacitors phase shift in the opposite direction to coils)
    This is probably done by power electronics these days..

    Peter

    PS
    Actully, I think 'recycled electricity' is ok. The capacitors do this by working like batteries, charging and discharging 50 times per second.
    Last edited by baskerbosse; 2011-Sep-28 at 11:32 PM. Reason: Added PS

  12. #12
    Join Date
    Sep 2005
    Posts
    564
    Quote Originally Posted by RAF_Blackace View Post
    Actually Heathrow Airport is right now spending quite a lot of money on installing power factor correction systems for all the baggage system conveyor drives. With over 5,000 motors the saving is substantial. The saving is not just on the bill. Companies in the UK can claim large tax breaks if they can show any substantial reduction in energy usage.
    Yes, industrial users with high percentage of power used by motors can see significant improvements in the effectiveness of power distribution and regulation by using power factor correction systems. Such systems do not significantly reduce the actual power (watts) used by individual motors but do reduce the excess movement of power back and forth and can reduce costs to supply and manage the power usage at the site.

    Such savings are not realized by small users (residences) since their power fees are based on actual wattage. The utility or overall power distribution system may benefit from installation of power factor correction at smaller usage sites (to the extent that such users have a low power factor) but unless such users have a rate schedule that has a power factor penalty, just changing the power factor does not reduce the actual power used (watts) or the user's power bill.

  13. #13
    Join Date
    May 2009
    Posts
    457
    Quote Originally Posted by BioSci View Post

    One buys watts from the power company, not amps[/url]
    The two are related, after all Watts = Volts X Amps. If there is a reduction in amps, how can there not be a reduction in watts ?

  14. #14
    Join Date
    Sep 2005
    Posts
    9,031
    In AC systems, real power, measured in watts goes as VI*cosO, where O is the phase angle. Cos O is thus the power factor. One can also construct a notion of power factor for harmonics as well. Indeed, consider the design of your typical mechanical style single phase watthour meter. The voltage and current coils are arranged such that a current 90 degrees out of phase with the voltage will produce no torque and no rotation. That and a clever magnetic brake make speed proportional to instantaneous power, and thus the meter mechanically integrates VI*cos O*dt.

    [If you're interested in how it works, look up the design -- it's basically a two phase induction motor. The coils will be space 90 electrical degrees apart and to produce torque, a rotating field must be produced which requires the currents be 90 degrees out of phase with each other, which is what a two-phase system is. Now, the voltage coil is high inductance between the two hots on a 120/240 3-wire single phase system, and thus current through there is about 90 degrees out of phase with voltage. The current coils are low inductance coils in with the hot feeder conductors. Thus when that load current is in phase with the voltage, they are 90 degrees out of phase with the current in the voltage coil. When you have a pure reactive load, however, load current is 90 degrees out of phase with voltage to begin with, and thus the two coil currents are now *in phase* and no torque is produced.

    Normally, an induction motor would attempt to accelerate to near synchronous speed (less whatever the slip factor is). So enter the magnetic brake. You have a permanent magnet the field of which the rotor wheel must spin through. This produces a back torque proportional to speed, and thus equilibrium speed of the rotor will be proportional to the torque generated by VI*cos O via the coils.

    The voltage coil will of course have some small resistance, and the current will not be exactly 90 degrees out of phase. So there is an adjustment to compenstate for that, as well as other adjustments for the magnetic brake and some other things.

    Note that the voltage coil is between the two hot wires and thus doesn't see neutral voltage drop in the standard design. The power company pays for voltage drop over the hot wires of the feed, but you pay for neutral drop.

    Of course, the old mechanical designs are going the way the dinosaur and are being replaced by electronic versions that do the integrations electronically.

    If you're interested in AC power meter accounting, there is something called Blondel's Theorem, derived way back in the late
    1800s, which states that, in a power system with N supply conductors, one must measure N - 1 voltages and currents, and the voltages must be between the N - 1 conductors with the current coils and the Nth one without it.

    A meter that does that is Blondel compliant and will be accurate in all cases. However there are some tricks and thus some non-Blondel compliant meter arrangements. Technically, the single phase residential meter described above is non-Blondel compliant because it doesn't measure the two hot to neutal voltage, only the hot to hot and thus misses neutral drop.

    Another non-Blondel arrangement was used on some old "high-leg delta" systems (240V delta 3-phase system with the center tap brought out and grounded on one of the supply transformers, giving 120/240V between those. The other leg was thus 208V to ground, and not used. If you tried to use the high-leg to ground for something, the meter would be innaccurate, and I forget who it favored, that is did it measure high or low.

    Anyway, the newer electronic meters are all Blondel compliant, and multi-voltage, meaning one meter can be used on a variety of services. ]

    Now, all that rambling out of the way:

    No residential customers that I know off have ever been penalized for power factor, since it's not much to worry about with residential loads. Industrial, as mentioned above, is a different story.

    So load power depends on power factor, not just current. However, I^2R losses do depend on current, which is why low power factor is a bad thing.


    -Richard

  15. #15
    Join Date
    Feb 2004
    Posts
    1,087
    Quote Originally Posted by baskerbosse View Post
    Back in the 80s when I worked at a factory, we used to have capacitors installed to offset the inductive load of all the motors on the factory floor.
    (-since capacitors phase shift in the opposite direction to coils)
    This is probably done by power electronics these days..
    Nope. It's still done with big honkin' capacitors.

  16. #16
    Join Date
    Jun 2005
    Posts
    13,860
    Also, in general it seems strange to me to say "recycle electricity". It reminds me of an email newsletter I used to receive that claimed it was printed on "100% recycled electrons."
    As above, so below

Similar Threads

  1. Replies: 9
    Last Post: 2011-Apr-04, 02:17 AM
  2. Students Find Rare “Recycled” Pulsar
    By Fraser in forum Universe Today
    Replies: 0
    Last Post: 2011-Feb-02, 09:50 PM
  3. Recycled sf plots
    By ToSeek in forum Small Media at Large
    Replies: 20
    Last Post: 2008-Apr-10, 09:40 PM
  4. The Recycled Universe
    By BOZO in forum Against the Mainstream
    Replies: 2
    Last Post: 2007-Aug-05, 11:35 PM
  5. Recycled Missiles?
    By Eoanthropus Dawsoni in forum Off-Topic Babbling
    Replies: 22
    Last Post: 2005-Aug-03, 08:49 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •