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Connect my solar panel for maxium output?

MinhProUS

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Jun 19, 2021
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Recently I am learning about 12v/24v/48v system, the more I learn the more I got confused, please help me out

My current off-grid system using inside my house

Solar panel 3 x 12v 200w
Renogy Charger controler 40A MPPT
Battery 300Ah Lithium Ampere Time
Inverter 12v 2000w Xantrex

My Question is:
1. Will I get more power out of my solar panels by connecting them in series to get 24v (i will save the extra pannel just in case something will happen) instead of parallel 3 of them in 12v system like I am using. Can you please explain?

2. I am currently getting around 32A (16-18v MPPT) when it is full sun. How long will it take to charge an empty 300Ah battery and expense of 2kw of household use, using my current solar system? Should I buy more panels or batteries?

3. Will the Renogy Charge controller lower the voltage from 24v solar panel to 12v to charge my battery (the manual said auto-detection of 12/24v system)
 
Assuming THIS is your charge controller ...

Connect all three solar panels in series to get 36 volts. The above controller can accept solar voltage up to 100 volts. The controller will automatically detect your system (battery voltage) and charge accordingly. Make sure you have set the controller for the correct battery type. Time to charge will depend upon sun conditions.
 
Assuming THIS is your charge controller ...

Connect all three solar panels in series to get 36 volts. The above controller can accept solar voltage up to 100 volts. The controller will automatically detect your system (battery voltage) and charge accordingly. Make sure you have set the controller for the correct battery type. Time to charge will depend upon sun conditions.
I think mine is a little older version.
https://www.renogy.com/rover-elite-40a-mppt-solar-charge-controller/

Would you please explain the reason to put them in series of 36v. Thank you very much for your help?
 
I am setting Li - 12v system - 14.0 voltage on the charge controller.
Should I go higher to 14.4 -14.6v , or keep it at 14.0v? Which one will be better for Lithium battery life?
 
By running a higher voltage (36 instead of 12) you can use smaller wire to connect the panels to the controller. You will also have less voltage loss. In other words, it is a more efficient way to do it.
 
The unstated part of the series question is that the 24V you asked about is that to use all three panels either 3 parallel or 3 series are your only options.
One more identical panel and 24V is doable, and in some circumstances 2S2P might offer advantages over a single 3S string
 
Wire them in series.

Charge voltages: 13.8 or 14V bulk, 13.2V float.
 
Your '12v' panels are actually around 22 volts open circuit and 18 volts at maximum power.
Will I get more power out of my solar panels by connecting them in series to get 24v
If you connect in series or parallel the solar panel power will be the same, 600 watts. The MPPT controller takes whatever power exists on the input and converts to a voltage suitable for the battery. In series you have, at maximum power, ( 18+18+18 ) volts and 11 amps into the controller. In parallel you have 18 volts and (11 +11+11) amps into the controller.

In practice the series connected panels will 'switch on' the MPPT controller slightly earlier in the day and off later is the day. However the additional power collected is low.
currently getting around 32A (16-18v MPPT) when it is full sun. How long will it take to charge an empty 300Ah battery and expense of 2kw of household use
Depending where you live, angle and direction of panels and time of year, the solar yield will vary. There are various on line calculators that allow you to calculate yield.
Assuming you get 600 watts for 6 effective sun hours, 3600 watts per day,
If the consumers are 2000 watts per day the surplus is 1600 watts or 120Ah at 13.2 volts per day.

You need to investigate the typical solar yield for your setup in the worst case time of year/weather conditions and work from there.

. Will the Renogy Charge controller lower the voltage from 24v solar panel to 12v to charge my battery
As I said, the solor panel input could be 54v is in series and 18 volts in parallel for so called '12v panels'. The MPPT controller is a power converter. For information a '24v panel' will have an open circuit voltage of around 42 volts and a maximum power voltage of around 37 volts
the manual said auto-detection of 12/24v system
This refers to the battery system not the solar input. When the battery is connected it auto selects the 12 or 24 volt charging profile.
A typical charge controller rated at 40 amps will deliver a maximum of 40 amps into a 12v battery or a 24v battery.
On the solar input side it will have a maximum current input of 40 amps and a voltage input maximum of 22 volts and higher, at a guess your controller is rated at 40 amps and 100 volts.

