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Thread: Window A/C run on Solar

  1. #1

    Default Window A/C run on Solar

    I am new here,

    I know I am very far from the setup that I need to run a window A/C but figured I would let you know what I have right now.

    I live in a trailer that does not have access to power lines. We currently are running all of our power from a 2300 Watt Gas Generator. My goal is to be able to run solar and keep the generator off.

    A few days ago I bought a basic solar panel kit from harbor freight 45 Watt Solar panels, 125 Amp Hour Deep Cycle Battery, 2000Watt Modified Sine Inverter.

    I havent had much time testing to see all that I can run. But I have tried running some lights, tv, fan, etc. Basic lower power items with no problems. (except the tv makes a buzzing sound even when it is off).

    I also tried turning my window a/c on. It's below 5000 BTU actual amps are 4.8. I was able to run the fan portion with no problems, but when I switched it to COOL it tried starting for about 1 second than turned off, and my Inverter started beeping its low voltage alert.

    My question. This AC is 4.8 AMPS. I would love to be able to run it for at least 6 hours a day, and also be able to run small lights, fan, and possibly a few other basic items.

    With the current setup I have now. How many more solar panel would I need, and batteries.

    I was gambling getting at least (2) 200 watt panels which would bring me to 445 Watts total. But before I go through spending that much money for the panels and batteries I need to know if I will be able to run the AC, if not I dont want to spend extra money.

    Please help, im fairly new to this but really would love to be able to run all solar. How many more watts of solar panels would I need, and how many more batteries that are rated 125 amp hours to be able to run the AC for at least 6+ hours.


    Let me know if you need any more info, and ill try to help.

    Thanks for reading and responding. Well appreciated.
    -Cory

  2. #2
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,247

    Default Re: Window A/C run on Solar

    cory,
    unfortunately that 4.8a is at 125vac and not 12vdc. the wattage will be 4.8a x 125v = 600w. last time i checked 400w was only 2/3rds of that and you'd need some more for losses and efficiencies which could add another possible 300w and all of this is only while the sun shines. you may want to run the generator for the a/c and you could use small 12v fans from the battery that was charged by solar. try leds for lights too.
    speaking of the battery, the incident of the low voltage alarm was caused by the huge draw upon the battery when trying to run the a/c. what you were probably seeing was well over 50a at 12vdc being drawn to produce the power needed at 125vac. i'm not sure what your battery is rated, but it's clearly not enough and you should never run a battery down beyond 50% as this takes away too much useful battery life from the battery.
    NIEL

  3. #3

    Default Re: Window A/C run on Solar

    Quote Originally Posted by niel View Post
    cory,
    unfortunately that 4.8a is at 125vac and not 12vdc. the wattage will be 4.8a x 125v = 600w. last time i checked 400w was only 2/3rds of that and you'd need some more for losses and efficiencies which could add another possible 300w and all of this is only while the sun shines. you may want to run the generator for the a/c and you could use small 12v fans from the battery that was charged by solar. try leds for lights too.
    speaking of the battery, the incident of the low voltage alarm was caused by the huge draw upon the battery when trying to run the a/c. what you were probably seeing was well over 50a at 12vdc being drawn to produce the power needed at 125vac. i'm not sure what your battery is rated, but it's clearly not enough and you should never run a battery down beyond 50% as this takes away too much useful battery life from the battery.
    So if I am understanding this correctly. You are telling me if I want to run my A/C (during daytime hours only) directly from the solar panels (without batteries) I will be able to do this with at least 700watts of panels, connecting inverter directly to panel.

    Also If I was to add several more batteries to the one 125 amp hour battery I currently have, would I still need the 700 watts of panels or could I slightly get away with less.

    I want to totally avoid the cost of gas for the generator by not having to run it at all. Also, I plan on mostly using the AC and other power mostly at nighttime hours when the sun has gone down, that is why I think I will need the batteries.

    Thanks again.

  4. #4
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,247

    Default Re: Window A/C run on Solar

    (my comments in bold for within your post)

    Quote Originally Posted by cswaite View Post
    So if I am understanding this correctly. You are telling me if I want to run my A/C (during daytime hours only) directly from the solar panels (without batteries) I will be able to do this with at least 700watts of panels, connecting inverter directly to panel.

    no, you will need the batteries and you may need upwards of 800-900w of pv. this allows for no extra to the batteries for night use at all.

