Window A/C run on Solar

cswaitecswaite Posts: 46Solar Expert
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

Comments

  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    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.
  • cswaitecswaite Posts: 46Solar Expert
    Re: Window A/C run on Solar
    niel wrote: »
    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.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    (my comments in bold for within your post)
    cswaite wrote: »
    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.
  • BB.BB. Posts: 25,623Super Moderators admin
    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):
    [FONT=Fixedsys]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   [/FONT]
    

    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 6,665Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar
    BB. wrote: »


    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.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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.
  • icarusicarus Posts: 5,084Solar Expert ✭✭✭✭
    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
  • cswaitecswaite Posts: 46Solar Expert
    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.
  • cswaitecswaite Posts: 46Solar Expert
    Re: Window A/C run on Solar
    icarus wrote: »
    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.
  • BB.BB. Posts: 25,623Super Moderators admin
    Re: Window A/C run on Solar

    Cory,

    Since you are going to be running the genset... Get a Kill-A-Watt meter to measure how much power you use and also keep track of how much gasoline you are burning...

    A well match genset to A/C can run around 5-6kWhrs per gallon of fuel. A poorly matched setup might only give you 1-3 kWhrs per gallon of fuel and cost you 2-6x as much to run.

    Installing an efficient split A/C unit can save another 50% on electrical load and allow you to use a smaller genset too (more fuel efficient at lower loads).

    For example (the following is a rough guestimate--use your numbers if you can), if you are using a "cheap" 2.5 kW genset--they usually run around 5kWhrs per gallon of fuel at 50% rated load (call it 1,200 watts). Below 50% load, your genset will still consume roughly:

    1.2 kW / 5kWH per gallon = 0.24 gallons per hour (at 1,200 watts or less)

    0.24 gallons per hour * $3 per gallon = $0.72 per hour to run the 600w A/C

    Use a smaller/more efficient genset (like the Honda eu2000i) which runs ~15 hours on 1.1 gallons of fuel at 1/4 load (1,600w*1/4=400watts):

    0.400 kW * 15 hours / 1.1 gallons of fuel = 5.45 kWhrs per gallon for eu2000i

    0.6 kWatts / 5.45 kWhrs per gallon = 0.11 gallons per hour

    0.11 gph * $3 per gallon = $0.33 per hour to run on smaller Honda

    Say you run 10 hours per day and a new Honda eu2000i which costs $900 new.

    $900 / (10 hours per day * ($0.72 per hr - $0.33 per hr) = 230 days to break even with new genset

    Anyway--depending on your actual usage and costs--you can run your own costs comparisons about replacing your current genset (or even A/C) and see what your break even cost point would be. You can also factor in other issues (costs to transport and store fuel, life of gensets, other loads like water pumping, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Posts: 5,084Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    Cory,

    I was just illustrating the point,,, there is a lot of overprice stuff,, stuff of questionable value out there,

    T
  • cswaitecswaite Posts: 46Solar Expert
    Re: Window A/C run on Solar
    BB. wrote: »
    Cory,

    Since you are going to be running the genset... Get a Kill-A-Watt meter to measure how much power you use and also keep track of how much gasoline you are burning...

    A well match genset to A/C can run around 5-6kWhrs per gallon of fuel. A poorly matched setup might only give you 1-3 kWhrs per gallon of fuel and cost you 2-6x as much to run.

    Installing an efficient split A/C unit can save another 50% on electrical load and allow you to use a smaller genset too (more fuel efficient at lower loads).

    For example (the following is a rough guestimate--use your numbers if you can), if you are using a "cheap" 2.5 kW genset--they usually run around 5kWhrs per gallon of fuel at 50% rated load (call it 1,200 watts). Below 50% load, your genset will still consume roughly:

    1.2 kW / 5kWH per gallon = 0.24 gallons per hour (at 1,200 watts or less)

    0.24 gallons per hour * $3 per gallon = $0.72 per hour to run the 600w A/C

    Use a smaller/more efficient genset (like the Honda eu2000i) which runs ~15 hours on 1.1 gallons of fuel at 1/4 load (1,600w*1/4=400watts):

    0.400 kW * 15 hours / 1.1 gallons of fuel = 5.45 kWhrs per gallon for eu2000i

    0.6 kWatts / 5.45 kWhrs per gallon = 0.11 gallons per hour

    0.11 gph * $3 per gallon = $0.33 per hour to run on smaller Honda

    Say you run 10 hours per day and a new Honda eu2000i which costs $900 new.