Mike
 
or keep it at 14.0v? Which one will be better for Lithium battery life?
Lower is better, but below 13.8 volts charge time is longer, 14v is a good compromise, stop charge as soon as you reach 14v, no or very short absorption (constant voltage) period.
Float below 13.4 volts unless you require to power loads during the day with surplus solar, then set to 13.5 or 13.6 volts.

Mike
 
May not make that much of a difference in output. With the parallel panels, you will need thicker wires, and also may exceed the 30 amp rating of 10 gauge and MC4 cables, so you may need to go with thicker wire if you choose that. The expense of a 40' run of 6 AWG wire compared to 10 AWG wire is not all that much. If you have 1000' of wire it is. With parallel you really need to look at voltage loss with runs after the panels are combined.

I have portable panels that I set up four in parallel in case one is shaded. On a cloudless day with the panels pointed to the south and angled to the sun, I see between 90% and 104% of the panels rating. If I shade the panel by putting my hand over the panel, I lose 80% of the output of a single panel. So I would produce 19 amps total with one panel shaded instead of 24.

If shading is a factor, you could get more output from the panels in parallel. I'm told if I have these panels in series and one gets shaded, that the bypass diodes kick in. I have not set them up in series to test this to see what it means in real numbers, but I have a feeling that the output would be similar to the other example.

I am doing a 24 volt battery upgrade where my four panels will no longer be able to be in parallel because they will not produce enough votlage to charge the batteries, and I will put them 2 in series to get the voltage, and then I will test.
 
If you connect in series or parallel the solar panel power will be the same, 600 watts. The MPPT controller takes whatever power exists on the input and converts to a voltage suitable for the battery. In series you have, at maximum power, ( 18+18+18 ) volts and 11 amps into the controller. In parallel you have 18 volts and (11 +11+11) amps into the controller.
In practice the series connected panels will 'switch on' the MPPT controller slightly earlier in the day and off later is the day. However the additional power collected is low.
I agree. I put them in series around 1930 and I saw an increase in the amp on charge controller from 0 Amp to 1.5 Amp, and right now I am seeing around 35 Amp instead of the normal 33 Amp,

The reason I had them in parallel because I bought the solar set from Costco that includes the PWM charge controller

wer is better, but below 13.8 volts charge time is longer, 14v is a good compromise, stop charge as soon as you reach 14v, no or very short absorption (constant voltage) period.
Float below 13.4 volts unless you require to power loads during the day with surplus solar, then set to 13.5 or 13.6 volts.
My charger controller doesn't have the option to change the float voltage, I think it does automatically.

If shading is a factor, you could get more output from the panels in parallel. I'm told if I have these panels in series and one gets shaded, that the bypass diodes kick in. I have not set them up in series to test this to see what it means in real numbers, but I have a feeling that the output would be similar to the other example.
I will need to test the effect of shading later. I don't really know whether my solar panels have the bypass diodes or not.

Thank you all for your input. I really appreciate you all.
 
I don't really know whether my solar panels have the bypass diodes or not.
Nearly all panels on the market have bypass diodes built into the junction box.

from the link above,

The junction box is generally located on the back of the panel. It contains bypass diodes to help with power loss due to shading. Also it serves as a connection and a holder for the panel wires.

Mike
 
My charger controller doesn't have the option to change the float voltage,
I can’t remember now but I’m pretty sure the pwm from windyNation (P30L) gives you that control. For $35/$40 I’d buy one: still 30A but I ran mine for several years snd I was very happy with it. Running an mppt controller now but the P30L did pretty good for me.
There’s probably others that will work as well or better I just don’t know what they are.
 
You only have rated 600W of solar, depending on where you are, you will only get 4-6 effective hours of max sun. So 2.4 - 3.6kWh of energy per day. I am assuming your 300Ah battery is 12V, so you have around 3.5kWh of battery. You panels would be barely able to charge your battery if you use drain most of it in one day.

I think you should wire all 3 of them in series if you controller can handle the voltage. Series wiring will add the voltage, allowing your panels to start working earlier and end later. The one disadvantage of series is that shading on one panel affects the whole chain badly, so try to put in a spot where no panel will be shaded. If that is unavoidable, then parallel would work better as partial shading doesn't impact the whole chain as much. But you'll get a bit less efficiency due to more wire loss and you may need to use thicker wire.
 
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