This SOLAR PLAN MUST be Possible>>

Treblig
Treblig Registered Users Posts: 23
Hi,

I live in South Texas, it's hot all the time. In the last three months it has rained twice and only scattered showers at that. The average temp for the last three month has been well above 85 (95 or better the last 30 days) and the real summer heat hasn't set in yet because August is usually our hottest month. I have a 4 ton unit on my house, recently I purchased a 5000 BTU window unit to keep the bedroom extra cool at night so is not to have to keep the 2400 sq/ft house at 66 degress to sleep comfortable at night. The 4 ton unit had been running 24/7 until I installed the 5K BTU. Around here the weather is so hot and humid (95%) that the AC has to run all day just to keep the house from getting so hot that it never cools down enough at night for comfortable sleep.
My solution - I want to get another 5K window unit to run on solar. Around here the electric company will give you $2 for every watt in solar that you purchase. Harbor Freight has their 45 watt panel (3 15 watt units) on sale for $179 with 20% off coupon it makes $144 minus $90 from the electric company come to $54 invested. Now I figure I need ten 45 watt assemblies (estimate) to run the 5K BTU unit which makes $540 plus tax and $129 for the AC unit. I'll need and inverter but I don't know what size?????
My plan is to run the small window unit on solar from 10 AM to 5PM each day (only during the day). The sun comes up at 6:30 and sets at 8:30PM. I don't want to have to use batteries if I don't need to. It will be a dedicated system running off grid just for the 5K BTU AC. AC specs are 4.9 amp, 515 cooling watts, 115 VAC. If I can keep my 4ton unit from turning on at least 50% of the time during the day by running the solar AC full time for 7 hours I think I would save about 20/30% on my AC bill. Night time is not a problem now that I have the small unit in my bedroom because I can keep the 4ton set on 73/74 (whole house) while I keep the bedroom at 64 degrees.
My questions:
1. Will 4500 watts of solar power start and run the 5000 BTU AC (9.7 seer) or will I need to start the unit on grid then switch over (flip switch) after starting (it will then stay on continuously all day).
2. I don't want to spend money on batteries because the unit will only be used during the hotest part of the day and never at night (and only during summer, March thru Nov).
3. Last month my bill was $300 (9.7 PerKH) if I can knock just $50 off that bill the whole shootin' match should pay for itself in about 20 months...is my math wrong, can it be done??
4. Now that I have the window unit in the bedroom I keep the 4ton set on 78 degrees during the day. So the new window unit should keep the 4ton from turning on as often..right?
5. I'm basically using the small (extra) window unit to run interference (using free electricity) during the day when temps run around 98/100 just about every day until September, there is no lack of sun here. If ten 45 watt panel won't do it how many would it take?
6. If batteries are used to run appliances when there is no sun then I don't need batteries for my puposes RIGHT??
7. What size/type inverter would I need?
8. I have good insulation and have recently had all attic ducts resealed, 4ton unit has been checked, condenser has been cleaned and evaporator checked.

I really want to do this I just don't know if I'm making the right assumptions..PLEASE HELP, I'm burning up here and it's only going to get hotter!! Any helpful suggestions/spec/data are appreciated.

Gil in Tex
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Do NOT waste your money on HF panels!

    Okay, now take some deep breaths of that horribly hot and humid Texas air.

    It is likely that your utility will pay $2 a Watt for an installed approved grid-tie system, not just any old purchase of panels. That would be a good thing, as it would off-set electric use regardless of what was using it.

    You might also want to seriously consider investing some time, effort, and money into evaluating your house as a whole to see where all that cooling is going. Lots of properly installed insulation, for instance, might be better economically than a few kilowatts of solar on the roof.

    The idea of installing solar just to run A/C, especially a window unit, has been bandied about here several times. It always comes up a loser because the units aren't very good on power. In that vein, take a look at the mini-split type of A/C: http://forum.solar-electric.com/showthread.php?t=5104

    But please, please do not go buy a bunch of cheap panels and expect them to power your A/C. You can not run an off-grid inverter without batteries, either.