    $900 / (10 hours per day * ($0.72 per hr - $0.33 per hr) = 230 days to break even with new genset

    Anyway--depending on your actual usage and costs--you can run your own costs comparisons about replacing your current genset (or even A/C) and see what your break even cost point would be. You can also factor in other issues (costs to transport and store fuel, life of gensets, other loads like water pumping, etc.).

    -Bill

    You guys have been more than helpful in taking the time to calculate and help me out. Awesome! Thank You!

    Right now we are running a 2,300 WATT generator to run the entire trailer which includes. Window Swamp Cooler, Window AC (4.8 AMP), 2x 32" LCD TV's, a really small microwave, a few CFL's, fans, and that's about it.

    Generally what will be running at the same time is everything but the microwave, in which will be turned on for a few minutes here and there.

    A better option may be for us to buy a cheap generator to strictly run the Window AC.

    and run the bigger generator only if we need to use microwave or run the swamp cooler for a few minutes, etc.

    than run tv's, lights, etc off the solar batteries at night.

    Any thoughts?

    How big of a generator would I need to most efficiently use gas to run the window ac (4.8 amp)?

    Thank you so much for taking the time to help.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    just get the big inverter generator and know all loads up to that point will be dealt with efficiently.
  • BB.BB. Posts: 25,623Super Moderators admin
    Re: Window A/C run on Solar

    Actually, a 2,300 watt genset is probably getting about the smallest/most efficient you can get to run your home. You need capacity to start your A/C while running other loads too...

    A smaller window A/C unit is probably about the maximum a Honda eu2000i can start/run (may have to turn ECO Throttle off to start AC the first time).

    The advantage with the Honda eu2000i is that it has a very wide band where it runs fuel efficient... The Honda will run from ~25-100% loads with fuel flow being proportional to load because it has the inverter/ECO Throttle option (this allows the generator to slow down RPM to conserve fuel yet keep its output at 120 VAC and 60 Hz).

    Most others gasoline generator have a "linear fuel flow" range of ~50%-100%...

    So, a larger genset has a higher minimum fuel flow (which is typically 50% of full power, even if power used is ZERO Watts).

    Diesel gensets are nice and fuel efficient--but usually much larger and they tend to coke/carbon up if running under 50% load (others can expand on what diesels are out there).

    In the end, conservation (insulation, minimizing heat generating devices in the home) should be your first job.

    The Sanyo mini-split system is really nice for small gensets and solar RE systems--because it does not take a large power surge to get the compressor running--and the variable speed (internal inverter) drives the compressor only at the RPM needed to the cooling load at that moment.

    The reason I suggest some sort of Watt*Hour meter for your generator output/loads and logging fuel consumption is that knowing where you are at (fuel costs, energy usage) gives you a firm point to make your next decisions (insulation, energy efficient appliances, alternative sources of power) and to do a dollar to dollar comparison between doing nothing or biting the bullet and spending money now to save in the future.

    If you get any fuel usage numbers (kWhrs used, gallons used, brand/model/size of genset, etc.)--It would be very interesting to see what your situation is... And how close (or far off) my guesstimates are.

    The pain is that the smaller/less power you use--the less efficient generators become. Of course, solar power becomes more of an interesting option the less power you need to generate--but it is still not cheap...

    So you have to think everything out to ensure you really are saving money instead of just spending out of pocket without any gains.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cswaitecswaite Posts: 46Solar Expert
    Re: Window A/C run on Solar

    Thanks guys for the quick and thourough replies. Will give me something to think about.
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: Window A/C run on Solar

    Hi Cory, welcome to the forum.

