Undecided on Charge Controller

JaugJaug Registered Users Posts: 8
My first post so be kind!

This is what I have so far, two 160 watt panels. I plan to buy golf-cart battery's at Sams. I am planning on a 24 volt system.

I live in the woods we only have electricity for utility. We lose the grid often. So I would like to be able to run a few lights a computer and router during a outage. In between the power outages I will place a couple solar outlets for lights and router and or computer. I do realize I will need a inverter.

You all do not have to scold me on the following lessons:

Size your system to your needs. I will size my needs to the system. I know not too bright.
Only let your battery bank discharge 20%.
Using a watt meter to see how many watts each item will need.
I do know solar is considered not the best back up.....but if I can not make it the 10 miles or so to the closes gas station, plus not wanting to store a lot of gas, for a generator. Did I mention that I have to drive a mile or so through thick woods to reach the Black Top?
I also have read all the warnings about cheep mppt chargers.
And yes I am not really sure about everything I am doing...am willing to learn.

So I am back to the same question every Newbie has asked here....Charge controller.
I would like to have a 40-60 amp mppt controller....I can not afford top of the line (outback Apollo Blue Sky).
I would like to be able to add more panels eventually to my system also. I had hoped that the new Rogue coming out might fit my budget (tops $350) and also what I would want. The new Rogue is not available yet.

Now this is where I would like some advice....
Should I go with a proven pwm controller like:

TriStar 60 Amp 12/24/48 Volt Solar

Or should I go with something like this:

40A MPPT Tracer 4210R Solar Charge Controller Panel 12 24 V Remote LCD Display
http://www.ebay.com/itm/150998668307?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Maybe wait and see if the Rogue might be close to my price range?

Thank you for any thoughts or ideas that might be helpful.

Best Regards,
Jim

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Undecided on Charge Controller

    Welcome to the forum Jim.

    And, I am going to drag you kicking and screaming back to your loads. :roll:

    You are designing a pretty large system (at least from the solar side) with a 60 amp charge controller and a 24 volt battery bank. You could probably run the whole cabin off that system and get rid of your Grid power... But that is not what you were asking for. Backup power for a bit less money.

    I will suggest we start with a "smaller" system and see if it meets your requirements.

    First, a laptop computer may use ~30 watts, a router less than 10 watts, and a few (LED) lights for another 45 watts (5 fixtures with 9 watt bulbs). That adds up to around 85 watts continuous power. For such a system, I would highly suggest the MorningStar 300 watt TSW 12 VDC input AC inverter. I don't think you will find a better bang for the buck inverter out there that includes a couple of power save features (low power, a standby power option, and a remote on/off 12 vdc input). You would pay a lot more money to find a similar (smaller) inverter that would run on a 24 or 48 volt system.

    I do not love 12 volt battery systems, but for smaller power needs--It usually just makes sense to go 12 volt.

    So--Lets say you want to run the system around 8 hours per day (computer should average closer to 20 watts of power--but anyway...). 1-3 says of power storage, 8 hours of use per day, 50% maximum discharge, and pick 2 days of storage (nice balanced system):
    • 85 watts * 8 hours * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days of no sun * 1/0.50 max batt discharge = 266 AH @ 12 volt battery bank

    For a backup system--I probably would go with 2x 6 volt * ~220 AH golf cart batteries.

    Next, if I design this for pure off grid use--I would suggest a 5-13% rate of charge for the solar array based on battery AH capacity:
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 207 watt minimum array
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 414 watt nominal array
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 539 watt "cost effective maximum" array

    And sizing the array based on your amount of sun using PV Watts and assuming you are in south central Arkansas. Use fixed array tilted to latitude. Assuming Shreveport is closer to you, I get:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.70     
    2      4.53     
    3      4.97     
    4      5.47     
    5      5.57     
    6      5.81     
    7      5.84     
    8      6.02     
    9      5.56     
    10      5.50     
    11      4.00     
    12      3.77     
    Year      5.06      
    

    Assuming 4 hours of minimum sun (toss out the low months), based on using:
    • 85 watts * 8 hours a day = 680 WH per day
    • 680 WH per day * 1/0.52 system efficiency * 1/4 hours of sun per day minimum average = 327 Watt array minimum

    So, your choices run from 207 to 539 watt array based on battery capacity and at least 327 Watt array to run your loads for 9+ months a year without using a genset (in average weather conditions).