    Oh, and welcome to the forum.
    Any other questions?
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    Thanks, but I did go thru many of the previous posts on this web site. None addressed a dedicated solar panel set up (off grid) for running a small AC unit (during day ONLY). I don't understand why I have to have batteries if I don't plan on running the unit when there is no sun. Unless i need maybe two or three to boost initial start up. What is the purpose of the batteries?? The mini-split has a heater (something I never need) ,I see that as a waste of money. We use our heater maybe two or three times a year. Please explain in laymans terms why I need batteries (how many). I don't mind buying a few but they would never be used. Was my math wrong? The fact that the small window units are not good on power doesn't matter if the power is free (after intial investment of $1000) with payback in 20 months. Most of the other posts claim that it's a bad investment because of all the batteries you have to buy and maintain to run with no sun. Are you saying that the ten 45 watt solar panels will not produce enough juice to power the 5000 BTU unit? Now if it takes 30/40 45 watt units then I might reconsider and even then payback would come in 3/4 years...still not bad. Can you show me the math on how many 45 watt units (using specs I gave) it would take to power the AC unit after intial start up? All installation will be done by myself and a friend who knows electrical so the cost will be only in parts.

    Gil in Tex
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    I know I personally have given this explanation before, but there's so many posts it could be impossible to find.

    There's two kinds of inverters: grid-tie and off-grid.
    Grid-tie inverters take whatever power the panels put out and feed it to the grid (and the household). No batteries involved unless it is a hybrid type with battery back-up.
    Off-grid inverters need batteries to run. No batteries = no operation. The reason being that panels put out a wide variety of Voltage and current depending on how much sun they're exposed to and how much load is put on them. Without the batteries to even out the power, the inverter can not supply a steady output Voltage with the ability to handle loads up to the rated maximum Wattage.

    Running even "small" window A/C's is a challenge. With the exception of the mini-splits mentioned, refrigeration has a very high start-up surge meaning you need a high Wattage inverter and batteries capable of supplying a significant amount of ready current just to get them started. Once running they have a healthy appetite for power too. This thread deals with exactly that issue: http://forum.solar-electric.com/showthread.php?t=11787 It wanders a bit and is very long, but the explanations are in there.

    For any off-grid design you need to know the maximum Watts and the total Watt hours per day. This is tricky with something like air conditioning because you never really know how much it will run. One of the biggest problems with off-grid is getting the balance right and the eternal desire to not waste potential Watt hours that don't get harvested once the batteries are full.

    Those who have the mini-split units love them. I'd say the heater is irrelevant considering the greater cooling efficiency.

    I also think that a grid-tie system would return you more value for your solar $ than a stand-alone set-up used solely for running A/C.
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Hey Gil...I am outside of Boerne in between Austin and San Antonio.

    You need the batteries to control/regulate the power to the inverter. The power is all over the place from the panels. Cloud goes over and the power drops to squat.....then shoots up to XXX amps. Think of the batteries as a big capacitor. Keeps the power consistent.

    Harbor Freight Panels, while looking inexpensive, are actually more expensive (per watt) than anything out there. As I found out the hard way :)

    But the short answer is yes you can run a small window unit on solar. You just have to size the system...and we can help you do that......but :)

    I have 5000 sq feet in a 2001 built house.....man my power to cool dropped like a rock when I installed roof vents in my roof. Then I added insulation.....ceiling fans in every room....a watt saved is much cheaper than a watt produced.......

    5000 BTU unit will pull about 11-13 amps at start up and run on about 7-7.5 amps. You are not going to flip a switch man.....aint gonna happen as the compressor will cycle throughout the day anyway....you cant be running to flip a switch...your not nanosecond fast enough. So you have to build to the peak power required and that would be about 13 amps lets say.
    13X12=156. So there is a minimum of 156 watts X how many hours your gonna run it. Lets say your gonna run it from 2pm till 7pm. so that is 156X5=780 watts.
    Factor in your losses of panel, sun efficiencies/wire loss and we are at a minimum of daily required 1000 watts for the 5 hours of AC run time required. So we gotta make 1000 watts minimum to run that bad boy 5 hours a day.

    If I had 2 Kyocera 135 watt panels (15 amps) I could generate 1K per day and I do myself.

    I would need a minimum of 240 amp hours of battery. 50% (never go below 50% of battery capacity) of 240 is 120 amp hours X 12 volts =1440 watts stored.

    You would need a minimum of a 2000 watt inverter to carry the compressor cycling on and off. 120X13=1560 watts.

