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Old 01-30-2020, 01:37 PM   #1
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Solar test

I'm currently installing 2 200 watt panels, in series on my Jayco Seneca. I decided to test the efficiency of the panels in varying degrees of sunlight. I found that with the sun at an angle just above the horizon or about 5 degrees angle to the panels, I'm reading about 45.6 volts. That was surprising because at 90 degrees or a straight up angle to the panels, the voltage reads 49.8 volts. Not much of a loss at severe angles. It seems to me that it is pretty useless to have hinged panels that you have to climb up on the roof to adjust in order to get maximum efficiency. Is it worth a difference of only 4.2 volts to go to the effort? Any thoughts?
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Old 01-30-2020, 03:24 PM   #2
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With solar panels it is not the volts that count but the current they can produce. If you put a load on it the voltage will drop off pretty quickly but that is not a problem. I think my panels put out in the high 20s with no load. As long as it is above typical battery charging voltage it is good. The controller will knock it down to high 13 volts or low 14 volts for the battery.

Does your controller show amperage output? That is what you should be looking at. Watch the display while you add some 12 volt loads. If you have an inverter fire it up with some 120v item running as it will put a heavy load on your battery which the solar will try to replenish.

I have 2 100 watt panels but have never really tested how much they can put out because I have to crawl under my slide out to view the controller. I have been wanting to do it just never have gotten around to it. I thrive on procrastination. I do know I have seen it putting out 8 amps but that is not with a major load.
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Old 01-30-2020, 03:26 PM   #3
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I just reread your post. Why are you connecting them in series? They should be in parallel. In series the voltage will go up but the current will not. Current is what you need here not voltage. I assume you are working with 12 volt batteries and not 24 volts or above.
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Old 01-30-2020, 03:40 PM   #4
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You are correct about the current but with the panels in series, you will maintain the proper current if one of the panels is in the shade. It is correct either way as long as you have an MPPT controller with the panels in series. The voltage or the amps will not change just after the panels with a load. The controller will adjust as per the load. It operates from the incoming voltage. So it still wont be of much advantage to tilt the panels. In other words, I measured the voltage right from the panels before connecting them to the controller. That was the purpose of the test.

The amps were also unchanged with the sun at lower angles.



Thanks for your info on the operation of the charge controller. I will check the difference in current with a load on my next test.
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Old 01-30-2020, 08:36 PM   #5
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You are correct about the current but with the panels in series, you will maintain the proper current if one of the panels is in the shade. It is correct either way as long as you have an MPPT controller with the panels in series. The voltage or the amps will not change just after the panels with a load. The controller will adjust as per the load. It operates from the incoming voltage. So it still wont be of much advantage to tilt the panels. In other words, I measured the voltage right from the panels before connecting them to the controller. That was the purpose of the test.

The amps were also unchanged with the sun at lower angles.



Thanks for your info on the operation of the charge controller. I will check the difference in current with a load on my next test.
That's surprising that your amps generated by the panels were not very different either. What was the current output for the panels for each sun position? And, what was the mppt controller pushing out to you battery, the most important number. Unless your batteries were mostly full and the first reading you took was low sun in the morning then again when it was straight up, it's possible your batteries were full and the controller tapered off to float charge.
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Old 01-30-2020, 10:23 PM   #6
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At this point I've only checked the current at the panels before connecting to the controller. I'll be checking that tomorrow. The batteries are fully charged but I will deplete them a bit to see how the current changes.
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Old 01-30-2020, 10:26 PM   #7
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Amps were 7 at the low angle and 8 at the straight up angle.
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Old 01-31-2020, 10:06 PM   #8
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Amps were 7 at the low angle and 8 at the straight up angle.
For this time of year, 7A at a low angled sun for 200w of panels seems a bit high. What are they each rated at, about 5A each panel?
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Old 01-31-2020, 10:24 PM   #9
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Rated at 9.5o amps
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Old 01-31-2020, 10:35 PM   #10
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I just looked at the specs for the Windy Nation panels I installed. I may have been expecting more from them than they can produce.

I have 2-100 watt panels. Well, at say 12.6 volts 100 watts would basically equal about 8 amps. So I was hoping my 2 panels would give me 16 amps under full sun.

Well, according to the manufacturer, max power current is 5.75 amps. This means my wishful thinking of 16 amps for the two panels only equates to 11.5 amps. This is probably at the equator when the earth is its closest to the sun and directly overhead.

So I guess I will just be happy with some free energy from the sun. Maybe I should add a third panel.
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Old 01-31-2020, 10:45 PM   #11
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I've read that, technically you should double the current but voltage is the same with parallel panels. Valtage and amps are additive with panels wired in series. I'm sure they are somewhat over rated or as you say, at the equator mid summer. Actually, in series the curent stays the same, not doubled.
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Old 02-01-2020, 12:00 AM   #12
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I read the install instructions for my panels and you are suppose to wire them in parallel unless you are setting up for a 24 volt system.

I don't believe the panels when connected in series would be additive in current. Voltage yes but current, probably not.

Take 2 batteries. When connected in series the voltage doubles but the current is only the amount of one battery. I was always taught that voltage in series is additive and current in parallel is additive. Of course this is dusting off my old electronics training.

If the current was additive in series for solar, the instructions would have us install everything in series.