    And, you should be looking at a 20-50 amp AC charge controller. A 20 amp charge controller will run on a Honda eu2000i. A 40+ amp charger should run on a Honda eu2000i -- Both very fuel efficient gensets (if you want backup to your back power). The eu2000i should be able to run your refrigerator plus some other loads. The eu1000i (900 watt) may be a bit small

    Given that you have grid power, your choice in solar array runs from zero to around 539 watts (I am using all digits so you can see where I get the numbers from rather than just saying ~500-600 watt array).

    I will stop here. Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Undecided on Charge Controller
    Jaug wrote: »
    This is what I have so far, two 160 watt panels.
    <snip>
    I would like to have a 40-60 amp mppt controller....I can not afford
    <snip>
    Should I go with a proven pwm controller like:

    What is the Vmp of your panels? A PWM controller will be very inefficient if your panels are not of the correct Vmp for your system voltage.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • JaugJaug Registered Users Posts: 8
    Re: Undecided on Charge Controller

    Hey BB. thank you for getting back to me so fast. You gave me a lot to digest and to think about. Give me a little bit to let it sink in.

    Thank you Vtmaps for pointing that out. Here is how it is written on the back of the panels:

    ICO SPC - 160 watt
    Pmax 160
    Vpm 21.45 v
    Ipam 7.46 a
    Voc 25.91 v
    ISC 8.01 a

    I do believe the Vpm should be Vmp. (China)
    A PWM controller will be very inefficient if your panels are not of the correct Vmp for your system voltage

    Please do tell me how I would know.

    Thank-you very much.

    Best Regards,
    Jim
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Undecided on Charge Controller
    Jaug wrote: »
    Hey BB. thank you for getting back to me so fast. You gave me a lot to digest and to think about. Give me a little bit to let it sink in.

    Taking a breath and thinking about solar and your loads (conservation) can save you a lot of frustration and money.
    Pmax 160
    Vpm 21.45 v
    Ipam 7.46 a
    Voc 25.91 v
    ISC 8.01 a

    I do believe the Vpm should be Vmp. (China)

    These panels are not too bad... For charging a 12 volt bank we look at Vmp ~17.5 to 18.6 volts or so as "100% efficient match" for use with a PWM controller. For 24 volt battery banks, 2x Vmp, etc...

    So, efficiency of a "non-standard" solar panel would be around:

    ~18.0 volts Vmp-batt / 21.45 volt Vmp-panel = 0.84 = ~84% efficient vs a "standard" 12/24 volt Vmp-array on a PWM controller. So your 160 Watt panel * 0.84 would be have like a 134 watt panel...

    That is not too bad of difference--So I would not suggest paying $200-$300+ more for a good quality MPPT charge controller to make up that "missing" 16% from your array.

    If you choose a 12 volt system and purchase one more 160 watt panel for use on a 30 amp PWM charge controller vs buying a MPPT controller for $250 or more--Where do the chips land...

    To add to the confusion, an MPPT charge controller is usually going to have a lot more logging/computer interface options and more control of the charging parameters--Is this something that you "want to play with" and worth the extra costs for the extra computer processing power/communications options...

    Another thing to consider--It is actually quite difficult to "cost effectively grow/expand" an off grid power system... You may be able to add ~2x more batteries or solar panels--But beyond that, you start having to look at pretty much starting over (new battery bank with higher AH batteries, higher voltage AC inverter, new AC backup battery charger, a new/larger charge controller/MPPT charge controller, etc.).

