should I connect my panels in series or parallel? - Fiberglass RV
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Old 08-18-2020, 08:07 AM   #1
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Name: Dominic
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should I connect my panels in series or parallel?

Hi I'm about to add solar to my bigfoot I bought the following components:
-2x170 watt bougerv solar panels
-2x20 foot 10 awg cables

-40amp mppt renogy charge controller
-a 100 ah lithium battery


I'm wondering if I should connect them in series or parallel. From what I understand I would have an advantage to connecting them in parallel, in that if one panel is shaded it would not affect the other panel. I'm wondering if there is an advantage to connecting in series? Also if I go with parallel I'll need to order a y connector so, I would prefer going with a series connection I think.



any thoughts/advise appreiciated
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Old 08-18-2020, 08:24 AM   #2
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When you connect panels in parallel, you stack the amps so you would add the maximum amperage of each panel to find the total maximum amps produced. Your charge controller must be able to handle the maximum amperage input from the panels.

When you connect panels serially, you stack the volts so you would add the maximum voltage each panel can produce to find the total maximum voltage produced. Your charge controller must be able to handle the maximum voltage input from the panels.

You will need to read the manual for your controller to see what the maximum input parameters for amps and volts are. If it does appear that the charge controller can handle the voltage of the panels in series, verify the output of the controller can be set to whatever voltage your batteries need. This can be a single 12 volt battery, two 6 volt batteries in series to take 12 volts or two 12 volt batteries in series to take 24 volts.
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Old 08-18-2020, 08:26 AM   #3
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If the charge controller can handle both series and parallell (99% sure it does), then I would have an advantage to connecting in parallel right?
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Old 08-18-2020, 08:29 AM   #4
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Short Answer: Parallel.

Long answer... Alex hit on most of it so no need to repeat. Panels in series are mostly used for larger installations where higher voltage has some advantages (longer wire runs, etc). But you do need controllers designed for that, and in many cases these larger scale installations use multiple smaller controllers combined with larger ones. Those are actually inverters that change the DC to AC, often close to the panels. This works better for large scale setups.

In your case, also consider fuses on the panels.. generally fuses are not needed in a single panel setup but with more than one fuses are often recommended.
https://www.renogy.com/blog/how-to-f...-solar-system/
https://www.windynation.com/jzv/inf/...are%20required.
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Old 08-18-2020, 08:36 AM   #5
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I am no expert, but from what I have read it can be better to use serial input from the panels and let the controller output the 12 volts to the battery. Part of the reason is there is less voltage drop in the wiring from the panels to the charge controller due to lower amperage. Hopefully someone more knowledgeable than I will pipe up.
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Old 08-18-2020, 08:38 AM   #6
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The most often reason for wiring panels in series it to limit current, allowing smaller wires. This is not as important for our smaller trailers because the wire runs are usually fairly short.

In addition to the shading problem presented by serial wired panels, another advantage of wiring your panels in parallel is the ability to add a portable panel to the system. Many carry both roof mounted panels & a portable to add when parked in heavy shade or mid winter camping when the sun angle is low, limiting output from the roof panels. As long as the voltages are close, a portable panel can be added in parallel. If the portable panel has a built in controller, I'd bypass it and connect it to the input of the trailer's controller.

Again, as Alex mentioned, your controller must be rated for the total current & voltages produced, however the actual amperage produced by panels, particularly non tilted rooftop panels, will be quite a bit less than their ratings.
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Old 08-18-2020, 09:06 AM   #7
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It depends on if you have an MPPT or a PWM controller. My three panels work at a lower light level with the MPPT in series. If the panels have bypass diodes and one panel is shaded it will still produce power. The MPPT, in my opinion, runs the panels at the peak power point and converts that to the voltage to charge the battery(ies).
The MPPT is worth the money to me as my system starts charging earlier and keep charging later and at lower light levels.
Sometimes the three panels in series barely generate enough voltage and current to charge, but the parallel would have been out of business completely.
Your mileage may vary.
This means that since permanently mounted panels are most often not optimized except (perhaps) for briefly at noon. This is why I have 300 watts mounted on my roof to make up for the inefficiencies of mounting and location.
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Old 08-18-2020, 09:58 AM   #8
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It's the voltage...