    So my Texas math shows this...
    (2) 135 watts panels are on sale right now for $350 each plus shipping.
    (1) Controller...say a Morningstar 20 amp controller $100 bucks (I think)
    (1) 2000 watt inverter......shop around. Xantrex is probably gonna be your best bet. Maybe $250'ish?
    120 amp hour deep cycle batteries at WalMart in Boerne are $90 each.

    That is my math......
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    I totally agree with Cariboocoot! He is not steering you wrong, just trying to protect your own best interests. You asked the questions, Cariboocoot answered correctly.
    "The Only Sarge" also has some excellent points.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Sarge, there's a small problem with your math. It's the old "switch from AC to DC" thing. The air conditioner may draw 13 Amps - but that's at 120 VAC. On the DC side of things that more like 130 Amps. What's worse, 12 VDC isn't always 12 VDC. When you size things up you have to look at the Watts at the minimum Voltage, which is usually 10.5 Volts.

    Besides which I think you may find the start-up surge on one of these units will briefly exceed the 15 Amp normal max of a circuit breaker: they don't trip instantly (unless you live in Canada and have mandatory arc-fault breakers trying to run the bedroom A/C :grr ). In fact it may well exceed 20 Amps.

    The other user, sueco, already found her 580 Watt 5,000 btu A/C drew much more than the rating. A lot depends on which A/C you've got.

    In reality you'd probably need a 2.5 kW inverter, which is really too large to run on 12 VDC. This is not an absolute, okay? So don't everyone start jumping on the moderator telling him it can be done on less; without some absolute numbers on what the A/C will draw, including the surge, you can not be more specific.

    Using Sarge's 7 Amps running value you're looking at 840 Watts running. Assume a 50% duty cycle and you've got just over 10 kW hours per day. That is seriously large power. Needs nearly 1000 Amp hours of battery @ 24 Volts and around 3400 Watts of array to recharge. Rough estimates; not precise calculations.
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    Now we're talking!!! Both of you gave me some very helpful info. I am starting to agree with cariboocoot about the on-grid. I guess it wouldn't make a difference in the AC bill because the meter doesn't know if the power is coming from the solar or the grid?? Only with on-grid no batteries are needed...but then is there a drawback for on-grid?? I also understand about the batteries now..thanks.

    The Only Sarge also gave me some nice tidbits to chew on especially about solar panel prices...I must look into this further??? But you didn't tell me how many batteries (if I go that route)? I do have ceiling fans in every room and last year I put in an attic fan and installed numerous slotted vents in my eaves ( made the calculations for incoming/outgoing CFM from fan and gave it plenty of vents to draw from). So my attic is about 20/30 degrees cooler (running about 85 degrees on a hot day). I have a high efficiency 4ton 13.5 SEER so I'm doing all I can.
    Problem is I have all this sun and a continuous breeze from living near the coast...I hate to waste it!!!
    At Harbor Frieght I would pay $162 for 135 watts (after electric company rebate)..is that not a good deal or are the panels "cheaply made"? Or are the Kyocera 135 watt panels more efficient at $350?? 240 amp hours of battery isn't very much, is it??

    Waynefromnscanada...I believe everyone on this web site is willing to help. Cariboocoot is only trying to educate me..but I'm stuborn and if you're gonna shot me down you have to use logic, good data and creativity otherwise I'll keep asking questions until I realize that my ideas are no good. i just need to know what I can and can't do with respect to solar panels, batteries and 5000 BTU window units.

    Keep talking I'm listening!!!

    Gil in Tex
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Sarge, there's a small problem with your math. It's the old "switch from AC to DC" thing. The air conditioner may draw 13 Amps - but that's at 120 VAC. On the DC side of things that more like 130 Amps. What's worse, 12 VDC isn't always 12 VDC. When you size things up you have to look at the Watts at the minimum Voltage, which is usually 10.5 Volts.

    Besides which I think you may find the start-up surge on one of these units will briefly exceed the 15 Amp normal max of a circuit breaker: they don't trip instantly (unless you live in Canada and have mandatory arc-fault breakers trying to run the bedroom A/C :grr ). In fact it may well exceed 20 Amps.

    The other user, sueco, already found her 580 Watt 5,000 btu A/C drew much more than the rating. A lot depends on which A/C you've got.

    In reality you'd probably need a 2.5 kW inverter, which is really too large to run on 12 VDC. This is not an absolute, okay? So don't everyone start jumping on the moderator telling him it can be done on less; without some absolute numbers on what the A/C will draw, including the surge, you can not be more specific.