    Also If I was to add several more batteries to the one 125 amp hour battery I currently have, would I still need the 700 watts of panels or could I slightly get away with less.

    each 125ah battery will yield 125ah x 12v = 1500w of power of which up to 1/2 of that is usable or 750w per battery. unfortunately drawing at half of a battery's full rating will kill it in short order so several batteries are needed for every hour you plan on running the a/c and that's still stressful on them.

    I want to totally avoid the cost of gas for the generator by not having to run it at all. Also, I plan on mostly using the AC and other power mostly at nighttime hours when the sun has gone down, that is why I think I will need the batteries.

    this is a large undertaking and will not be done simply with a few batteries and a few pvs and the longer you run large loads a/c presents the more you'll need to supply and store this power. i did base this on the a/c units running full bore constantly as i figured their short runtime will be maxed out with a great deal of heat to get rid of.

    Thanks again.
    with a/c for your trailer, i don't foresee you eliminating the generator without many pvs and batteries that you most likely don't have the room for and the expense is another area.
    2 more pieces of bad news here and that is the modsine inverter will shorten the lifespan of the a/c and any other item with a fan or electric motor. if you can live with that you will also need roughly another 20-25% power generated from pvs to make up for the wasted power eminating from the harmonics of the modsine inverter.
    NIEL

  5. #5
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,821

    Default Re: Window A/C run on Solar

    Cory,

    As Niel said--you are nowhere near capable of running your A/C with your existing solar system...

    The best thing for you to do would be to address the issues in multiple steps before you buy your next piece of equipment.

    1. Conservation: Heavy insulation (especially roof), double pane windows/drapes/styrofoam blocks, out door shading of windows/walls/roof, sealing air gaps, reducing interior heat (computers, cooking, etc.). If you need lots of fresh air--look at installing a heat recovery ventilator to reduce heat/cool loss. Taking a guess you are around Dallas Tx and cannot use a "swamp cooler". Conservation (even "extreme conservation) is always your best spent money... Much better value than just throwing Solar RE / Panels at the problem.

    2. Picking the best A/C system for the job... Your window A/C system probably has a SEER of ~10. If you get a mini-split system you can get a SEER of ~20--either 2x the cooling or 1/2 the energy usage. Read the Sanyo Mini-Split thread (if you have not already).

    3. Now that you have conserved and installed (or plan to install) very efficient appliances... You need to know how much power they will consume. The Kill-A-Watt meter (120 VAC 15 amp) will measure your loads for you so you can size the rest of your off grid system. Note, a genset is noisy/fuel expensive way to make power--but it is still cheaper (up front) that a full-blown solar RE off-grid system.

    4. Sizing... Obviously, I don't have any numbers for your installation--but lets make some guesses--and you can adjust based on your needs. So, this is how I would suggest to proceed:

    Assume:

    April-October cooling season and plan for zero generator use (except during bad weather)
    Run A/C 10 hours per day (and you will need a battery bank)
    Window unit draws 600 watts
    Sanyo Mini-split draws 300 watts (2x as efficient)
    Assume 500 watt*hours to run lights, small fan, radio, little bit of computer (average watts * hours turned on = Watt*Hours)
    Near Austin Tx
    Assume Off-Grid system with 0.52 efficiency (solar panels to battery to AC inverter to 120 VAC power)

    Window A/C = 600 watts * 10 hours + 500 Watt*Hours = 6,500 Watt*Hours per day (summer) load
    Mini-Split = 300 watts * 10 hours + 500 Watt*Hours = 3,500 WH per day (summer) load

    Use the PV Watts Website to predict how much power a 1kW array near Austin Tx will produce (derating = 0.52 for off grid, rest defaults):

    Code:
    Results for 1kW of panels in Austin Tx
    
    Month
    Solar Radiation (kWh/m2/day)
    AC Energy (kWh per month)
    Energy Value ($ at 9.7 ˘/kWh)
    
