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Coherent signal addition

  1. Jul 4, 2012 #1
    I have a solar energy system at my home. It basically uses an inverter that converts DC from the solar panels to AC that is phase-locked to the service from our electric company, then adds the two together to feed the home. There are two meters – one to measure the energy produced from solar, and one to measure the energy we buy from the electric company. A separate system measures our total home consumption.

    Last March, the inverter failed and was replaced. After the replacement, I noticed the total consumption increased by as much as a factor of two, and complained. After a service call they told me that they had wired the new inverter backwards, but that it was now fixed. That made sense to me – hooking up the inverter backward would have meant the solar was subtracting from the paid service. Anyway, the consumption went back to normal, but the additional consumption was recorded by the service meter and I had to pay for it.

    My question is, where did the additional energy go? We didn’t consume it, and nothing got burning hot. Or, in more general terms, when you add two signals out of phase and thus cancel them, where does the energy go? For example, if I were able to align two lasers (same wavelength and perfectly coherent) so that the electric fields cancelled each other, would the light disappear? Would the lasers stop consuming power? Would they burn each other out?
  2. jcsd
  3. Jul 5, 2012 #2


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    If it was wired backwards I'm pretty sure the inverter would just shut down. So your consumption probably doubled because your panels wern't generating any electricty NOT because they were somehow feeding it in out of phase.
  4. Jul 5, 2012 #3
    No, according to its production meter it was producing at about the same rate as always.
  5. Jul 6, 2012 #4


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    Do your solar panels put out enough power to reduce your consumption from the grid by 50%?
  6. Jul 6, 2012 #5


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    Only other thing I can think of is some kind of metering issue. If they connected the solar panels to the wrong side of your consumption meter that might explain it.
  7. Jul 7, 2012 #6
    Drakkith: Yes, on a clear summer day we generate ~ 30 kWh, in the winter ~ 20 kWh. Our consumption varies from 15 to 40 kWh depending mostly on how much we use the air conditioning.

    CWatters: Thanks for the thoughts.
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