Hi , I am trying to design a solar / wind array to charge 3 "house" batteries of 150Ah (total 450 Ah). One of the questions I have, is that I have thought of 3*310 watt solar panels in one array, to feed an mppt controller then into the 12v batteries ( on a 12v system). I know the basic ohms theory , but it does not seem as simple as using the 310 wattage and divide by 12, to get 25.83 amps, therefore 77.5 amps (parallel configuration) fed to the mppt...or does it. ? I mean the panels i looked at were designed for a 12 volt system, yet ( and this is what i struggle with) the characteristics of one of the 310 panels is maxP (V) 31.77 volts and maxP (I) 9.13 amps. This seems to say, if i connect the panels in parallel, then the max current flow to mppt would be about 3*9.13 =about 27 amps. So what is correct, as this could make a difference in mppt required. Does it go with because the batteries required 12 v, then the current pulled down by the controller is 77.5 amps ??
Confuzzled with Amps input to and from Solar controller
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Hedges
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You said MPPT.
If you got PWM (Pulse width modulated) SCC, that is a switch which connects panels to battery, then opens if voltage gets too high. Then closes again, and cycle repeats. Current into battery would never exceed current coming from PV panels. (rating of one panel if all are in series, sum of ratings of panels if all are in parallel.)
MPPT provides Maximum Power Point Tracking of PV panel. It runs voltage of panel up and down, staying close to where V x I is maximum. That is done with a switching power supply, usually a "buck" configuration which only reduces voltage, can't increase. It uses an inductor for pulses of current and functions much like a transformer for AC. A variable transformer. It can take in 900W at 90V (10A) and put out 900W at 15V (60A), less some percentage loss due to inefficiency.
MPPT charge controllers have an absolute max voltage. Voc of panels must be adjusted for record cold temperature of you location, and added up for series connection. Never exceed max allowable Voc of MPPT under any conditions.
MPPT charge controllers have a max current they will deliver to batteries. They *should* limit their output to that, regardless of how much PV wattage is connected. They also *should* limit their temperature and power dissipation, even on a hot day.
MPPT might have a spec for maximum Isc of P array.
If you just add up PV watts and divide by 16V max battery or 10V min battery voltage, that's about the current that could be delivered on a cold, bright day.
If you got PWM (Pulse width modulated) SCC, that is a switch which connects panels to battery, then opens if voltage gets too high. Then closes again, and cycle repeats. Current into battery would never exceed current coming from PV panels. (rating of one panel if all are in series, sum of ratings of panels if all are in parallel.)
MPPT provides Maximum Power Point Tracking of PV panel. It runs voltage of panel up and down, staying close to where V x I is maximum. That is done with a switching power supply, usually a "buck" configuration which only reduces voltage, can't increase. It uses an inductor for pulses of current and functions much like a transformer for AC. A variable transformer. It can take in 900W at 90V (10A) and put out 900W at 15V (60A), less some percentage loss due to inefficiency.
MPPT charge controllers have an absolute max voltage. Voc of panels must be adjusted for record cold temperature of you location, and added up for series connection. Never exceed max allowable Voc of MPPT under any conditions.
MPPT charge controllers have a max current they will deliver to batteries. They *should* limit their output to that, regardless of how much PV wattage is connected. They also *should* limit their temperature and power dissipation, even on a hot day.
MPPT might have a spec for maximum Isc of P array.
If you just add up PV watts and divide by 16V max battery or 10V min battery voltage, that's about the current that could be delivered on a cold, bright day.
Ok thanks Hedges, so the mppt senses the battery voltage (12), and "if" the array was producing 930 watts, it would be supplying the 930/16 ( 58) amps max , or the 930/10 (93) amps minimum from mppt to batteries.. .. which makes me think a series array would be better to lower the current from array to 25 amps to the mppt. Although, the mppt can handle the sum voltages of array , in resolving that sum voltage then changing it to 12 volt O/P for batteries; the current would also be changed at output up to the 58 or 93 amps ? Is this logic correct , or that in the depths of the mppt it supplies 12v to the batts, but at the 25 amps input to mppt due to the array in series.
Hedges
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450 Ah (at 12V?) of batteries. What chemistry & type? What maximum and optimum charge current?
If FLA, possibly 0.2C or 90A charge is optimum. If AGM, possibly 0.1C or 45 Ah. If gel, definitely some low current. If lithium, probably fairly high.
But check documentation in any case.
Look at charge controller documentation to see efficiency and limits. It could be that efficiency is higher if input voltage is closer to output voltage (PV panels in parallel).
Wiring can be smaller gauge, IR losses are lower, no need to fuse parallel panels if in series. Voltage is high enough to be hazardous if in series.
If in parallel, can orient each different direction to reduce peak current and spread power production over more hours.
If FLA, possibly 0.2C or 90A charge is optimum. If AGM, possibly 0.1C or 45 Ah. If gel, definitely some low current. If lithium, probably fairly high.
But check documentation in any case.
Look at charge controller documentation to see efficiency and limits. It could be that efficiency is higher if input voltage is closer to output voltage (PV panels in parallel).
Wiring can be smaller gauge, IR losses are lower, no need to fuse parallel panels if in series. Voltage is high enough to be hazardous if in series.
If in parallel, can orient each different direction to reduce peak current and spread power production over more hours.
I was looking at the possibility of 3*150 LifePO4's such as Victron, at 12v and wired in parallel. I did see somewhere that the charge current should be about 30% of Ah, just trying to get the limitations of components. I have a secondary conundrum, in adding another solar/wind controller into the mix; both that additional controller with the original. Read you can do it , just should try and keep max current of both to the 30%.
My 2nd array would be through it's own controller, with combo of wind gen (max 480 watts about 35 amps ) combined with about 200 watts of solar . But i need to investigate the combination of the 2 systems being wired onto the battery bank together.
My 2nd array would be through it's own controller, with combo of wind gen (max 480 watts about 35 amps ) combined with about 200 watts of solar . But i need to investigate the combination of the 2 systems being wired onto the battery bank together.
Hedges
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Usually wind won't produce anything (except maybe if you're on a boat), and wind/sun are usually complementary.
Ideally you have a system that considers all charge sources and loads, regulating battery to target charge rate.
With lithium you do get a wider range of acceptable charge current.
So you're going to have 5000 Wh of battery, 480W peak of wind, 200W peak of PV. Well under 1500W 30% max allowed charge rate.
Ideally you have a system that considers all charge sources and loads, regulating battery to target charge rate.
With lithium you do get a wider range of acceptable charge current.
So you're going to have 5000 Wh of battery, 480W peak of wind, 200W peak of PV. Well under 1500W 30% max allowed charge rate.
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