    1      4.32          65        6.30   
    2      4.96          67        6.50   
    3      5.47          81        7.86   
    4      5.52          77        7.47   
    5      5.54          78        7.57   
    6      5.93          79        7.66   
    7      6.21          85        8.25   
    8      6.22          85        8.25   
    9      5.77          78        7.57   
    10     5.65          80        7.76   
    11     4.60          65        6.30   
    12     3.96          59        5.72 
    =======================================  
    Year      5.35          900    $87.30   
    So, 77 kWhrs per month in April is the minimum kWhrs per month. Or

    77 kWhr per month / 30 days per month = 2.57 kWhrs per day per 1,000 watts of solar panels

    For the Window A/C unit:

    6.5 kWhs per day / 2.57 kWhr per day per 1,000 watts of panels = 2,530 watts of solar panels

    For Mini Split system:

    3.5 kWhs per day / 2.57 kWhr per day per 1,000 watts of panels = 1,362 watts of solar panels

    To size the battery bank... Assume 12 volt bank, 80% efficient flooded cell batteries, and 85% efficient AC inverter. Recommend 3 days without sun, and 50% maximum discharge of battery bank (for longer battery life):

    Window A/C unit:

    6,500 WH * 1/0.80 * 1/0.85 * 1/12 volts * 3 days * 1/0.50 = 4,800 AH of 12 volt batteries

    Mini-Split AC unit:

    3,500 WH * 1/0.80 * 1/0.85 * 1/12 volts * 3 days * 1/0.50 = 2,600 AH of 12 volt batteries

    I will stop at the moment... Probably enough information to keep you busy for a bit. There is a lot more (equipment sizing/recommendations, etc.)--but it will just confuse you more right now.

    The above is fairly conservative based on SWAGS (scientific wild ass guesses). But it will give you an idea of what you are up against.

    Questions?

    -Bill

  6. #6
    Join Date
    Sep 2006
    Location
    Willits, CA
    Posts
    5,626

    Default Re: Window A/C run on Solar

    Quote Originally Posted by BB. View Post


    Window A/C unit:

    6,500 WH * 1/0.80 * 1/0.85 * 1/12 volts * 3 days * 1/0.50 = 4,800 AH of 12 volt batteries

    Mini-Split AC unit:

    3,500 WH * 1/0.80 * 1/0.85 * 1/12 volts * 3 days * 1/0.50 = 2,600 AH of 12 volt batteries
    Wow - that's a bunch of batteries in parallel. If one was to cut the 3 days to only 2 days, that's still a bunch of batteries, even for the split system.

    1731AH @ 12V = 20772WH stored. Even going to a 48V system (batteries in series, not parallel, that's 433 AH . So going even to the Crown 6v 395A battery
    http://store.solar-electric.com/cr395amdecyb.html
    would be just a tad short, but I think it's the way to go,
    Crown 395 AH 6-Volt , L-16HC size. 11.625" x 7.0" x 16.125", 121 pounds.
    You would need 8 of those beasts, and a truss for what's left of your groin. Just about a half ton of batteries. Ouch

    Well, at least you can build all the PV panels into a carport to shade and park under.
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  7. #7

    Default Re: Window A/C run on Solar

    I can't stop myself from commenting on 'solar kits'. Sorry!

    Can we get these things banned?

    It appears that friend Cory is the latest in a long and never-ending line of victims to predatory salesmanship. There are too many companies offering these "kits" or "packages", all of which are promoted with false claims of their ability to provide usable power from the sun. Some are just exaggeration, others constitute outright fraud.

    The basic pre-packaged solar outfit consists of:

    1). Severe underestimating of the user's power requirements.
    2). Panels that are insufficient to power anything larger than a pocket calculator.
    3). Over-rated, undersized batteries best used for starting a lawnmower.
    4). An inverter which can only achieve its claimed output wattage under carefully controlled laboratory conditions. And only then with a bit of luck.

    These things are a prime example of Tony's (Icarus) famous "Ready, Fire, Aim" maxim and are to be avoided like a fatal disease.

    I think Cory's best bet is; conservation, run everything possible but the AC off solar, use the gen when necessary for the big loads.

    And again, sorry for the rant.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  8. #8
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
    Posts
    5,025

    Default Re: Window A/C run on Solar

    I just ordered some logging tools from Northern Equip. Fairly good, hard to find stuff,, at a reasonable price. Included in the order was a new catalogue. (I am doing this from memory,, so the numbers may be off a bit,, but you get the idea!)

