Parallel or Series MPPT 40 amp controller .

pyana1pyana1 Solar Expert Posts: 39 ✭✭
ive got two 250 watt sonali panels, stats read:

Voc 37.87v
isc 8.57a
vm 31.14v
im 8.10

with a morningstar mppt 40 amp controller
a go power 1500 pure inverter
and 4 trojan t105's .

do i mount my panels in series or parallel, i know series results to higher voltage and parallel does in amps.

in my particular case which is more efficient/beneficial?

i dont want a 48 volt system (series) so is parallel the cure for me?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Parallel or Series MPPT 40 amp controller .

    What Voltage system have you got?

    If it's 12 Volts, then paralleling the panels is best because that will be the least efficiency reduction of the controller from down-converting.

    If it's 24 Volts, then placing the panels in series is almost mandatory because the Vmp of 31 is pretty low for charging a 24 Volt system (chances are the Voltage would not be high enough once the panels warm up and further losses are incurred in wiring).

    Nota bene: 500 Watts of PV is not really enough to recharge four T105's in any configuration. It would be 32 Amps @ 12 Volts trying to recharge 450 Amp hours of battery; a 7% peak rate. Loads will reduce that further, making this a system operating "on the edge". It's easy to fall off that edge.
  • pyana1pyana1 Solar Expert Posts: 39 ✭✭
    Re: Parallel or Series MPPT 40 amp controller .

    the panels are 24 volts , i was told they could only be used with a mppt controller from the seller.

    i initially wanted a 1k of pv but was told to decrease the pv watts and purchase more battery then i wouldn't have to dig too deep in my battery bank thus not needing too much pv power?!?

    i will have one constant load : chest freezer about 50-80 watts

    nevertheless i wanted to keep everything 12 volts - battery, etc. but i'll settle for 24v if i have too.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Parallel or Series MPPT 40 amp controller .
    pyana1 wrote: »
    the panels are 24 volts , i was told they could only be used with a mppt controller from the seller.

    Not really important except for maximizing power. The issue is not the panel Voltage but what system Voltage you're trying to match it up with.
    i initially wanted a 1k of pv but was told to decrease the pv watts and purchase more battery then i wouldn't have to dig too deep in my battery bank thus not needing too much pv power?!?

    You were given bad advice. The old "lots of battery and a little PV" is not valid anymore as PV prices have dropped and battery prices have risen. The idea is to find a balance that will maximize the value of the batteries. Shallow discharge does not significantly increase lifespan over that with 25% DOD, but under-charging from insufficient PV does shorten battery life. The sun does not shine the same every day, so some margin for this must be allocated.
    i will have one constant load : chest freezer about 50-80 watts

    nevertheless i wanted to keep everything 12 volts - battery, etc. but i'll settle for 24v if i have too.

    The only reason to use 12 Volts is if you are stuck there owing to having already bought 12 Volt equipment or needing it (as in a mobile application). You would not be 'settling' for a 24 Volt system; they are more efficient than 12 Volts.

    Chest freezers don't run constantly. They will cycle on and off as any thermostatically controlled device will. It may use 80 Watts when on, but only be on 1/2 the time. This adds up to Watt hours and is what you need to know to size your battery bank. Four T105's would be sufficient to run most any refrigerator for a day.

    But you would definitely want more PV. If it were me I'd go for a 24 Volt system (all batteries in series) and double up the panels (two parallel strings of two in series) as you had originally planned.
  • pyana1pyana1 Solar Expert Posts: 39 ✭✭
    Re: Parallel or Series MPPT 40 amp controller .

    thanks Cariboocoot, what if i decided to go with 2 trojan t105s would i be able to power my freezer then?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Parallel or Series MPPT 40 amp controller .
    pyana1 wrote: »
    thanks Cariboocoot, what if i decided to go with 2 trojan t105s would i be able to power my freezer then?

    Possibly. The total available power drops in half of course. This means you get just about 1kW hour AC available and that at 50% DOD. Depending on exactly how many Watt hours the freezer plus whatever else is running uses and how good the sun is and how long you want the batteries to last ... there are many factors.

    The more towards minimum you go for a power system, the greater the chances of disappointment.
  • softdownsoftdown Solar Expert Posts: 2,682 ✭✭✭✭
    Re: Parallel or Series MPPT 40 amp controller .
    pyana1 wrote: »
    thanks Cariboocoot, what if i decided to go with 2 trojan t105s would i be able to power my freezer then?

    Sorry to butt in but my experience indicates that this battery bank would barely allow for substantial internet and tool usage. Plan on lots of generator usage during the winter.

    You can look at the numbers and think you will be fine. But there are losses, losses, losses everywhere when harnessing power from the sun. I know a lot of people with solar power. They are all amazed with how much solar it takes to produce somewhat comfortable living. Off gridders are quite often closer to camping than luxury.

    Just my .02, the mods here have forgotten more than I know.
    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
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