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run inverter off panel without battery?

Discussion in 'Photovoltaics' started by Robert Morein, Jun 24, 2004.

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  1. Is it possible to run an inverter off a panel without a battery? The purpose
    would be to greatly extend the permissible length between the panels and the
    battery bank, by using a battery charger at the other end.

    I'm concerned about the possibility of inductive kickback from the inverter,
    when turning of/on, that would normally be absorbed by the capacitance of
    the battery.

    It seems to me that spikes of both polarities must be considered, so it's
    not simply a question of the reverse breakdown voltage of the panel.

    It's not enough to know that while running, an inverter produces no
    kickback. The possibility of accidental disconnection or turnoff is always
    there.

    One could put a car stereo capacitor across the panels, and it might help
    starting the inverter, but I'd like to know if this is of any real concern.
     
  2. Thanks.
    I had forgotten that the 12V nominal panel voltage does not represent the
    actual swing that occurs.
    The inverter may refuse to start, simply because the open circuit voltage of
    the panel is much higher.
     
  3. steve

    steve Guest

    My expectation is that at best the transient load regulation performance
    of the inverter would be degraded without a nice low impedance at the
    inverter D.C. power input.

    At worst the inverter could possibly become unstable, even if it started.

    The other concerns regarding momentary drop of panel voltage or
    excessive panel output voltage making inverter startup impossible also
    seem valid to me.

    This is not a scheme I would attempt if I had expensive equipment
    running at the output of the inverter!

    With CAREFUL investigation regarding the inverter specifications (input
    DC source characteristic requirements, OV / UV limits, etc) it could
    accomplish what you are looking for, but it sounds like a bit of a
    science project to me :)

    Steve
     
    loomsolar likes this.
  4. All of your objections are valid.
    The only thing at the other end would be a two-stage battery charger, such
    as a Samlex, that can simultaneously charge a battery and run an inverter.
     
  5. Steve Spence

    Steve Spence Guest

    1. PV output voltage tracks battery voltage. No "regulator" needed. Charge
    controller needed if panel can exceed battery charge rate. small panels
    usually don't. I don't use a charge controller with my 115ah battery and 15
    watt panel on the camper.

    2. The battery is the buffer between the inverter and the pv panel. You can
    pull more watts from the battery than the pv panel supplies. That's the
    point of the battery.



    --
    Steve Spence
    Renewable energy and sustainable living
    http://www.green-trust.org
    Discuss vegetable oil and biodiesel
    powered diesels at
    http://www.veggievan.org/discuss/
     
  6. Steve Spence

    Steve Spence Guest

  7. Steve Spence

    Steve Spence Guest

    I did not see where he was foregoing a battery. I apologize if I missed it.
    Not a good move if I may say so. Put a battery in there. Even on my son's
    solar cars, we put a small NiCad or cap to level out momentary shading.

    --
    Steve Spence
    Renewable energy and sustainable living
    http://www.green-trust.org
    Discuss vegetable oil and biodiesel
    powered diesels at
    http://www.veggievan.org/discuss/
     
  8. Thank you Steve, John, Steven Spence.

    It appears that the best answer is an MPPT charger, and the best of them is
    the Outback MX-60.
    With this charger, I can run the three panels in series at 36V, reducing
    both transmission losses and power point mismatch.
     
  9. boB

    boB Guest

    You should use at least a small battery connected to the inverter
    battery terminals, for one, to act as a filter (ripple voltage) and
    also to start the controller, since most controllers will not start up
    with PV input alone.

    That might work OK.

    boB
     
  10. I bought a 12V inverter, because of the flexible options with respect to
    hooking up to cars.

    But your point is correct, and I have solved it in the following manner: The
    charge controller will be an Outback MX-60, which auto-senses the panel
    voltage. I can string two or three panels in series, and keep the battery
    bank voltage at nominal 12V.
     
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