You have no choice, the voltage the panels produce must match the voltage of your battery bank. If you have 12volt panels and one or a set of 12v batteries wired in parallel (all + connected, all - connected) you must wire your panels in parallel to output 12volts.

If you have a 24 volt battery bank, (Plus, then minus to plus, then minus) and two 12volt panels, you must wire the panels in series to produce 24volt. Systems using 24volts (or 48) are more efficient due to lower heat losses from high currents in the cables.
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Old 08-18-2020, 10:02 AM   #9
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I thought that the MPPT controller would do the proper conversion
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Old 08-18-2020, 10:06 AM   #10
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Quote:
Originally Posted by wallnut1234 View Post
I thought that the MPPT controller would do the proper conversion
It does as long as the output voltage is programmed to match the voltage of your battery bank.
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Old 08-18-2020, 10:09 AM   #11
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Originally Posted by wallnut1234 View Post
I thought that the MPPT controller would do the proper conversion
It does. Series or parallel is not determined by battery voltage.
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Old 08-18-2020, 10:38 AM   #12
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Originally Posted by brucewarren View Post
You have no choice, the voltage the panels produce must match the voltage of your battery bank. If you have 12volt panels and one or a set of 12v batteries wired in parallel (all + connected, all - connected) you must wire your panels in parallel to output 12volts.
...
Wrong.

A typical 100 watt solar panel will have a Open Circuit Voltage (Voc) of about 22 VDC. In use, usually actual voltage is closer to 17 - 19 or so. The controller (PWM or MMPT) converts that to the proper charging voltage and should adjust the output voltage in the different stages of charging. It all depends on what solar controller is used.

Now if you wire two of those panels in series it will be a Open Circuit Voltage (Voc) of 44 VDC to the controller. If the controller is speced for that then it will be happy with the two panels in series and will still output the nominal voltage for the single battery (or as programmed). For a single regular 12 volt battery that output voltage is between 13 and 15 volts (depending on the charge profile).

So while your statement is wrong, your conclusion is right but for different reasons. In this application wire in parallel .

Learn more here.
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Old 08-18-2020, 10:46 AM   #13
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The MPPT or at least mine detects the battery voltage and controls accordingly.
In my case the solar panels can build up to over 60 volts for the most efficient production of power and the MPPT inverter transforms that to the proper charging voltage for the state of the batteries.
If you look at the specifications of the panels you will see that the voltage and currents are not usually at the proper level for battery charging, thus the controller.
In the case of the MPPT the load on the panels is adjusted to to the point where the array is producing the maximum power. Often the controller is putting out more current (amps) than is being produced by the solar panels because they are producing power at 60 volts total.
For example if the array is producing 1 amp at 60 volts that is 60 watts. That 60 watts is transformed at close to 100% efficiency to charging voltage lets just say 13 volts so I=P/E = 60/13 = 4.61 amps.
Of course paralleled panels will produce more current (1 amp X3=3), but (and this is a big but) they will not be operating at their most efficient power point when at charging voltage. Often the MPPT will produce as much as 20 - 30 % more power.
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Old 08-18-2020, 11:04 AM   #14
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Quote:
Originally Posted by redbarron55 View Post
The MPPT or at least mine detects the battery voltage and controls accordingly.
In my case the solar panels can build up to over 60 volts for the most efficient production of power and the MPPT inverter transforms that to the proper charging voltage for the state of the batteries.
If you look at the specifications of the panels you will see that the voltage and currents are not usually at the proper level for battery charging, thus the controller.
In the case of the MPPT the load on the panels is adjusted to to the point where the array is producing the maximum power. Often the controller is putting out more current (amps) than is being produced by the solar panels because they are producing power at 60 volts total.
For example if the array is producing 1 amp at 60 volts that is 60 watts. That 60 watts is transformed at close to 100% efficiency to charging voltage lets just say 13 volts so I=P/E = 60/13 = 4.61 amps.
Of course paralleled panels will produce more current, but (and this is a big but) they will not be operating at their most efficient power point when at charging voltage. Often the MPPT will produce as much as 20 - 30 % more power.
But, and this is another big but - if you want to add a portable panel to the input of the controller, the higher series voltage will not match the portable panel.

