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Thread: DC watts to AC watts conversion equation

  1. #1
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    Default DC watts to AC watts conversion equation

    PV modules are rated in DC watts, utilities net metering is calculated in AC watts. Does anyone recall the engineering conversion from DC to AC watts? Can anyone identify the typical inverter's DC watt input to AC watts output conversion/results?

  2. #2
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    dc watts = ac watts Watts are a measure of power or heat. 5V DC @ 1 A = 5W, same with AC 5VAC @ 1A = 5W

    As for inverter conversion losses, they vary widely from 60% to 95%, somewhat tracking price, higher price = higher efficiency. (not counting ebay inverter scams)
    Reputable mfgs publish an efficiency chart for their inverters

    Hope that helps. Mike
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
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    Default DC watts minus inverter loss = AC watts credited?

    Mike90250, Thanks for your reply.

    If for example, a grid-tied, 1kW DC system, is connected to a 95% efficient inverter, assuming that is the total loss (assuming unity power factor), are you saying the utility will recognize the contribution of 950 W AC?

  4. #4
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    Quote Originally Posted by crlare View Post
    Mike90250, Thanks for your reply.

    If for example, a grid-tied, 1kW DC system, is connected to a 95% efficient inverter, assuming that is the total loss (assuming unity power factor), are you saying the utility will recognize the contribution of 950 W AC?
    Yes, except you might have a fridge running, or other local load in your house, which will use off your PV, and the balance will feed the grid.

    Depending on your meter. Some meters run backwards, some run forward as you feed, and you pay for what you give !! When you get permitted grid tie, they change the meter to the type to match your service. If you have just installed the system and they have not changed the meter, you may get odd results.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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