More panels & window AC or efficient mini split AC?

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rrroae
rrroae Solar Expert Posts: 46 ✭✭
Would like to get opinions on the following.


We can either buy 4 205 watt Kyocera panels with pole mount which would double our current pv system and get a cheap 12,000 btu AC or we can get a 12,000 btu Mitsubishi mini split AC with a SEER of 20.5. Panels and pole will cost $3k delivered. Mini split AC will cost $2,600 professionally installed.




Our current setup is:

- 4 kyocera 205 watt 24 volt panels wired in series
- 4 Crown 6 volt 395 amphour batteries wired for 24 volt
- Magnum 4024 120/240 inverter
- Morningstar 60 amp mppt controller

According to the Morningstatr string calculator, I believe the extra panels would put me at my max panel configuration.

http://www.morningstarcorp.com/en/strings/calc.php?viewdata=1&app=yes&mode=&ModInput=Manufacturer&manufacturer=1&model=KD205GX-LP&ratedPower=&NOCT=&Voc=&TCVoc=&Vmp=&TCVmp=&Isc=&TCIsc=&Imp=&TCImp=&product=23&Vmin=24.4&Tmin=-5&TminUnits=0&Vmax=31.2&Tmax=60&TmaxUnits=0


We currently use about 60 amp hours a day. In winter we usually have to recharge with generator every 4-7 days

Comments

  • drees
    drees Solar Expert Posts: 482 ✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    If it were me, I'd get the extra panels - then you won't have to run the generator in the winter, too.
  • russ
    russ Solar Expert Posts: 593 ✭✭
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    Re: More panels & window AC or efficient mini split AC?

    The Mitsubishi seems to be a better deal long term - providing you are happy with the capacity. High SEER and quality equip - you can add on panels anytime.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,530 admin
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    Re: More panels & window AC or efficient mini split AC?

    I would get the Mitsubishi (or Sanyo--which has been verified here as being very off-grid friendly--you set it for A/C low and it will only use 300 watts maximum, startup/running/stopping).

    And, I would get just enough panels that you don't have to run the genset during A/C weather (depending on how much you use the A/C and where you live--you may be OK with what you have already).

    Obviously, insulating the heck out of the room(s) where the mini-split will be used (and double pane windows) will be a big help too.

    Assuming that the A/C makes your home much more livable during the summer (especially for the spouse--happy spouse, happy home).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,005 ✭✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Not sure you won't just be running the Genny in the summer.

    Could you run a smaller Ac in a smaller room?

    I had about 1000 watt array and ran a 5300 btu window AC, for 2 summers and it worked out OK, I have no backup and a smaller battery bank, but could run 3-4 hours on thermostat in energy saver mode each evening. Please note I built the cabin to run AC off solar, it's in the shade, 6" insulation in the walls, 9x15 interior area.

    I went out and added 300 watts of panels last year, and ran the AC most of the afternoon, which helped lower the temp of the thermal mass.

    In the end I think you'll want both...lol
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Got off the phone with Mitsubishi customer service and they said their 12,000 btu unit is variable speed and has a consumption range of 205-1,300 watts so I assume this unit is similar to the Sanyo except for the Seer rating which qualifies the Mitsubishi for the 30% federal tax credit.


    I am still wondering about the panels because they would probably negate most of our generator run time in winter. I'm also thinking they would run a 9-12,000 btu window ac if used mostly during full sun days.


    I have some other projects going on so money is limited right now so it's one or the other.
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    I would vote panels this year and a small cheap window AC. Then a a year or two go with the Mitsubishi or Sanyo. Just keep your eye on the federal rebates, who knows when things might change.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • BB.
    BB. Super Moderators, Administrators Posts: 33,530 admin
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    Re: More panels & window AC or efficient mini split AC?

    The other cost to look at is the generator itself... Most gensets are only fuel efficient if operated at 50% or more of output capacity (the Honda eu2000i family is pretty fuel efficient down to 25% of capacity).

    If you have a large genset and/or small battery charger that limits your genset loading--look at adding charging capacity or using a smaller genset to charge the battery bank (keep the larger genset for backup and to run your shop, etc.).

    Many people are probably spending 2x or more on fuel costs to recharge their battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?

    BB that makes me think of another alternative. We have 2 gas wells on our property so we could get a Generac 7,000 watt NG generator. I remember I had looked at them a couple years ago but they needed 240 volt power for the maintenance cycle(I believe that's what the installer said) and I didn't have my hybrid 120/240 inverter at the time. We get 200,000 cuft of free gas a year and use about 140,000 so I think we'd be fine.


    My concern would be these generators are made for backup power and not continuous use and anything with moving parts is not as appealing as a solar panel.


    Thoughts?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    rrroae,
    this is a bit of a catch 22 for you as you may have some problems no matter what direction you go in. assuming you are off grid then forget about a cheap 12k btu a/c unit. by your talk you are determined to have a/c this year so that leaves one good option and that is for the mitsubishi a/c. now once you've gotten it you won't be running it much from solar as it would tax your present system pretty badly. even putting aside the pv issues you will find that even with a full battery bank to start that in less than 4 hours of running it full bore you will have exhausted about 50% of your battery capacity and running this a/c unit on a genny for now may be a good stop gap answer until more pvs and batteries are available to you. throttling back on the a/c unit may save you some too as it need not be full bore, but it would still be time limited as i'm sure you sized your present pv/battery system for your present loads so any use of the a/c om your batteries will force a compromise to your other loads. i think it would be a doable balancing act until you can get the extra $ down the road for the extra pvs and batteries. consider more than 4 extra pvs for so you have more headroom on using the a/c unit and i am thinking without checking that this is also a heat pump which allows use in cooler weather for heating? (i didn't read on it that closely)

    edit to add:
    i see you posted while i typed. if you can use a lng generator then go for it as it need not be a continuous 24/7 use, but would allow at least the hottest or coolest time periods for up to about 1/4 of the day with no problem and no drain on your present pv system.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Pardon my ignorance (I am sure I can look it up) How much is 200k cu ft of gas? (answered my own question,, 1 cu ft=1020 btu, that would translate to ~2500 gallons of Propane if my (always suspect) math is anywhere near close. (Propane ~79k btu/gal)

    Makes one think about an absorption cooling system, like on a LP fridge. Seems like one could heat the Ammonia boiler (designed and sized properly) with natural gas. Not too efficient, but in some ways, perhaps more efficient net/net than running a generator and a conventional A/C system. Hmmm!

