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Thread: Solar systems and mains failure

  1. #1
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    Solar systems and mains failure

    For safety reasons my solar system requires the mains to be alive before is is connected to the grid. So if I was to have a power failure during the day surely the system would see the output of the solar system across the grid input and still remain connected. Why does it disconnect?
    Jim VK2MAD
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    '17 Isuzu D-Max

  2. #2
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    I believe it disconnects from the grid so nobody gets zapped from the power. Some poor sparky working on lines he thinks are dead cops it from power feed in by your panels

  3. #3
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    also if your house catches on fire, the firefights will isolate the mains, and start praying that the solar is also isolated

  4. #4
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    Thanks guys, I realise that but my question was that as the o/p of the inverter is connected to the supply line and the inverter is fired up with 240 on the supply line why doesn't the inverter sense its own o/p and self run?
    Jim VK2MAD
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    '17 Isuzu D-Max

  5. #5
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    I guess unless your solar can power the whole neighborhood then the output voltage will still drop below nominal. Not sure what would happen if everyone in the neighborhood had solar capacity > demand.

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    Quote Originally Posted by jx2mad View Post
    Thanks guys, I realise that but my question was that as the o/p of the inverter is connected to the supply line and the inverter is fired up with 240 on the supply line why doesn't the inverter sense its own o/p and self run?
    its not designed to work like that. im not understanding what your not understanding. both "the booger" and my answer covers your question.

  7. #7
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    Quote Originally Posted by jx2mad View Post
    Thanks guys, I realise that but my question was that as the o/p of the inverter is connected to the supply line and the inverter is fired up with 240 on the supply line why doesn't the inverter sense its own o/p and self run?
    I think the reason it works like this is because your solar system might generate X kW at 240V at any one time but you might be drawing X+Y kW at 240V. If you loose the grid your not going to meet your power demand from solar alone and the result is effectively a localised 'brown out' which can causes damage to your household appliances.

    To protect the electrical appliances the inverter shuts down. As said by others, it also shuts down to prevent back feeding into the grid which cab cause safety issues for those working on the grid.
    2011 D4 3.0 SDV6
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  8. #8
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    Simple really, the grid inverter reads the voltage of the mains it's trying to pump power into. If it rises above the upper preset voltage (say yer house supply went open circuit) or below the lower set voltage (yer house and half the street are dragging the voltage down to zero) the inverter shuts down. Until the line voltage returns to between those set limits it stays disconnected. The chance of a disconnected supply being maintained by solar alone to between the limits is very remote. Grid inverters aren't voltage regulated like in DC battery systems, they are designed to maximise their output power at all times, or shut down entirely.

  9. #9
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    solar and mains power

    Quote Originally Posted by jx2mad View Post
    For safety reasons my solar system requires the mains to be alive before is is connected to the grid. So if I was to have a power failure during the day surely the system would see the output of the solar system across the grid input and still remain connected. Why does it disconnect?
    its due to two factors the inverter requires ac voltage and dc voltage to work and the anti island in the inverters as per Australian standards to prevent exactly what you asking that a number of inverters on a grid could falsely create their own grid and energize systems that people are working on also the inverter is not able to connect within a 60 sec delay again as per Australian standard to prevent again islanding by inverters after reclosures on the grid switch I after failure ie in storms or brown outs etc MKE Solar electrician

  10. #10
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    Just a question with the purpose of learning something.
    Are there available a kind of hybrid system that in the events of power black out (like in the cyclone affected areas) the solar system can start charging batteries so the house can have the own power via an inverter?

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