    Okay, I've got a couple things to say...

    First of all, check out the web site of one of our forum members, 2manytoyz - he started out his solar system using exactly the same kit from Harbor Fright (O_o). You'll get some idea of what it can do by looking at his (excellent) web site:

    http://www.2manytoyz.com/

    Basically, it's a decent *little* solar kit, except the charge controller is horrible junk.



    Now, as to your window a/c...I've been playing with the numbers on this, because I'm planning to add solar and a/c to a camper van I bought a few months ago.

    Basically, I can squeeze a 180w or 200w solar panel onto the roof of my camper, and possibly also 2 or 3 of those 15w panels from HF. I might get two 130w panels on the roof if I covered or relocated the 14" roof vent.

    Either way, I *can't* use a motorhome style roof a/c because then I would have to use even smaller PV panels - and the smallest motorhome roof unit I can find is 11,000 BTU, which would use a lot more power.

    So, a window a/c. I have a big flat spot on the back of the fiberglass roof where I could cut a hole and put in a window a/c. I've looked at a few, and I'm liking the look of the Frigidaire 5,200 BTU unit - programmable and has remote control. It has an EER of 11, and actually uses a bit less power than the smaller 5,000 BTU from Frigidaire which only has an EER of 9.

    http://www.walmart.com/catalog/product.do?product_id=10999788

    [The Frigidaire units also have what they call "LVC" (low voltage compensation). I like the sound of that for something that is going to run on an off-grid system. I suspect that LVC means the unit has a heavier starting capacitor for the compressor - though that's just a guess. Adding a bigger capacitor is a common field modification for motorhome a/c units so they don't draw such a big spike off the generator when the compressor starts.]

    The specs say that the 5,200 BTU unit uses 4.9 amps when cooling (translation: when the compressor is running).

    Okay, now to keep the engineers in here happy, I have to say that I'm going to vastly simplify the math for clarity's sake. The *real* math is more complex, but this is how I do it "on the back of a napkin".

    1 amp at 120 volts is the same as 10 amps at 12volts (simple inversion, no?).

    So, the a/c draws 4.9a@120v - let's round that up and call it 5a since it makes the math easy, and then convert it; 5a@120v = 50a@12v.

    If it runs for an hour on batteries, then it will suck up 50a per hour, or 50 amp*hours (50ah in shorthand).

    Now, I can squeeze at most 4 batteries into the truck (two under the couch, and two way in the back). These will be in the cabin so they have to be AGM to prevent fumes.

    I've decided I'm going with 4 Deka SeaMate 8A31DTM batteries:

    http://www.e-marine-inc.com/products/batteries/dekaagm.html

    These are 105ah@12v, so wired in parallel (to keep everything at 12v) they'll provide 420ah of storage.

    (Which sounds great until you consider that the deeper you drain a battery, the less number of discharge/recharge cycles it will have. Basically, to keep a battery living a long time, you want to drain it no more than 50%, and if you want it to live a VERY long time, then you want to stay at 20% or less discharge.)

    Okay, so I've decided on 25% max discharge for the batteries in my camper. I will use a battery monitor with a generator remote start relay so that when the batteries get down to 75%, the generator will start up.

    I've got about 400ah of storage, and the a/c will suck out about 50 per hour, so in as little as two hours time, the batteries will be down 25% and the generator will fire up. While it's running, it will run the a/c and charge the batteries. Once the batteries are charged, then the gen will shut off and two hours later the batteries will again be down 25%. Rinse and repeat.



    Now...why haven't I mentioned the solar? Because 245w isn't really enough to matter.

    Even though solar panels put out more than 12v, I'll just use 12 - again, to keep the math simple.

    245w / 12v = 20.4amps

    Now, if the camper is sitting in the sun instead of the shade, and if it gets say, 5 hours a day of decent sunlight, then that's about 100a of power generated that day.