    In that catalogue was a "1250 watt solar kit,, provides 1250 running watts of solar power" Price,,,~$4000!

    Looking into the system just to satisfy my curiosity, here is what was included. 2 ~125 watt 12vdc panels (sunforce brand,, don't know about UL) 2 T-105 type batteries of some no name brand. 1250 watt inverter,(no mention of brand or if it was MSW or pure) A couple of wiring boxes etc.

    I did a quick calc,, and even if I paid full retail for all the stuff, here is how much I would spend to piece this "kit" together.

    250 watts of Pv @ $5 (I know I can get them for $3) $1250
    2 T-105 batteries 300
    Inverter 1000
    Misc wiring stuff 500
    Total 3050


    This is using very generous pricing. In addition,, there is no mention as to what the "1250 running watts" means. To a newbie,, one would think that you could run 1250 watts while the sun is out, rather than ~125 you might be able to pull on a perfect day!

    Not only should these things be banned,, someone should go to some AG and get these guys for deceptive advertising, fraud etc.

    I have no problem with a vender selling what ever,, but to allude that these things will do what they won't verges on the criminal.

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  9. #9

    Default Re: Window A/C run on Solar

    I guess if we want to run the AC we will use the generator. This sounds way out of my budget, I dont have several thousand dollars to be spending just to be able to run the AC. It would be a lot cheaper to run the generator when it is really hot. I figure it should only be hot for 2-3 more months (southern California).

    After those 2-3 months we can use the solar strictly to run things like tv's, lights, etc. And have the generator for times when we need to use the microwave or vacuum or anything that pulls a lot of power. In the winter time we can probably get away with sweaters, jackets, and blankets for the most part. It only gets in 30's here at the lowest in winters.


    Thanks so much for spending the time calculating and helping me, really appreciate it.

  10. #10

    Default Re: Window A/C run on Solar

    Quote Originally Posted by icarus View Post
    I just ordered some logging tools from Northern Equip. Fairly good, hard to find stuff,, at a reasonable price. Included in the order was a new catalogue. (I am doing this from memory,, so the numbers may be off a bit,, but you get the idea!)

    In that catalogue was a "1250 watt solar kit,, provides 1250 running watts of solar power" Price,,,~$4000!

    Looking into the system just to satisfy my curiosity, here is what was included. 2 ~125 watt 12vdc panels (sunforce brand,, don't know about UL) 2 T-105 type batteries of some no name brand. 1250 watt inverter,(no mention of brand or if it was MSW or pure) A couple of wiring boxes etc.

    I did a quick calc,, and even if I paid full retail for all the stuff, here is how much I would spend to piece this "kit" together.

    250 watts of Pv @ $5 (I know I can get them for $3) $1250
    2 T-105 batteries 300
    Inverter 1000
    Misc wiring stuff 500
    Total 3050


    This is using very generous pricing. In addition,, there is no mention as to what the "1250 running watts" means. To a newbie,, one would think that you could run 1250 watts while the sun is out, rather than ~125 you might be able to pull on a perfect day!

    Not only should these things be banned,, someone should go to some AG and get these guys for deceptive advertising, fraud etc.

    I have no problem with a vender selling what ever,, but to allude that these things will do what they won't verges on the criminal.

    Tony
    I think you guys are talking about other solar kits. The one I purchased was from Harbor Freight, and clearly stated 45W Solar Kit. Came with (3) 15 watt panels, panel mount, dc charge controller that has cigarette lighter, usb, and a few other dc jacks directly on the controller, also came with (2) 5 watt lights that plug into jacks on the controller. The regular price is $250. It was on sale for $200, and I was able to use a 20% coupon on top of the sale price, out the door before taxes was $159, not terribly bad to get started in solar.

    Also bought a 2000W/4000W Modified Sine Inverter from them for $159

    Bought a 125AH deep cycle from Walmart, for about $80

    Only spent about $500 total for all of this. (not exact total).

    Even to be able to run lights, tv, fan off this setup will pay for itself. A lot cheaper than having to run the generator which uses a lot of gas just to run these low powered items.

    I do agree with you, there are other kits that are out there that will rob you dry, these criminals should not be allowed to sell such products.

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