Just my opinion. Guess I should ask my son who is a solar installer electrician for Tesla.
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Old 02-01-2020, 05:54 AM   #13
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Originally Posted by dcs500 View Post
I'm currently installing 2 200 watt panels, in series on my Jayco Seneca. I decided to test the efficiency of the panels in varying degrees of sunlight. I found that with the sun at an angle just above the horizon or about 5 degrees angle to the panels, I'm reading about 45.6 volts. That was surprising because at 90 degrees or a straight up angle to the panels, the voltage reads 49.8 volts. Not much of a loss at severe angles. It seems to me that it is pretty useless to have hinged panels that you have to climb up on the roof to adjust in order to get maximum efficiency. Is it worth a difference of only 4.2 volts to go to the effort? Any thoughts?
I am curious, you installed 2,200 watts on your Seneca? I am struggling to get 1,200 watts. What is your model? I have a 2019 37RB. I have 232 sq ft of roof, minus the ac units, fans, skylight, tv antenna and my dish. Leaving me just under 200 sq ft. Can you share your panel size and maybe a diagram/photo of your layout? I'd love to put more than the 1,200.
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Old 02-01-2020, 09:07 AM   #14
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I installed 2 panels of 200 watts each. 200 not 2200.
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Old 02-01-2020, 09:39 AM   #15
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Renogy recommends that if the distance of the panels to the controller is more than 25 ft, you will lose voltage and to then wire panels in series. Others recommend 4 gauge wiring if the distance is 50 ft or more. In series, you can use a smaller gauge wire because the current is not additive. My motorhome has 6 gauge wire from the roof to the controller and is about 50 ft in total. That's why I went with series. I have 4 batteries and a Renogy controller which, upon demand can boost the current. For instance, the MPPT type controller can have 8 amps going into it and send 10 amps to the battery bank. So if I wired the panels in parallel, I would worry a bit about the wire gauge size and losing voltage. Let me know if this makes sense to you. I appreciate your expertise in electronics. Let me know what your son thinks. Thank you.
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Old 02-02-2020, 10:23 AM   #16
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I'm adding a second 100 watt panel and will go in parallel. Shading is more of a concern up here. That will impact the current produced, for me, more than wire gauge or length.


Going beyond 200 watts is a ways off, but right now, my head is thinking if I add a 3rd and 4th panel, then I'll parallel those together in a "new group" and go serial between two groups of 200 watts.
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Old 02-02-2020, 10:33 AM   #17
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Going both ways with series and parallel is the best of both worlds from what others have indicated. If I go with 2 more panels, I will do them in parallel but hopefully won't lose too much in current because of the length and gauge of the wiring. I just need to learn from others who have done this with similar conditions. It is recommended to use an MPPT controller if you go in series and will be compatible with the combination. Have fun.
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Old 02-02-2020, 03:35 PM   #18
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Series or parallel, that is the question. Simple answer - contact the manufacturer and see what they recommend. I followed my install instructions and went parallel. For mine, series was only used when going to a 24 volt set up.
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Old 02-08-2020, 03:23 PM   #19
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Series or Parallel?

Series is fine so long as you don't exceed the input voltage for the charge controller.

Series keeps current down if you are wired with relatively light gauge wire.

Rough estimates.
100 watts can generate about 7.5 amps of current (Windy Nation spec.)
400 watts can generate about 30 amps.
30 amps is a ton of amps and requires major wire gauge.
But run all 400 watts in series and....
Again, Windy Nation spec for a 100 watt panel, a 100 watt panel can put out as much as 18 volts.
4 of these in series can pump out all of 72 volts.
As far as wire goes, 72 volts is nothing.
Most charge controllers can handle 72 volts in to make 12 volts out.
72 volts at about 7.5 amps allows the use of standard #12 or #10 AWG wire to connect the panels to the charge controller. Convenient.

Of course, a pair of 200 watt panels in parallel would put out.... about 30 amps.
One of these should put out 15 amps.
So in series, 2 x 200 watt panels will put out roughly 72 volts at 15 amps. #12 or #10 wire can handle this with little loss.

This enables connecting to the charge controller with reasonably sized wire. But if you're pushing 400 watts of solar into the charge controller, when it's converted to 12 volts, it's going to put out about 30 amps, so you'll want to connect the charge controller to the battery bank with something like #8 awg wire or larger (if the distance is long). Once down to 12 volts from the charge controller, current will be very high.

Series or parallel has some impact on how the system will perform if one panel fails or one panel is in the shade.

2 x 200 watt panels in series is just fine.
The numbers above are rough estimates for illustration. Every system is slightly different, but once you have a number - 200 watts - and reasonable parity in solar panel performance - these numbers are close enough for government work.
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Old 02-08-2020, 10:02 PM   #20
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Series or parallel, that is the question. Simple answer - contact the manufacturer and see what they recommend. I followed my install instructions and went parallel. For mine, series was only used when going to a 24 volt set up.

This is a new one on me (retired electrician) too I normally wouldn't ever connect a 24 v charging source to a 12 v battery either. But I think something else is going on here, that charge controller is capable of various higher volts input up to whatever, 48, 72, don't know as this is new to me too. Now if the charge controller reduces its output to 12 v (nominal), that's all that matters is that it occurs before getting to the batt. .



That must be what is happening here, and makes sense to run the solar panels out to the controller at the highest volts possible. Since current is inversely proportional to volts, the wire with higher voltage will have less amps and line loss, and use smaller wire too. But after the controller, the lower output voltage will be under ohms law as well and bigger wire for the doubling of current (and greater line loss) will be in play.



Glad I read this thread as I now know to look for a controller that can take variety of volts input (maybe they all do ) and I'll likely go series with my pnls too.
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