    So...I can figure that for about two hours a day, the a/c will be running from power that the PV panels created.

    The rest of the time, the generator *WILL* be doing the on/off thing every couple of hours.



    Some things to consider:

    * The a/c compressor won't be running non-stop - so it probably will take a bit longer than 2 hours to drain the batteries 25%.

    * I don't know at this point how long the generator will have to run for the batteries to get charged up. Any decent charge controller will stuff a lot of power into the battery in a hurry, then as the battery fills up, the charger will taper off and go easy to bring the battery up that last bit for a full charge.

    For all I know, the generator will have to run for 4 hours to properly top off the batteries when they are 25% down. That would mean I'd be looking at a "2hr OFF/4hr ON" cycle.

    * The generator I'm planning to buy is a "Generac Impact 36G Plus" which I can get for a good price from a place in nearby Chula Vista, CA:

    http://www.advrv.com/generators.htm

    This generator comes with a separate inverter box which puts out Sine Wave instead of Square Wave. It also has a digital load-based throttle control. Basically, it's comparable to a Honda EU series for sine wave and fuel conservation.

    There are some interesting things in the spec sheet for this generator:

    http://www.generac.com/PublicPDFs/15971.pdf

    "LOADING RECOMMENDATION

    Generator designed to operate (1) 13,500 BTUair conditioner with 1,750 watt reserve base load. (Air conditioner should be equipped with easy start kit)."

    Easy start kit would be that extra capacitor that I mentioned earlier.

    "Fuel Consumption (gph/lb.ph)
    No load Half load Full
    Gasoline 0.14 0.32 0.54"

    The a/c is actually a pretty small load for this generator, but I've got to add in the battery charger as well so I'm guessing that it will run about about 1/4 load most of the time. The problem is that right now I don't know how long it will have to run to charge the batteries up from 25% discharged.

    This generator comes in a Propane model as well, which would probably be better for a permanent home installation, since you could hook it up to a Really Big Tank.



    Now, for your situation...

    Using the same a/c unit, to run it 6 hours a day from solar, you would need 3 times the battery capacity that I'll have - if you used the same batteries I'll be using, and you wanted them to live long and prosper so you keep them at 25% discharge or less - you would need 12 of them at ~$200 USD each = $2400

    You would need to generate 300ah/day from the solar panels to recharge the batteries. Optimistically figuring 5 hours a day of good sun - then you need to generate about 60 amps per hour, so you need about 720w of PV panels. Figure the absolute best price you will find on panels is $3/watt and you're looking at at least $2200 for the panels.

    Then you need the charge controller, and a battery monitor, and inverter...wire and fuses and mounting hardware and screws and goop and....you get the picture.

    Just the batteries and PV panels are going to run you $4600 + shipping. At the very least, you *might* get the job done for 6 grand if you do the work yourself.


    * BUT THAT IS JUST FOR THE A/C. What about the fridge?
    * This is all "best case" - good sun every day, cheap prices on the hardware. The reality is that once you start doing the "real math" the price is going to go up.


    I won't be living in the camper and probably won't be running the a/c 6 hours a day every day when camping/fishing/traveling.

    For the a/c it's really all about the gen. The solar/battery rig is really only there to A) save a bit on fuel when I do use the a/c, and B) eliminate the need for the gen when I don't use the a/c.

    I'm eventually going to replace the propane fridge with an electric, and the solar/battery setup will be more than enough for that.



    I would seriously look at doing your place like I'm doing my camper.

    * That gen will run both the a/c and a fridge and a few other things.
    * It comes with a sine wave inverter.
    * It's pretty quiet and as fuel efficient as the Honda EU that everyone is in love with.
    * Costs less than the EU3000i and puts out more electricity.
    * You can get it as an LPG unit and run it off a big house LPG tank.
    * For every 200w of solar panels that you add, you can cut down the run-time of the gen by maybe 2 hours a day - IF you have enough battery storage available.