Both methods will work, and there are advantages & disadvantages to each. Depending on your situation, choose the wiring system that works best for you.
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Old 08-18-2020, 11:24 AM   #15
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Following discussion.
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Old 08-18-2020, 11:38 AM   #16
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You picked a Lithium battery which works well with a MPPT controller. Lead acid batteries will only charge up to about 75-80% before the controller goes into constant voltage mode and your solar controller will be no better than a PWM controller. Lithium will accept all the power you can supply up to around 95% of full charge. Secondly, as mentioned earlier, a series connection can generate a high enough voltage to provide some charge current to the batteries in low light conditions. For example if the panel voltage drops to 14 volts, nothing will go to the batteries, but a series connection will be generating 28 volts which is something the MPPT controller can work with and provide some current.

If most of your camping will be in open skies then a series connection will have some advantages. If you tend to camp in partial shading then parallel would be better.

The Y connectors, you will need two of them, are not a lot of money compared to the rest of the equipment, so I would recommend purchasing them and do a little testing on your own. Try hooking them in series and see what you get. Try blocking one panel, see what happens. Reconnect them in parallel and do some testing. It is trivial to change from a parallel to serial connect. Have some fun with it.

If you are planning on adding a portable panel some day you can either purchase one with a built in lithium compatible controller or purchase a cheap PWM controller that works with lithium technology. Just connect it directly to the battery.
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Old 08-18-2020, 01:38 PM   #17
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No need for a charge controller

Quote:
Originally Posted by wallnut1234 View Post
I thought that the MPPT controller would do the proper conversion
My four panels are 24volt units. Open circuit they put out 30 volts in full sun. All wired in parallel. No charge controller. Wired directly to four 6volt golf cart batteries wired in series, two banks. Connected directly to the battery bank is a 2,000 watt inverter for 120vac. Been working great for a year. Prior to that I had a charge controller and the batteries never really got charged right. The charge controller is expensive and just another failure point.

The folks who sell solar panels love to max out the things you need to buy. If you are doing a house with a tie-in to the electric grid, then you need all that stuff. But not for an RV.
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Old 08-18-2020, 02:17 PM   #18
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Originally Posted by brucewarren View Post
..
The folks who sell solar panels love to max out the things you need to buy. ....
Assuming for a moment that is true, why not check with the battery manufacturer about charging with unregulated panels....
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Old 08-18-2020, 02:21 PM   #19
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Originally Posted by brucewarren View Post
My four panels are 24volt units. Open circuit they put out 30 volts in full sun. All wired in parallel. No charge controller. Wired directly to four 6volt golf cart batteries wired in series, two banks. Connected directly to the battery bank is a 2,000 watt inverter for 120vac. Been working great for a year. Prior to that I had a charge controller and the batteries never really got charged right. The charge controller is expensive and just another failure point.

The folks who sell solar panels love to max out the things you need to buy. If you are doing a house with a tie-in to the electric grid, then you need all that stuff. But not for an RV.
walnut1234, you have a LFP battery not a lead acid battery. If you hook your system up without a controller you will overvoltage the batteries and it will cost you lots of money. Applying an over voltage to lead acid batteries will cause electrolysis which produces hydrogen gas, (which is somewhat explosive) ultimately reducing battery life. You are going in the correct direction.
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Old 08-18-2020, 03:28 PM   #20
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walnut1234, you have a LFP battery not a lead acid battery. If you hook your system up without a controller you will overvoltage the batteries and it will cost you lots of money. Applying an over voltage to lead acid batteries will cause electrolysis which produces hydrogen gas, (which is somewhat explosive) ultimately reducing battery life. You are going in the correct direction.

yes I have a MPPT controller so I will be using it for sure. Like it was suggested I will be experimenting with parallel and series setup to compare results. Thanks for the heads up though
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