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Thread: Set up to run a 12000 btu window unit?

  1. #1

    Default Set up to run a 12000 btu window unit?

    Hi, sorry, I'm new to this. I live in Houston and we have alot of sun. I would like a solar power kit that I could piece together to run a 12000 btu window AC unit. I figure a 3000 watt inverter, but what would I need in the way of solar panels and batteries. I really only want to run the ac unit for about 4 hours a day. Thanks.

  2. #2
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    People will tell you that you have to know how many watts your ac unit will use during the course a day. Watts seem to be the baseline in figuring requirements for everything else. They sell a doodad called a killawatt that you plug into your outlet, then plug the ac into the killawatt. It will show you the draw the air conditioner really uses. You can also try looking at the ac or it's manual. Sometimes these figures are listed there. You will be suprised at how many panels and batteries it takes to run power hungry things like an ac unit. I am still new and learning. Usually one of the heavyweights will chime in with a mathematical example, but I do know you need to know the wattage requirement first. Look around, this has been explained a million times, yet the heavyweights here explain it time and time again because they are patient and generous that way.

  3. #3
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    When you price out a 3,000W pure sine inverter, a modest battery pack to run it for 1 hr, and then the solar panels - at $500 for a 200W panel ($2.5 watt), you want to be sitting down. But, first, yes, we need to know the wattage, and the start-up current that it takes. Also, it's worth gettting a energy star version, with a high SEER rating, costs more up front, but less over it's life, of power consumed.

    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

  4. #4
    Solar Fanatic
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    Quote Originally Posted by fedupwithbills View Post
    Hi, sorry, I'm new to this. I live in Houston and we have alot of sun. I would like a solar power kit that I could piece together to run a 12000 btu window AC unit. I figure a 3000 watt inverter, but what would I need in the way of solar panels and batteries. I really only want to run the ac unit for about 4 hours a day. Thanks.
    I can tell you exactly what you need. I need one more small piece of info from you, the SEER rating of the Window Shaker. However I can pretty much guess because they are all around 10, with a power factor of .8.

    So here we go. The unit will draw 12,000 btu/ 10 Seer = 1200 watts of real heat power. With a .8 PF it will require 1200 watts / .8 1500 Kva.

    OK to run it 4 hours per day it will use 1.5 x 1500 Kva x 4 hours = 9 Kva. So since you are in Houston TEX the shortest hot weather month is September with a 5.3 Sun Hour day so your solar panel wattage required = 9000 KVa / 5.3 hours = 1700 watts Estimated cost of panels is $3 per watt = $3 x 1700 = $5100

    To save a few pennies to use the smallest amperage Charge Controller you will have to run the system at 48 volts. That means you will need a 1700 watts / 48 volts = 36 amps. So you will need probable a 60 Amp MPPT Charge Controller. A good efficient one will run you about $550.

    Next is the batteries. You will need 45 Kwh storage capacity so at 48 volts the AH rating = 45,000 wh / 48 volts = 937 AH. Since there is not a 937 battery cell you will have to use something like a Rolls S-1380 a 2 volt 1050 AH battery. You will need 24 of them to make 48 volts and unit cost is $360 so 24 x $360 = $8640

    You will differently need a good quality True Sine Wave inverter. 300 watts for a really good one should be able to start a AC unit and a good one cost around $1.50 per watt = 3000 x $1.50 = $4500.

    So in all just for the piece parts of the system you are looking at around $18,790 plus materials, labor, and shipping cost. Oh did I mention you will need to replace those batteries in about 5 years?

    Not sure exactly what you pay for electric in Houston, but I suspect you are using Reliant Energy and they charge depending on your plan around 10 cents per Kwh. Using solar to run your AC unit will cost you about $2.50 per Kwh or about 25 times more than you pay now, but rather than pay a monthly bill to Reliant, you have to come up with a full 5 years in cash, in advance to use solar power battery systems.
    MSEE, PE

  5. #5

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    Thank you.

  6. #6

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    Thank you sir.

  7. #7
    Solar Fanatic
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    Quote Originally Posted by MYSELF!
    Usually one of the heavyweights will chime in with a mathematical example
    See? Awesome huh? ...outside of the numbers you get back. hehe

    Mike90250 always suggests changing to energystar appliances when people ask questions like this and for the time being, I think that is the best advice that can be given. They can make a big difference. Check them out. Don't give up on reducing your footprint and electric bill!

  8. #8
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    Your best bet, is to install a small grid intertie system (1-3KW) to offset the cost of running any of your household.
    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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