    Also, take a look in the energy conservation section of these forums and check out the Sanyo Mini-Split thread. That might be a better way to go for a house.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    i was thinking of the eu3000 for if they already need up to the 2300w of their present generator, then you would be pushing things going lower in watts like for an eu2000. no need for multiple generators though in my opinion and keep the 2300w genny as backup or sell it.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Window A/C run on Solar

    I second Niel's recommendation of the Honda EU3000. Hondas are expensive, but they're also very efficient, very quiet, and very dependable.

    Don't get trapped by false economy of buying something cheap that you'll end up discarding when you up grade later. This goes for wire as well as generators. You can 'plug in' more panels, a different controller, additional batteries, or a bigger inverter if you've already got the wire size in place. Think long-term and think up-grading. It would be fairly safe to say all of us here have increased the size of our systems over the years, despite our constant vigil to conserve power.
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: Window A/C run on Solar

    I thought very seriously about the EU3000i for my camper, but I think I like the Generac instead for several reasons:


    * The Generac is cheaper (for the gas model, about the same if you get the LP model).

    * The Generac is designed to be built-in.

    * The Honda is a bit quieter - 58db @ full load - than the Generac - 65db @ half load. But it's not that much quieter, and most of the time I'll be running mine at 1/4 load.
    (EDIT: Actually, with the Generac built into an insulated box, it'll probably end up being quieter than the Honda @ 7m.)

    * The Generac is about 100lbs, the Honda 135 lbs.

    * The Honda has its own battery and fuel tank, the Generac uses the vehicle's. My truck has a 22g in the back and an 18g along the mid-line. I'll probably hook the gen to the mid (aux) tank. Running the a/c and charging the battery - using about .25g/hr - that'll give me up to 32 hours of gen run-time without refueling or touching the rear tank for the engine.
    (EDIT: WOOPS! 18x4=72 hours...NOT 32 hours)

    * They both use digital throttling for fuel economy. The Honda you have to turn on Eco mode, or else it runs at constant RPM like any other gen. The Generac is always in Eco mode.

    * They both put out sine wave power.

    * The Generac's continuous output rating is 3600w, the Honda's is 2800w continuous, with 3000 surge.

    * The Generac is designed to use a remote start.

    * The Honda is NOT more fuel efficient - the Generac is!
    BOTH of these gens use 0.32gph at 50% load - which is 1800w for the Generac vs. 1500w for the Honda. At full load the Generac uses 0.52gph (3600w) vs. the Honda using 0.49gph (3000w) at full load.


    So at least for me in this particular application - the Generac Impact 36G simply blows away the Honda EU3000is.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    hmmm. thinking-see smoke? do they have some inverter gennies that operate 1800 rpm to last longer yet?
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: Window A/C run on Solar
    niel wrote: »
    hmmm. thinking-see smoke? do they have some inverter gennies that operate 1800 rpm to last longer yet?

    ?

    The Impact 36g uses a digitally controlled stepper motor to throttle - it's not a constant speed gen. It's like the Honda in Eco mode.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Window A/C run on Solar

    stupid me of course they are variable, but i meant even more reliable low end rpm ranges, better construction, etc. you know the industrial or commercial quality gennies, but inverter types.
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: Window A/C run on Solar
    niel wrote: »
    stupid me of course they are variable, but i meant even more reliable low end rpm ranges, better construction, etc. you know the industrial or commercial quality gennies, but inverter types.

    Well, everyone is in love with the Honda and Yamaha inverter gens (don't get me wrong, I think they are great - I just have a need for something with the same features but also remote start and more fuel capacity), and the Chinese are knocking off copies as quick as they can.

    I think we're going to see a whole lot of new variable speed inverter gens in the future. Personally, I think they will probably end up being the standard and old style gens will fade away.
  • RandomJoeRandomJoe Posts: 464Solar Expert ✭✭✭
    Re: Window A/C run on Solar
    cswaite wrote: »
    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.

    I'll caution you on the HF panels, even that 45W rating is highly optimistic! I started with a set of them (and still use them) but the absolute best I ever got was 30W, that was the day I opened them and aimed them carefully at the July noonday sun. Best output on a regular basis while on the roof has been 20-25W. Others have seen similar numbers from them.

