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How to draw power from the grid, but not export to the grid???

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  1. silkwood is offline Junior Member
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    How to draw power from the grid, but not export to the grid???

    I am not familiar with current transformers. I believe they can tell me in which direction current flows. I have a problem with 240 vac supply. I want the current to flow in one direction only. Enphase has a gadget called Envoy S Metered, which when connected to their S270 or S230 micro inverters can measure production as well as consumption power. This gadget can be set to Zero Grid Export, but can import power from the grid.
    I would like to build a gadget which would tell me when power flows to the grid and then activate a relay to prohibit power going to the grid. I can not use the Enphase gadget as I have M250 micros and this gadget is not compatible with those.
    Can anyone give me a clue as to how to draw power from the grid, but not export to the grid???
    Cheers
    Silkwood.

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  3. SecondGen's Avatar
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    Quote Originally Posted by silkwood View Post
    I would like to build a gadget which would tell me when power flows to the grid and then activate a relay to prohibit power going to the grid.
    The easiest solution will be to find an inverter with this feature built in. To DYI something like this, the first thing that comes to mind would be a reverse power relay tied to a shunt trip breaker.

    Essentially what would happen is your grid breaker would trip any time the reverse power relay detects power flow to the grid. Excess power could be fed to a battery bank. You would have to manually close the circuit breaker when you wanted to return to grid power, which is undesirable.

    To further complicate things, you would have to be sure that you were generating less than you were using before closing the breaker, otherwise it would trip free. Some kind of monitoring would be in order. You would also probably need a synchronizing relay because the inverter and grid power have to be in phase before tying them together, otherwise things go BOOM!

    Finding all of the individual components for a 240V system would be difficult and expensive. Pre-made microprocessor units have all of this stuff built right in. You might be able to find an add-on device for your existing system but it might be worthwhile finding a whole new inverter with this capability.

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