Wish to run my Room Air-Conditioner on solar during day time

Am thinking of using solar power to run my room Air Conditioner during day time.

Have a 18000 BTU ( 1.5 tons ) split air-conditioner runs on 220V AC, 50Hz. At start it draws a 30Amps current for few milliseconds, and then it comes to 12 Amps for few seconds, and then after say 15 to 20 seconds its current requirement comes to 8 Amps.

My idea is to find some soft-starter or a VFD ( Variable Frequency Drive ) so that I am able to nullify the starting torque current of the air-conditioner. And after its installation, I hope then I just have to worry for 8 Amps regular current requirement only.

This 8 Amps of current needed makes power requirement of my A/C 1800 Watts.

If I install solar panels of 2500 Watts, and a MPPT charge controller , then I guess, that I be able to have sufficient power to run my A/C during day-time for 6 to 7 hours.

Now I come to question about battery costs. This cost is high, and I wish to by-pass this cost.

Upon installing a Soft-Starter / VFD to the air-conditioner. And having 2500 Watts panels, a MPPT controller, and an off-grid Inverter ( no batteries connected ). Would I be able to run the Air-Con during 5 to 6 hours a day ?

Please comment on the above.

Regards.

Omar

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,728 admin
    Re: Wish to run my Room Air-Conditioner on solar during day time

    Welcome to the forum Omar.

    Guessing that you are from around Lahore Pakistan, and using the Solar Electricity Handbook to see "how many hours of sun" per day you get:

    Lahore
    Average Solar Insolation figures


    Measured in kWh/m2/day onto a solar panel set at a 73° angle (from vertical--or 17 degrees from horizontal for summer use):
    (Optimal summer settings)

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    4.13
    5.14
    5.94
    6.63
    7.18
    6.96


    Jul
    Aug
    Sep
    Oct
    Nov
    Dec


    5.96
    5.71
    5.92
    5.91
    5.01
    4.21


    You have some good sun, but also summer monsoons(?) that limit solar collection...

    The problem is that off grid solar power (solar panels + charge controller + battery bank + AC inverter) is pretty expensive power... In the US, we typically pay around $0.10 to $0.30 per kWH and off grid solar power costs around $1-$2+ per kWH (cost of equipment, installation, new batteries every ~5 years or so, new controllers/inverters every 10+ years, etc.).

    Using a VFD to limit the starting surge of your A/C is a very good plan. In fact, see if you can find any "inverter" mini-split A/C (or heat pump if you can use winter heating too) systems. There was an older Sanyo unit that would run on low speed/power at 300 Watts (and no starting surge):

    Sanyo Mini-Split AC


    Sanyo was purchased by Panasonic and many of the (very nice) Sanyo products "went away". But Fujitsu, Panasonic, and others still make some nice mini-split inverter A/C systems still (I believe). Of course, you have to find something local to Pakistan (guessing that is where you are from).

    The batteries are always going to be a limiting and costly factor with off grid solar. If you can reduce the surge current to near "running" current, that will be a big help. It will still be an issue though running AC during the day from solar+charging the batteries.

    Lead Acid batteries actually "like" to be cycled (discharge by ~25% or so at night and recharge during the next day). Running an A/C system during the day and having a battery bank to charge is a "questionable" setup to figure out the "optimum" way of doing this.

    For the sake of giving you a starting point... Say you assume the days you need A/C, you have at least 5 hours of sun per day, run the A/C at 1,800 Watts, and have a "minimum" sized battery bank to run the A/C for 4 hours without sun (and discharge the battery bank to 50% of capacity--Or C/8 discharge rate).

    The size of solar array to "break even" would be:

    1,800 watts * 7 hours per day * 1/0.52 system eff * 1/5.0 hours of sun per day = 4,846 Watt array minimum

    A C/8 battery bank capacity would be:

    1,800 Watts * 7 hours * 1/0.85 inverter eff * 1/24 volt battery bank = 618 AH @ 24 volt battery bank (C/8 rating)

    If you get C/20 Rated batteries, roughly:

    618 AH * 1.2 Peukert factor (wild guess) = 742 AH @ 24 volt battery bank

    The above are probably conservative numbers--You might be able to reduce them some (by 20% or so)--But it is a starting point.

    Does the above (assuming +/- 20-30%) make economic sense to you?

    You could possibly cut the battery bank capacity by 1/2 -- But I am not sure how long it would last. And you will have to be sure to only run the system when the sun it up and bright. By something like 4pm, you would have to turn the A/C down to low (or even off) to prevent damaging the battery bank with too much current draw.

    There is another alternative--Grid Tied solar (solar panels + GT Inverter). The GT system will power your local AC loads and even "push" power back into the grid (and even turn your power meter backwards--if it is designed that to run "backwards").

    With GT Solar--The Utility Power looks exactly like a giant "AC Battery"--Your system literally behaves as if it is "recharging" your utility power. It is "cheap" (no battery, no battery losses), and reliable (no batteries or "extra" components).

    GT solar "net metering" is common in many places in the US, but may not be common (or even legal) in your region.

    It is difficult to "save money" with Off Grid/Battery Backed solar power unless you have very expensive utility power (remote location with long power lines) or unreliable power (afternoon power failures and you need battery power for a few hours most evenings).

    If you wish to save money, typically conservation is your best first step. Lots of insulation, awnings over your windows. Trees to shade the roof/walls. Double pane windows to keep heat out, etc. all are usually better investments vs just installing off grid solar power.

    All wild guesses at this point--Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: Wish to run my Room Air-Conditioner on solar during day time

    Like Bill said, you need more like 5000w of solar panels (minimum). And even then, it is only going to work in the daytime, full sun.
    It is NOT going to save you money trying to move it to solar (off-grid).
    Even running a small 5000BTU window AC requires quite a bit of solar and batteries. I know because I do that.