    So keep that in mind when sizing loads and estimating how much power you can draw from your battery. I found I was able to reliably replace 9AH per day in winter (depends on your solar insolation, of course). That really isn't very much power, when you start adding things up! Be careful not to overdo it and kill the battery.

    I replaced the HF controller pretty quickly with a better one from NAWS, the HF one just switches the panels on/off to the batteries. And mine did that at an undesirably high voltage - 14.8-15V, which is higher than I wanted the battery to stay for any length of time. The replacement does the three-stage charge pattern - bulk, absorption, float - and (I figure, anyway) keeps the battery much happier long term.

    The HF controller can still be useful as a power distribution unit, if you want.
  • cswaitecswaite Posts: 46Solar Expert
    Re: Window A/C run on Solar
    RandomJoe wrote: »
    I'll caution you on the HF panels, even that 45W rating is highly optimistic! I started with a set of them (and still use them) but the absolute best I ever got was 30W, that was the day I opened them and aimed them carefully at the July noonday sun. Best output on a regular basis while on the roof has been 20-25W. Others have seen similar numbers from them.

    So keep that in mind when sizing loads and estimating how much power you can draw from your battery. I found I was able to reliably replace 9AH per day in winter (depends on your solar insolation, of course). That really isn't very much power, when you start adding things up! Be careful not to overdo it and kill the battery.

    I replaced the HF controller pretty quickly with a better one from NAWS, the HF one just switches the panels on/off to the batteries. And mine did that at an undesirably high voltage - 14.8-15V, which is higher than I wanted the battery to stay for any length of time. The replacement does the three-stage charge pattern - bulk, absorption, float - and (I figure, anyway) keeps the battery much happier long term.

    The HF controller can still be useful as a power distribution unit, if you want.

    Thanks for the insight. I would like to test to see how much mine get. I have a multi-meter but dont know exactly how I would hook up the leads, and what setting on the meter? Any help.

    Thanks
  • BB.BB. Posts: 25,623Super Moderators admin
    Re: Window A/C run on Solar

    Google for DMM/digital multi-meter tutorial and read through those--something like this:

    http://mechatronics.mech.northwestern.edu/design_ref/tools/multimeter.html

    The maximum current for your panel will be less than 10 amps--so set your meter to 10amp maximum scale.

    WARNING--a single solar panel is pretty safe to mess around with... If you connect your meter wrong--either nothing will happen, you may pop a fuse, or destroy the DMM (rare).

    HOWEVER--Lead Acid batteries are a whole bunch of danger shoved in a plastic case... Connecting a DVM set to 10 amp scale placed on the battery can cause big sparks, white hot glowing wires, hydrogen gas explosions, and spraying concentrated sulfric acid around + chunks of plastic, lead, and copper.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoeRandomJoe Posts: 464Solar Expert ✭✭✭
    Re: Window A/C run on Solar
    cswaite wrote: »
    Thanks for the insight. I would like to test to see how much mine get. I have a multi-meter but dont know exactly how I would hook up the leads, and what setting on the meter? Any help.

    Thanks

    There are a few different ways, and with your meter you can put it in current mode then inline with the solar panels to measure the current. Change to voltage mode and measure battery voltage. Volts x Amps = Watts. As BB said, be careful! :)

    But I'm lazy. I also wanted something I could leave in over time, to see how things went, without spending a lot. The "real" battery monitors are a bit pricey for a system of this size. Since I had other uses for them (checking current draw for my ham radios and other 12V gear) the Watt's Up meters were the best deal. With just one, you can put it inline with the panels and it'll let you track volts, amps, watts, etc in real-time along with showing you cumulative amp-hours. Current measurement is one-way only, though.

    I have two, and hooked them up back-to-back off the battery and one showed charge current, the other discharge current. Thus I was able to manually track state of charge by comparing AH readings. Not perfect, but for a small system like that it worked.
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