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Thread: PV - The magic of it all

  1. #11
    Join Date
    Nov 2015
    Location
    CA, USA
    Posts
    629
    Quote Originally Posted by Carultch View Post
    Electrons don't actually make it from source to load, due to it being AC. It is the "pressure wave" of inter-electron repulsion that flows among electrons in the conductor, that carries the energy.
    This one gets a lot of people. "If the electrons just move back and forth how does that power anything?" I describe it this way, say you have a water pump with a handle on it that moves back and forth to pump the water. If you connect a long stick to that handle and then go to the end of the stick and move it back and forth you are pumping water. The stick I am touching never leaves my hand yet the lever on the pump moves.
    Now think of the stick as a string of electrons in a wire and you move the electrons back and forth inside the wire to move a lever at the end that pumps water. The electrons on your end just move back and forth but the pump handle moves and pumps water.

  2. #12
    Join Date
    May 2011
    Posts
    4,577
    Yeah, just plain electromagnetism is magic. Nevermind solar.

  3. #13
    Join Date
    Sep 2012
    Location
    Clinton, WA
    Posts
    87
    The OP's original question is an excellent one. How the heck does the electricity know which way to flow???

    The water analogy is a great way to think about how it all works. Consider the following:

    You have a large body of water, say a lake. (think zero volts, or ground)
    You have a swimming pool next to the lake.
    It is one of many similar pools, and all the pools are connected by pipes so their water levels are all the same. (think grid voltage)
    The water level in the pools is maintained by a large pump. (think utility power plant)
    The pump sucks water from the lake, and it enters each pool at the elevation of the water level in the pool.
    There are several pipes just under the water level of each pool that draw water off to water wheels. (think loads)
    The water that passes over the water wheels is returned to the lake via a pipe that lies on the ground. (think neutral wire)
    The pump is run at a speed that fills the pools at the same rate as the water drawn off the pools by the water wheels.
    In this way, the water level in the pools always remains the same.
    Another small pump is installed that pumps water into one of the pools at a height just above the water level. This is an inverter.
    If the water wheels are drawing less water from that pool than is supplied by the small pump, the water level in the pool will rise.
    Which will result in water flowing backward through the pipe that normally fills the pool.
    The water that flows backward will fill the adjacent pools.

    How does the water know which way to flow? Simple. It doesn't know squat. It just runs downhill. Electricity works the same way.

    Hope that helps.

  4. #14
    Join Date
    May 2010
    Location
    Wailuku, Hawaii
    Posts
    10

    Backfeed

    We use ct’s Connected to a modbus meter. Ct’s Connected either line or load side of main breaker. The modbus meter connects via rs485 connection to the pv inverter. We can then program the modbus meter to export a max kw, kWh, infinit export, or non export, or a combination of either. The modbus meter tells the pv inverter to produce energy, curtail energy, or shut down.

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