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Way to fool power wall to export to grid

Discussion in 'Tesla Energy' started by Icepicknz, Jul 28, 2018.

  1. Icepicknz

    Icepicknz Member

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    Auckland new zealand
    #1 Icepicknz, Jul 28, 2018
    Last edited: Jul 28, 2018
    Hey guys,

    Anyone know if there is a way to fool the PW into exporting more energy than the house requires so it exports to the grid?
    For instance, could one connect an additional CT to the mix and somehow fake an additional 2kw of load to the house so the PW exports 2kw to the grid?

    I know Tesla keeps marketing about 'virtual power plants' etc and this is pretty much what I want to do. When the grid is at peak time and requires more generation, I'd like to somehow initiate export to the grid. I've calculated that if I do this 700 times (send 13kw over a 3hr period to the grid when price is $1 or more per kw) I could pay off my power wall ($10k) pretty quickly and buy more.
     
  2. wwhitney

    wwhitney Member

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    Location:
    Berkeley, CA
    Certainly this can be done.

    Here in California, a homeowner's agreement with the power company prevents the homeowner from exporting power, unless they have solar panels, in which case the annual export is limited to an estimate of what the solar system is capable of generating. So the only allowed use for this would be for homeowners with solar to time shift their solar generation. I.e. charge their Powerwalls from solar non-peak periods, and discharge that stored solar during peak periods, in addition to the solar power being instantaneously generated. That would be useful, and is not something Tesla currently supports.

    As to how to do it, there a few options. With adequate knowledge of electrical safety, you could run a second conductor through the CTs that measure consumption. E.g if you had a 120V, 100W, useful load, whose schedule you can control and aren't particular about, you could power it with a 14 AWG conductor that is run through each CT 5 times (in the proper direction). Then when the load is on, the gateway will see an extra 1kW of load that isn't there.

    More elegantly, you could add CTs. The Nerio CTs are marked 264A:88mA, meaning they are have a ratio of 3000:1, and Neurio support told me they have no built-in burden resistor and instead use a protective diode. I'm not too knowledgeable about CTs, but I believe that means you could parallel another CT on each Neurio input, and if you used a much lower ratio, you could get the gateway to see a lot more power without wasting energy. E.g., if there is such a thing as a 100mA : 100 mA CT (ratio of 1), then a 43.2K ohm resistor at 120V will dissipate 1/3 W, which the Neurio would interpret as an additional load of 1 kW.

    There are probably some subtleties of this arrangement that I don't understand, so I'm not at point yet where I'd feel comfortable adding CTs. So far the available supported behavior of the Powerwalls hasn't quite been annoying enough to motivate me to figure out all the details.

    Cheers, Wayne
     
    • Informative x 1
  3. BJReplay

    BJReplay Member

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    One thought is two additional CTs, connected via a DPDT relay controlled by say an Arduino. CT1 measures nothing, CT2 is connected to your load. When you want to discharge, switch the relay, and it will appear as if your load has doubled, and the PW2 will discharge into that load, exporting. That just exports your load, rather than a steady 2kW. To get a steady 2kW, you'd need to measure the output of a CT when you have a 2kW load, and simulate that input into a spare CT input on the neurio configured as load.
     
  4. Icepicknz

    Icepicknz Member

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    These are the ideas I Was after. Adding additional CT's is no trouble i have a spare.
    I'm thinking a Y on the CT would have to be the way else the main CT would see export at the time and try dial back the battery so work against each other if they weren't in a Y configuration but clamped and plugged in as a seperate CT on the Neurio.

    @BJReplay i'd love to know more as I want to automate this, not go plug a clamp over a load manually when i want to export to the grid.
     
  5. Icepicknz

    Icepicknz Member

    Joined:
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    Location:
    Auckland new zealand
    @BJReplay in your example, what is the relay doing, obviously not sending a signal just closing the circuit? how does a CT work? if i was to just bridge the two wires would that make it think there is load? then if i added resistance it would limit or tell the neurio how much the load is?
     

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