    Using Sarge's 7 Amps running value you're looking at 840 Watts running. Assume a 50% duty cycle and you've got just over 10 kW hours per day. That is seriously large power. Needs nearly 1000 Amp hours of battery @ 24 Volts and around 3400 Watts of array to recharge. Rough estimates; not precise calculations.

    I know I played loose with the numbers....but tried to be in the ballpark for example purposes Coot.....So wadda I get? A B- C+ what?!!!!
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    FYI - I currently have the exact 5000 BTU Ac running in my bedroom. What would it take to check the start up amperage, since I have the exact same unit that I plan to use in my solar panel plan I can get precise data. I don't think they give that info on line, even with the model number.

    Gil in Tex
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    Now we're talking!!! Both of you gave me some very helpful info. I am starting to agree with cariboocoot about the on-grid. I guess it wouldn't make a difference in the AC bill because the meter doesn't know if the power is coming from the solar or the grid?? Only with on-grid no batteries are needed...but then is there a drawback for on-grid?? I also understand about the batteries now..thanks.

    The Only Sarge also gave me some nice tidbits to chew on especially about solar panel prices...I must look into this further??? But you didn't tell me how many batteries (if I go that route)? I do have ceiling fans in every room and last year I put in an attic fan and installed numerous slotted vents in my eaves ( made the calculations for incoming/outgoing CFM from fan and gave it plenty of vents to draw from). So my attic is about 20/30 degrees cooler (running about 85 degrees on a hot day). I have a high efficiency 4ton 13.5 SEER so I'm doing all I can.
    Problem is I have all this sun and a continuous breeze from living near the coast...I hate to waste it!!!
    At Harbor Frieght I would pay $162 for 135 watts (after electric company rebate)..is that not a good deal or are the panels "cheaply made"? Or are the Kyocera 135 watt panels more efficient at $350?? 240 amp hours of battery isn't very much, is it??

    Waynefromnscanada...I believe everyone on this web site is willing to help. Cariboocoot is only trying to educate me..but I'm stuborn and if you're gonna shot me down you have to use logic, good data and creativity otherwise I'll keep asking questions until I realize that my ideas are no good. i just need to know what I can and can't do with respect to solar panels, batteries and 5000 BTU window units.

    Keep talking I'm listening!!!

    Gil in Tex

    Hey Gil....My only issue with on-grid is when the power is out I have no power....solar or grid. My battery bank is in a box in the shop so it is out of sight and safe. Grid power goes out I am still in business around here with lights/TV/Fans etc. No A/C though :)

    When I first started in this solar thing this year I bought Harbor Freight panels. I had 6 of them for 90 watts. On a good day they put out maybe 5 amps total all together. One Kyocera Panel puts out 6.5-7 amps by itself on the same day side by side. Rebates are the same for the Kyocera's and a 25 year warranty. Much better quality and results with the Kyocera has been my experience. But I am not in the solar panel sales business......so buy whatever you think is the best deal for you man.

    Solar Heads do not get all excited about A/C with Solar. Now you start a thread about heating up poop in a decomposing toilet and man you will get 'em excited for days. They would change their tune if they lived here in South Texas wouldn't they :)

    But Ol' Coot is right. Solar and A/C is a tough road...doable and possible...but takes quite a bit of panel etc. to do it. Hell look at a hard start kit to put on your window unit and drop those amps required to start that compressor.....work it out Gil!!!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Gil;

    Sounds like you've done all the right things with the house. Someone is bound to suggest adding reflective heat barrier, but how much that will do for you I don't know.

    A grid-tie system can sell energy back to the utility if there is any surplus and the utility allows this type of system. You'd have to contact them regarding their policy. You may also qualify for a federal tax credit on the install. So all told there should be money to help offset the capital investment and a reduction in your electric bill, whether or not the AC runs. You might want to play with PV Watts http://www.nrel.gov/rredc/pvwatts/ and see what kind of power you might expect in your area.

    The HF panels aren't very good quality. They may never put out anything close to the rated capacity. Kyoceras, on the other hand, have a long and solid reputation. If you go grid-tie you will be buying a lot of panels and may be able to get quite a good deal on a pallet load (as opposed to individual panel pricing). And no 240 Amp hours of battery isn't very much: @ 12 Volts it would be 1.4 kW hours at most.

