MPPT charge controllers and their abilities

CALLDCALLD Solar Expert Posts: 230 ✭✭
Ok, so I'm finally looking at doing things properly now and need to know everything there is to know about MPPT.

The final setup is going to be 6 x 300 watt modules, each producing 36.6v vmp and 45v voc.

What is the best configuration with an MPPT controller charging a 24v battery? Assuming PVs are all facing exactly the same direction with none of them having any shading problems during the day can I hook them all up series? Are there MPPT controllers that will happily convert 220v (or more depending on conditions) into the required battery voltage? Does input voltage affect the performance or efficiency of the controller? If I get a 100 amp MPPT controller will it be adequate? As for batteries I'm up for suggestions but am currently looking at keeping my 260Ah VRLA set because I'm planning to use a lot of the power during the day so only a portion will be going towards charging in general. The additional PV is also supposed to help with keeping things going on very cloudy days and to help alleviate under charging in winter.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT charge controllers and their abilities

    No, you definitely do not want them all in series. There are not any charge controllers that can handle that, including the Classic 250, as the Voc would be way over the limit. Nor is there any such thing as a 100 Amp charge controller.

    The panels you describe can be used all in parallel on a 24 Volt system, or as three parallel strings of two in series. Raise the array Voltage too much above system and the controller efficiency goes down. As a rule you don't go for high array Voltage unless it is needed to overcome loss in wiring between the array and controller.

    Six 300 Watt panels would be 1800 Watts. On a 24 Volt system the current would be around 58 Amps, which means any 60 or 80 Amp MPPT controller would work. That much current is too high for 260 Amp hours of battery. This presents a problem in that even with loads the batteries may be subjected to excess current under certain conditions. If you had 390 Amp hours you could do this. Otherwise it would be a good idea to limit the current output or at least the current to the battery, which would require something like the Outback FNDC.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: MPPT charge controllers and their abilities
    CALLD wrote: »
    The final setup is going to be 6 x 300 watt modules, each producing 36.6v vmp and 45v voc.

    What is the best configuration with an MPPT controller charging a 24v battery?

    OK, so now that you have chosen a PV panel....To use a single panel: the answer to this question depends on your battery, in general, an AGM should be able to be fully charged with that, DEPENDING on the makers charge parameters... An FLA battery might be chargeable but and depending again you need to know the absorb voltage needed... I doubt you will be able to EQ some of the higher EQ voltage needing brands.

    I am betting on a 2-in-series configuration if everything is close together.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT charge controllers and their abilities

    Forgot to provide this link to the basics of MPPT array configuration: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
  • CALLDCALLD Solar Expert Posts: 230 ✭✭
    Re: MPPT charge controllers and their abilities

    Hi coot, thanks for the advice. It was your advice on minimum charging current in previous threads that has me leaning towards a much larger array for my batteries. I was hoping there was a charge controller out there that could step down a much higher array voltage so that I wouldn't need to purchase much thicker cabling as well for the setup. But if it has to be done ill do it.
    Microcare has a 100 amp MPPT controller.
    The reason I would like one that size is I know I will get surges of over 70 amps in summer that can last for several minutes and would like to have a good safety margin.
    My batteries say they can handle a maximum charging current of 78amps.
    The need for a larger array is that there will be many days where 10 amps is all I get at most. There will also be days where I will get 60 or 70 amps but only for an hour or two & have to make do with that. As far as boost chargers for use with the grid or generator goes it is actually cost effective to get additional PV instead as these chargers are very expensive here.
    Why pay for the power when you can get it for free from the sun?
    In winter the array would likely be peaking at 35 to 40 amps with MPPT boosting it by 10 to 25 %.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT charge controllers and their abilities
    CALLD wrote: »
    Microcare has a 100 amp MPPT controller.

    Never heard of it. What's more, knowing how hard it is to handle such current levels I wouldn't trust it.
    The reason I would like one that size is I know I will get surges of over 70 amps in summer that can last for several minutes and would like to have a good safety margin.

    How do you come to the conclusion you will get 70 Amp surges? An array puts out according to its size, insolation, and load. Short the output in full sun on a cold day and you get Isc, which is only slightly above Imp. Even with an ultra-large array the current will be limited to the max the charge controller can handle, providing its a good controller. You are predicting an impossible possibility.
    My batteries say they can handle a maximum charging current of 78amps.
    The need for a larger array is that there will be many days where 10 amps is all I get at most. There will also be days where I will get 60 or 70 amps but only for an hour or two & have to make do with that. As far as boost chargers for use with the grid or generator goes it is actually cost effective to get additional PV instead as these chargers are very expensive here.
    Why pay for the power when you can get it for free from the sun?
    In winter the array would likely be peaking at 35 to 40 amps with MPPT boosting it by 10 to 25 %.

    The problem with upping the array size for better charging on cloudy days is that it only works to a limited extent. You can't predict the insolation drop, but you can understand that PV is current-based and when the light falls off so does the current, no matter how many panels you have. It gets ridiculous very quickly, with the Imp falling rapidly from only slight loss of sun. The output is not at all linear. Trying to size an array for days when 1/10 power is all you can get is a waste of panel. So when it comes to expense, the gen & charger is cheaper and certainly more reliable for dark day charging.

    Solar power is far from free, and running the array size up to where it can provide charging in low light conditions makes it incredibly expensive because those panels will be doing nothing when the sun shine; a waste of capital.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    Re: MPPT charge controllers and their abilities

    I've seen over 60amps go into my AGM's and they have a printed limit of 72amps, but that is per battery. At least that is what I have been told. I dump over 120amp into my bank almost daily during Bulk charging. Not sure about splitting up amperage inputs on FLA's.
Sign In or Register to comment.