    So, don't aim at one point while expecting the system to land elsewhere.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JaugJaug Registered Users Posts: 8
    Re: Undecided on Charge Controller

    Thanks Bill for showing me the right path to take. I have been eying the TriStar 60 Amp 12/24/48 Volt Pwm charge controller. As you mentioned I could go with something smaller than 60a. I believe the next step down for this model is a 40 or 45 amp.

    If I am not mistaken the Tristar has a 6 year warranty. I have also read some good reviews about their product. I would rather have one that can handle a few more amps so I could add one or two panels. I have not bought any battery's as of yet. First I want to plan everything out in the hope that I get it done right!

    Best Regards,
    Jim

    Once again thank-you very much for the advice....please let me know if you think or see where I might have other problems
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Undecided on Charge Controller

    Jim,

    It all gets back to loads to build out an "optimum" off grid/backup power system. The rules of thumbs I have used are based on being 100% off grid with generator (or grid) as your backup power for the loads I guessed at.

    Off grid power is never a "cheap solution" when you have grid available. It runs around $1 to $2+ per kWH when you run off of it 9+ months of the year. For backup power, it now is a capital cost/maintenance (i.e., battery replacement every 5-8 years or so, new electronics every 10+ years etc.) vs the cost of having "no power" or trying to keep a genset supplied with gasoline/propane/diesel/etc...

    No right or wrong answer--just more shades of gray.

    If you start with a "small system"--You are probably best off starting with components sized to operate the small system. If/when you want to go larger (if ever), you then can either sell/gift or even use the "old system" for a backup/extra cabin power system. And simply start fresh.

    About the only hardware that does "grow" pretty nicely as the system battery bank goes up in AH and voltage (12-48 volts), are the high end MPPT charge controllers. They can start out on a 12 volt and then run a 48 volt with a 4x larger array with just a minor configuration change/reboot on a new battery bank voltage.

    Their draw back, is the expense ($500-$600+) and the fact when running with a "Small" array , they are not that efficient (i.e., you have a lot of electronics, computer processing, switching elements) to run with a "small" array.

    It is tough--But between conservation and starting with a smaller system--You probably would be better off staying "small" and less expensive until you get the experience.

    On the other hand, a 3.3 kWH per day (100 kWH per month) capable system is not a bad compromise. It is large enough to run most reasonable loads--Including a refrigerator/well pump/washing machine (plus laptop computer, etc.). Just about the break point of "living a normal electric life" without grid.

    Off Grid PV power will (probably--always leave an out when predicting the future:roll:) never be cheaper than utility power (assuming that everything else is going up in price too--batteries/commodities/etc. in the near future)... About the only thing that may not is natural gas and possibly oil (assuming "Fracking" eventually hits public lands).

    But, if we get a collapse in infrastructure (such as in Urban Detroit where the city cannot $upport city $ervices with the abandonment of large parts of the city), then Solar Power many be a good solution for folks that live "out there" aways from available services.

    -Bill "hmm--why am I so "down" today--don't really feel different" B. :confused:

    Probably reading too much news on Cyprus.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JaugJaug Registered Users Posts: 8
    Re: Undecided on Charge Controller

    Yes Bill you hit the nail on the head....infrastructure!

    I lived in Germany for 25 years before returning to the States in 1998. I saw more power outages the first 6 months I was here than in my whole life. It is not only the grid that is out of date and in need of major renovation. The roads and bridges, lets not even talk about most of the water supply systems around the country. Speaking of the devil just last night the power was down for "several" hours. Used and inverter I have in a junk car that still runs. A rather wasteful way for back up!

    I also receive my water from my well which is around 150 feet deep.....would love to replace the 220v pump with a low volt or DC pump. When the grid is down = no running water. Those low voltage well pumps are very expensive. I will most likely use a 300 gal water container (which I have) keep it filled from the well (or with run off from the roof) and use a DC on demand pump on it. I would than set up one bathroom to use this. The water would not be portable.

    Best Regards,
    Jim
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