    In my inventive mind (you know the one, where everything is easy to make and works great!) you could use captured waste heat on the condenser for hot water, as well as from the flue vent making the net efficiency even higher.

    Tony
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?
    niel wrote: »
    if you can use a lng generator then go for it as it need not be a continuous 24/7 use, but would allow at least the hottest or coolest time periods for up to about 1/4 of the day with no problem and no drain on your present pv system.


    If I can find a good NG generator that has good reviews, I believe this would be my first choice. Looking at some of the Generac reviews though gives me pause.



    The beauty of the NG generator would be it would also take care of our winter needs and wouldn't cost us any additional money because of the free gas.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?
    icarus wrote: »

    Makes one think about an absorption cooling system, like on a LP fridge. Seems like one could heat the Ammonia boiler (designed and sized properly) with natural gas. Not too efficient, but in some ways, perhaps more efficient net/net than running a generator and a conventional A/C system. Hmmm!

    In my inventive mind (you know the one, where everything is easy to make and works great!) you could use captured waste heat on the condenser for hot water, as well as from the flue vent making the net efficiency even higher.

    Tony



    Oh I have all kinds of ideas but putting them to practical use is another matter.


    I had read an earlier thread here which touched on using an absorption cooling system and I gave it some thought but I'm just not sold on the practicality of it.




    An idea I was tossing around was using the water from our gravity spring and running it thru a car radiator and using a 12 volt battery to run the radiator fan. Our spring water is about 54' degrees so it seems logical. The only problem was I couldn't convince my wife that a radiator would make a good center piece in our family room.



    For myself, I think it's best to stick to more conventional means of AC by either using a generator or more pv to operate an efficient window unit.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Personally, I would steer away from generac units, only because I have not had the best luck with them. If you are looking for something virtually indestructible, at a reasonable cost, try to find an older 1800 RPM Onan CCK unit. These were dirt simple, will run thousands of hours on gasoline, are pretty quiet if housed well, and they can be had pretty cheap. They probably aren't the most fuel efficient units, but given your cost of fuel that isn't your first consideration.

    Most of the CCKs were in the 5 kw range, although they made a CCKB model that was exactly the same, but it ran at 3600 RPM, and put out 10 kw continuous duty. It doesn't have the life span the CCKs do but anytime you can run an engine at twice it's design RPM continuous rated and still run thousands of hours that's pretty good. I have an old CCKB and it still runs like new, and it must have 5000 hours.

    With natural gas fuel, you would have to derate a few 100 watts, but they would last forever. Even an old worn one, can be rebuilt fairly reasonably, and then run another 10,000 hours. (You can also often get them pretty cheap from people who don't know what they are really worth,,,$2-300)

    Here's a couple (I know the e-bay line will go away)
    http://cgi.ebay.com/Onan-5KW-Gas-Generator-Cart-Runs-Nice-RV-Camper-/220592402673?cmd=ViewItem&pt=BI_Generators&hash=item335c54f0f1#ht_3249wt_1005

    http://cgi.ebay.com/Onan-Generator-Pick-up-Indiana-/130384593834?cmd=ViewItem&pt=BI_Generators&hash=item1e5b8703aa#ht_500wt_1020

    http://www.smokstak.com/forum/forumdisplay.php?f=1

    There are some pretty smart folks here, who have lots of grease under their nails.

    Good luck,

    Tony
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?

    It could be a mistake If you don,t get the panels now that match the ones you already have. I went down that road twice. Got 8 panels and decided I wanted 12 more of the same. Couldn,t get them because they discontinued them So got 8 more from different manufacturer. decided later that I wanted 4 more of them and they were discontinued. What you might be able to do is at least get the panels that match the ones you have and forget about getting the mounts for now. Get the mitsubushi air and get the #30 % rebate on your taxes and put toward the polemounts next year. Most important to get the panels that match the ones you have as it is possible they could be discontinued. S:Dlarvic
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Good point about getting matching panels.



    Shouldn't I still be able to run an AC if I'm fully charged by around 1pm and buy an additional 820 watts of pv?
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
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    Re: More panels & window AC or efficient mini split AC?
    rrroae wrote: »
    Good point about getting matching panels.



    Shouldn't I still be able to run an AC if I'm fully charged by around 1pm and buy an additional 820 watts of pv?
    One of the more knowledgeable guys can tell you if the added panels will make this work. I got a new 110 volt mini split that qualifys for the 30% tax break ,but still need to get it installed. S:Dlarvic
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: More panels & window AC or efficient mini split AC?

    Found a more efficient Mitsubishi. Here's a 9,000 btu mini split with heat pump that the specs say runs at 25 SEER. Runs at 230 volts.




    http://www.mehvac.com/taxcredit/MSZ-FD09%C6%92p12NA_product-sheet.pdf






    Might go this route depending on what the installer will charge.