    Sarge; we don't grade anyone on math around her - it would be too embarrassing for everyone. :blush:
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    FYI - I currently have the exact 5000 BTU Ac running in my bedroom. What would it take to check the start up amperage, since I have the exact same unit that I plan to use in my solar panel plan I can get precise data. I don't think they give that info on line, even with the model number.

    Gil in Tex
    Amp meter from Home Depot. Pay attention as it only peaks for a second or two and goes to run amps.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Once upon a time, I ran a evap. cooler (converted to a 12Vdc motor and pump) directly off a couple 75w solar panels with no controller or nothin. Worked great in my dry climate!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    FYI - I currently have the exact 5000 BTU Ac running in my bedroom. What would it take to check the start up amperage, since I have the exact same unit that I plan to use in my solar panel plan I can get precise data. I don't think they give that info on line, even with the model number.

    Gil in Tex

    Do yourself a really big favour and spend $30 on a Kill-A-Watt meter. Plug that window cooler in through it and have a look at the power consumption, especially over time. Have your cardiologist standing by. It won't catch the start-up surge though; doesn't sample fast enough. That requires some really expensive equipment. Manufacturers like to ignore that information.
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    Like I said before, I did some research before i started this thread because I've been on other sites for other types of information and read many similar threads by people who didn't bother to read a while before posting. I've read about soft-start capacitors (is that correct), and how they take the spike out of AC startup amperage. I'm I correct here?? That doesn't sound too expensive??
    I also read about the kill-a-watt meter and watched many on line videos on setting up solar panel etc. before starting this thread. Would a soft start gizmo make it more possible to use the solar panels to run the Ac unit (less batteries?). Panel prices have really come down over the years...I've been watching and waiting to pounce!!

    Gil in tex
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    Google Hard Start Kit...yes it will reduce the start up power required...basically it is just a capacitor with a relay.....
  • The Only Sarge
    The Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Coot wrote:
    Sarge; we don't grade anyone on math around her - it would be too embarrassing for everyone.

    Well bummer...I am having a bad day here Coot.....haven't bought headers in years...the headers on my 08 Silverado gave up the ghost so I ordered a new set from Summit today.....holy cow! We are in the wrong business man.....
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Well bummer...I am having a bad day here Coot.....haven't bought headers in years...the headers on my 08 Silverado gave up the ghost so I ordered a new set from Summit today.....holy cow! We are in the wrong business man.....

    Bad days happen to good people. If you can keep the number down to less than 365 per year you're doing the best you can.

    At least you have an '08 Silverado; I have a '92 E250. I found out tonight our Gov't is hiking gas another 5 cents per litre for the carbon tax. Don't let anyone ever tell you a carbon tax is good for the environment: the van pollutes just as much as ever, it just costs more to do it now. :grr

    BTW, American friends: gasoline here is now $5.35 per gallon US. :cry:
  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    $3.22 gal as of this post in east tennessee :D
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    i found this site is nice to check on pricing, but you need the zip code to do it. it doesn't extend beyond the u s though.
    http://www.automotive.com/gas-prices
    for those wondering about the zip code that pops up in it, it's not my zip code.;)
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    So am I correct by saying that it is cheaper and smarter to simply buy some PV panel and hook them up to the grid and benefit from the decrease in my electrical bill RATHER THAN going off frid with another window unit? Or as everyone seems to think...it's simply cheaper to get the low rate (9.7 per K/H) and not worry about harvesting solar power? If the later is the case, what is the purpose of this site?
    I'm being practical/realistic here, one of these paths has to be the best or smartest or most economical. I thought that it cost alot to get hooked-up to the grid (professional electrician costs)?? I'm going to pull my electric bill today so you can see what my usage comes to.

    Gil in Tex
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    You need to figure out your ROI for your situation. No one here would try and steer you to solar unless it makes some financial sense. If you are looking to lower you cooling costs alone, check out the mini split systems. If you think your electric rates are too high or going up take that into account. If going green means something to try and place a value on that.

    For us all of the above were considered, we have two 3 ton units here and last month we only bought $10 of off peak generation. With our carry over from last years utility year end buy back we have yet to send a payment to the utility. We upgraded almost ever aspect of our usage to minimize our usage before we bought solar. With utility rebates and federal and state tax credits our ROI is right around 5 years.