    But if you grid-tie, then perhaps in 7-10 years it will pay for itself and you will be able to run it all the time.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • praful1303praful1303 Registered Users Posts: 1
    The running current of a 1 ton inverter ac is 5.3A. What would be it's starting current?

    Can it run on 2000watt PV panel with MPPT charge controller in day time with full sun?
  • BB.BB. Super Moderators, Administrators Posts: 30,728 admin
    Praful,

    I suggest that you create a new discussion (thread) telling us a bit more about your needs (120/240 VAC, Mumbai India or similar?, Hours a day of operation, etc.).

    In general, Inverter based A/C systems do not really have much (if any) surge current. They typically start/run at maximum cooling with the same maximum Current (Amps, Watts).

    Assuming the A/C system uses a standard Utility Plug, you can get a plug in energy meter (Watts, Amps, Watt*Hours, etc.) for not too much money.

    https://www.amazon.in/s?k=kill+a+watt+meter&ref=nb_sb_noss_2

    Accurate measurement of your energy usage is critical to planning an off grid power system... It is very common for the total cost of solar energy (initial purchase of equipment, replacement of batteries/etc. over time, etc.) to cost 5-10x+ the cost of local utility power.

    Off Grid Solar+Battery power systems are not cheap...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    The running current of a 1 ton inverter ac is 5.3A. What would be it's starting current?

    Can it run on 2000watt PV panel with MPPT charge controller in day time with full sun?
    No way to tell its starting current.  Every compressor is different.

    Can you run it with 2000W of solar?  Well, the term "charge controller" implies a battery, so provided you design it to cover both surge and operating current, and choose a battery wisely, it will run it for some time at least.  5.3A of running current, assuming 240V, is about 1200 watts, but your inverter may have to supply more than that depending on power factor.  A 2000 watt STC rated array will give you about 1500 watts under average conditions, so you'll have enough to carry the load at least in the middle of the day.  I would guess you'd get 4-6 hours of operation a day om sunny days.

    As Bill mentioned it will be VERY expensive.
  • mcgivormcgivor Solar Expert Posts: 3,437 ✭✭✭✭✭
    Running an air conditioning unit without battery support would be difficult because even though a large enough array may cover the needs most of the time, a passing cloud will cause a collapse in the supply.

    This is something that I take advantage of during the hottest period of the year, albeit with an inverter type split air conditioner of half the cooling capacity set at 30°C in economy mode. The running wattage is around 500W the array is 1800W, the battery capacity is 400Ah which is more than sufficient to cover the odd cloud. The battery capacity could be significantly reduced if lithium batteries are used due to their inherent ability to supply high current without voltage sag. The problem is the fringe periods when the PV output is lower than the demand as well as not having the capacity to recharge the battery if needed.

    Personally I wouldn't entertain tackling a project without battery support, in my case I'm using surplus energy that would otherwise go unused so a very different challenge, additionally even inverter based air coditioners are not created equally, the higher SEER rated are significantly more energy efficient.

     
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • jonrjonr Solar Expert Posts: 1,379 ✭✭✭✭
    In my opinion, you are better off getting an air to water heat pump and using PV solar to chill a large tank of water.   Use fan coils to cool from this, so minimal battery is needed.      An alternative is a solar AC.

    https://www.hotspotenergy.com/solar-air-conditioner/
    https://www.chiltrix.com/solar-chiller-applications.html

    The right way to know startup surge (an issue with non-inverter compressors) is to measure it.  

    I am available for custom hardware/firmware development

  • softdownsoftdown Solar Expert Posts: 3,338 ✭✭✭✭
    jonr said:
    In my opinion, you are better off getting an air to water heat pump and using PV solar to chill a large tank of water.   Use fan coils to cool from this, so minimal battery is needed.      An alternative is a solar AC.

    https://www.hotspotenergy.com/solar-air-conditioner/
    https://www.chiltrix.com/solar-chiller-applications.html

    The right way to know startup surge (an issue with non-inverter compressors) is to measure it.  
    Sounds like that will add moisture to the environment? 

    A constant challenge in every scenario - so many unknowns that are needed to make an education decision. But the constant factor remains - off grid power is very expensive unless one finds extra ordinary bargains. Those bargains are often very hard to find. May present compatibility problems when the various bargains are "patched together". Like my batteries that sat for years before my present solar array became functional. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • jonrjonr Solar Expert Posts: 1,379 ✭✭✭✭
    > Sounds like that will add moisture to the environment? 

    A closed tank/system doesn't and in fact both systems remove moisture (typically an important part of AC).

    I am available for custom hardware/firmware development

  • softdownsoftdown Solar Expert Posts: 3,338 ✭✭✭✭
    jonr said:
    > Sounds like that will add moisture to the environment? 

    A closed tank/system doesn't and in fact both systems remove moisture (typically an important part of AC).
    Know of a good simple primer? Sounds interesting.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • jonrjonr Solar Expert Posts: 1,379 ✭✭✭✭
    Most of the Chiltrix information is pretty good and relevant.  But no other ideas.

    I am available for custom hardware/firmware development

  • jtdiesel65jtdiesel65 Solar Expert Posts: 145 ✭✭✭

    I run an 1.5 ton AC unit.  I installed a soft start on it which dropped start up to ~6.1A ( measurements here https://forum.solar-electric.com/discussion/comment/288448#Comment_288448 ).  I also run a 6000 btu window mount AC that I run in the building that houses the battery, inverters, etc. I leave this on all summer.  No problem running both on sunny days with 4120w array. But I have a battery.

    I would think that this configuration would decrease the lifetime of the AC unit since it's going to have it's power cut every time a cloud covers the sun. Maybe there are no clouds where you live.




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