Solar - Grid Tie - Energy meter increases?

  1. Hi,

    So I trialed a 400W grid tie inverter which I had laying about to experiment with lowering the amount of energy the house is drawing from the grid with a single 100W solar panel I have on the roof to charge some batteries.

    I have a "smart meter" which measures how much power the house is using. Its not the latest ones which send the results back to the supplier. It has a reader which clips round the 4th cable exiting the meter to the fuse box (I'm on a dual tarrif) which connects to a transmitter so that the receiver can be anywhere within 30 metres of it in the house.

    My question is, during a sunny day, I generate about 70 watts. The house uses 600watts all the time (I have a bitcoin miner which utilises 400 watts, and the fridge and freezer together total to 200. 400 + 200 = 600.) When I switch on my inverter, the meter rises to 670W. I thought it should drop 70W instead of increase? Unless the meter is adding the receiving power as well as consumption?

    Any ideas?

    Thanks,
    Owen.
     
  2. jcsd
  3. Some 'Smart' meters register all power as consumed even if it's actually moving from the residence to the grid. It's designed as a theft prevention measure but they are not Solar Guerrilla friendly.
     
  4. Ah ok then. In that case, i have a meter which looks like this - although my meter doesn't have (Multirate) written on it. The meter has a red L.E.D that flashes every now and again. It increases rapidly if a heavy load is turned on such as a kettle. If I was to generate more electricity than what the house is using, would the L.E.D turn green when it flashes, or would it not flash at all?

    Thanks,
    Owen.
     
  5. I don't know but it's a easy experiment to do.
     
  6. jim hardy

    jim hardy 4,342
    Science Advisor
    Gold Member
    2014 Award

    Old analog meters had a disk that turned gears to drive a mechanical KWH counter. That disk had a black spot on it so you could time the turns and figure out what was your rate of consumption.
    One turn of the disk was the number of watt-hours indicated by the Kh written on meter face, 7.2 on this one.
    http://epb.apogee.net/foe/frcmr.asp
    [​IMG]
    That'd be 500 turns per KWH.




    I'd wager that your green LED serves same function as the black spot. Perhaps you could take a stopwatch and find out. Your photo is a little blurry, appears to say something like "1000 mp/kwh" whatever that means.
    Now - if you made more power than you used with an old mechanical meter the disk would turn backward . I don't know what the programmers told your electronic meter's computer to do in that situation.

    Hmmm that's interesting.
    If your 400 watt inverter is 80% efficient its internal consumption is about eighty watts.
    Would it draw that from grid if the solar panel/battery isn't performing? Is there an ammeter on incoming DC ?


    old jim
     
    Last edited: Sep 3, 2014
  7. Unfortunately no.

    By that statement, I meant if the inverter was generating 30watts of power, then the live energy usage on the meter would increase by 30. If it was generating 70watts, then it'll add 70watts to the number etc... E.g If the house is drawing 600Watts, and I turn on my inverter which pushes 70watts into the house, then instead of the "smart meter" deducting 70watts from the total usage, it adds it on as if the inverter is a load, when it isnt. I have the inverters plug (which goes into the mains socket via a plug) connected to an energy meter first so i can see the wattage, volts, frequency, and amps are being generated from the solar panel. This reads 0 when there is no power being generated from the panel. The Inverter is being powered from the solar panel hence why I can get an accurate reading from the plug.

    I presumed the "reader" which clips round the fourth cable coming from the meter actually just detects how many amps are going down that cable. This would probably mean that It's not connected to the right cable - such as the cable coming into the house, therefore It'll probably drop when my inverter generates power instead.

    I'm going to go with the fact that it's not the right cable. What are your thoughts? I know it's a mouthful of a piece (haha) however these are the kind of thoughts running through my head at the moment.
     
    Last edited: Sep 3, 2014
  8. jim hardy

    jim hardy 4,342
    Science Advisor
    Gold Member
    2014 Award

    Having no idea what is either the "reader" or the "fourth wire" i only guessed .

    Can you unclip the 'reader" and put it on upside down? If it's reading current that'll reverse the direction
    if instead it's reading some telemetry , well it's a "bleeping computer" so who knows.

    Modern gizmos - learning about them interesting but painful .

    Electric company can't fail to make a profit that way, can they? There's strange laws about feeding back into grid.
    Electric companies in US must allow you to sell back power but they can put requirements on the interconnect. Most of those are for good reason - home generators not properly connected will backfeed into the grid and they have electrocuted many an unsuspecting lineman who'd properly removed the power feed from his side.
     
    Last edited: Sep 3, 2014
  9. berkeman

    Staff: Mentor

    Again Jim beats me to the call. You *cannot* just connect your power source to the grid without an approved and inspected connection circuit. You can kill somebody if you do a rogue home-brew interconnect. Please PM me about your interconnect module and your inspection/certification papers.

    Lordy, this is dangerous.
     
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