    PS my wife is a green, I am a capitalist and those views did not conflict in our situation.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    Thanks, but I did go thru many of the previous posts on this web site. None addressed a dedicated solar panel set up (off grid) for running a small AC unit (during day ONLY). I don't understand why I have to have batteries if I don't plan on running the unit when there is no sun. Unless i need maybe two or three to boost initial start up. What is the purpose of the batteries?? The mini-split has a heater (something I never need) ,I see that as a waste of money. We use our heater maybe two or three times a year. Please explain in laymans terms why I need batteries (how many). I don't mind buying a few but they would never be used. Was my math wrong? The fact that the small window units are not good on power doesn't matter if the power is free (after intial investment of $1000) with payback in 20 months. Most of the other posts claim that it's a bad investment because of all the batteries you have to buy and maintain to run with no sun. Are you saying that the ten 45 watt solar panels will not produce enough juice to power the 5000 BTU unit? Now if it takes 30/40 45 watt units then I might reconsider and even then payback would come in 3/4 years...still not bad. Can you show me the math on how many 45 watt units (using specs I gave) it would take to power the AC unit after intial start up? All installation will be done by myself and a friend who knows electrical so the cost will be only in parts.

    Gil in Tex
    The (very) short answer is that it doesn't work that way.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    So am I correct by saying that it is cheaper and smarter to simply buy some PV panel and hook them up to the grid and benefit from the decrease in my electrical bill RATHER THAN going off frid with another window unit? Or as everyone seems to think...it's simply cheaper to get the low rate (9.7 per K/H) and not worry about harvesting solar power? If the later is the case, what is the purpose of this site?
    I'm being practical/realistic here, one of these paths has to be the best or smartest or most economical. I thought that it cost alot to get hooked-up to the grid (professional electrician costs)?? I'm going to pull my electric bill today so you can see what my usage comes to.

    Gil in Tex

    gil,
    it may be cheaper to use a gt system than to go off-grid. off-grid involves the extra cost of the batteries and controller(s). one has to put it all out on paper for what they may want in either case and weigh it for themselves. do know that just because you may have an off-grid setup does not mean it isn't inspected and that would vary by region or area on what they require. off-grid systems can still cause fires and loss of life even though you don't have quite the power possibility as with the grid being there.

    as to this forum we like to think it's to help and possibly educate people on some of the ins and outs of solar in particular, even though we are open to all re sources. our purpose is not to sway everybody to get away from their utility electric or to stick it to the man even though there is some gratification in being able to do so. solar is expensive so we try to be realistic about it, but you can do things whatever way you want to and as long as you weigh things out in your mind and know the advantages and pitfalls of every option then go for it in whatever capacity you wish. there is no single answer we could give to you as we offer opinions and advice. you make the final determination on what to do for you.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    ggunn wrote: »
    The (very) short answer is that it doesn't work that way.
    Another answer with a few more words, would be to go ahead and buy the panels, have your "friend who knows electrical" do said electrical, save further frustrating those here who have been trying to help you, and learn the hard way that your vision of your desired installation will not work. Period.
  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    ggunn wrote: »
    The (very) short answer is that it doesn't work that way.

    agreed .. for a 500 watt window shaker, stand-alone solar powered i would think probably 12 of those panels .. about 4 - 215AH batts .. 1000 or so pure sine inverter and it would do pretty good on a sunny day and maybe a couple hours in the eve .. i would guess one could get 4-5 grand into that real quick .. it would be neat, but you aint going to save money .. only reason i made a system alittle larger than that is to be sustainable offgrid in an extended emergency but im alittle nuts :p
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    So am I correct by saying that it is cheaper and smarter to simply buy some PV panel and hook them up to the grid and benefit from the decrease in my electrical bill RATHER THAN going off frid with another window unit? Or as everyone seems to think...it's simply cheaper to get the low rate (9.7 per K/H) and not worry about harvesting solar power? If the later is the case, what is the purpose of this site?
    I'm being practical/realistic here, one of these paths has to be the best or smartest or most economical. I thought that it cost alot to get hooked-up to the grid (professional electrician costs)?? I'm going to pull my electric bill today so you can see what my usage comes to.

    Gil in Tex

    I've had my coffee now. You cannot run your A/C with just modules and an inverter; to run it off the grid you'll have to get a different (generally more expensive per Watt) inverter and a bunch of batteries, which will cost you more than what you are paying the utility company for the power to run that unit, even over the long haul, because you will have to replace the batteries and most likely the inverter as well long before the system has paid for itself. A common misconception held by many newcomers to solar is that in an off-grid AC system you EVER run directly off the solar modules alone. In an off grid system you are ALWAYS running off the batteries; the only purpose of the solar is to keep the batteries charged.

    If you have the grid accessible and it is dependable, it is virtually never financially advantageous to run anything AC powered off-grid. What may work for you, however, is to get a grid tied system to supply current to your home (and to the grid when your production exceeds your usage) to offset your electric bill, but there are a lot of things to consider before making that leap.
  • Treblig
    Treblig Registered Users Posts: 23
    Re: This SOLAR PLAN MUST be Possible>>

    OK, this is what I found on soft start capacitors. If I use this method does it make my paln more doable?? I won't need as many batteries or as many panels??

    Gil in Tex

    ***************
    In general, there are two reasons to use a soft starter: the power distribution network may not be able to handle the inrush current of the motor and/or the load cannot handle the high starting torque. As a rule of thumb, a motor utilizes around 600-800% of its full load current (FLA) to start. This current is referred to as inrush current or locked-rotor current. If a large motor is on a smaller power distribution network or on a generator system, this inrush current can cause the system voltage to dip, or to “brown out”. Brown outs can cause problems with whatever else is connected to the system, such as computers, lights, motors, and other loads. Another problem is that the system may not even be able to start the motor because it cannot source or supply enough current. Most industrial businesses run during the day can be fined or charged extra (Peak Demand charges) during this peak usage time for large transients caused by large horsepower (HP)/Kilowatt (kW) motor start ups. These Peak Demand charges can add up very quickly, especially if the motor needs to be started multiple times during any given day. The inrush current can be controlled one of two ways with a soft starter: either with a current limit (discussed later) or reduced linearly with the reduced voltage, and follows this approximation:


    Applications such as conveyors may not be able to handle a sudden jolt of torque from an across-the-line start. Utilizing soft starters reduces the wear and tear on belts, conveyors, gears, chains, and gearboxes by reducing the torque from the motor. The torque decreases as a square of the reduced voltage, and follows this approximation:


    Since soft starters are generally controlled and monitored by a microprocessor, a soft starter can add many features and protections fairly easily. It can offer a choice of the starting time, limited speed control, and energy savings. Power monitoring, such as three-phase current, three-phase voltage, power, power usage, power factor, and motor thermal capacity usage, can be implemented with current transformers, a voltage meter, and an internal clock. With the above implementations, protection, for the motor or the soft starter, from the items listed below (Table 1) can also be offered by stopping the firing of the SCRs, dropping out the bypass contactor (a contactor that carries the motor load after the motor is up-to-speed), and/or alerting a user via some form of communications with the microprocessor and another computer.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>
    Treblig wrote: »
    OK, this is what I found on soft start capacitors. If I use this method does it make my plan more doable?? I won't need as many batteries or as many panels??

    To build an off grid PV system to run your A/C is certainly doable. To build one that will run your A/C cheaper than power from the grid (@9-10 cents per kWh) isn't. Ye cannae rewrite the laws of physics, Cap'n! ;^)

    With starting caps you do not lower your energy consumption, all you do is spread the starting surge over a longer period so the peak current is not as high. It's a loan that you must pay back, and since no system is lossless, there is interest on the loan.
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: This SOLAR PLAN MUST be Possible>>

    I have an off grid system that runs two 2 1/2 ton central A/C units. They are set up up in two zones to provide redundancy.

    The four SW 5500 watt inverters easily start and handle the compressor surge helped in part by highly energy effficient variable speed air handlers and dual stage compressors. With the compressors running on the high stage, I've never seen the inverters operating above 16 amps with about 11 amps the norm for lower stage.

    Second, on overcast humid days lasting more than a week the back up generator might run about a couple hours in the morning as storage declines over a few days but I've never seen it run more than 20 hours or so the entire summer.

    Key point here is you have to have an adequately sized battery bank to run the A/C overnight. If you don't balance the panel array and battery bank size efficiently you'll either run the generator too long and/or you won't have enough starting power to run the compressors.

    A/C is not a problem if you size your system properly.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers