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Discussion Starter · #1 ·
I have (2) 200 watt Renogy solar panels currently installed:

Azure Rectangle Font Electric blue Parallel


I ordered an extra panel but it seems to have been changed between my last order and the new order:

Azure Rectangle Font Parallel Electric blue


How well will these work together?
 

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Discussion Starter · #2 ·
Is it:
Series is limited by minimum optimum current, and parallel is limited by minimum optimum voltage?

So,
Parallel would be:
19.2(8.85*2+10.42) = 540 watts

Series would be:
8.85(22.6*2+19.2) = 570 watts

So I'll "get" about 85% of the new panel's capacity added to my current setup (170/200 = 85%)?
 

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Discussion Starter · #3 ·
The above info was incorrect. It was supplied by Renogy as old and new versions G2 and G3. Perhaps I have G1 and G2.

New panel: 22.6V, 8.85A
Old panels: 21V, 9.52A (I set my phone camera on selfie with delay and slid it under the panel to photograph the label)

So
Parallel:
21(2*9.52 + 8.85) = 586W
Series:
8.85(2*21 + 22.6) = 572W

Slightly better, but I kinda want to do series to avoid buying several panel fuses and upgrading my main breaker.
 

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2014, 138WB, High Roof, Gas, SW MT
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Hi,
I think you might do a bit better than your calc for the parallel hookup.

If you have an MPPT (max power point tracking) charge controller, it will experiment around with the input voltage from the three PV panels until it gets the maximum power it can. It will likely be somewhere between the Vmps for the panels.

If you look at a typical IV diagram that shows the power output vs voltage, it will show that the power drops of slowly if you are not right at the Vmp of the panel. So, even though none of the three panels will be right at Vmp, they should all be generating near max power.

Rectangle Slope Plot Triangle Font

This generic IV diagram shows the Pmp (when the panel out voltage is at Vmp), but if you go a bit left or right of Vmp with the voltage the power does not drop much off the Pmp.

At least that's my guess :)

edit: If you have all three panels in hand, you could hook them up to the charge controller and a battery that is at low charge, and you could measure the input voltage to the charge controller and see where the charge controller sets it and maybe even see how the charge controller keeps changing the voltage to find the max power point. Of course, under real sun conditions the voltages and currents won't match the specs as the specs are taken under very favorable conditions - but, it would be interesting to see what the charge controller does. You could also try the series hookup and see how it handles that. Be careful on the series hookup that you don't exceed the max input voltage of the charge controller.

Gary
 

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The above info was incorrect. It was supplied by Renogy as old and new versions G2 and G3. Perhaps I have G1 and G2.

New panel: 22.6V, 8.85A
Old panels: 21V, 9.52A (I set my phone camera on selfie with delay and slid it under the panel to photograph the label)

So
Parallel:
21(2*9.52 + 8.85) = 586W
Series:
8.85(2*21 + 22.6) = 572W

Slightly better, but I kinda want to do series to avoid buying several panel fuses and upgrading my main breaker.
Not sure about the typical conditions that your setup runs at, but rarely do mine ever reach their full output current. Maybe a few moments in time on a very clear day, but most of the time the current on my test stand panels has been a lot less than the Imp rating. (especially in the winter and during fire season so 5 months right there)

Usually with an MPPT controller, you want to do whatever you can to have the (Vmp - Vbat max) at least 10 volts or more throughout most of the day. Vmp various a lot on solar panels based on sun angle, sunlight spectrum at that moment, etc, so don't count on it to be a constant.

@RV8R has made some posts in the past few months about the value of having the panels at his cabin in series / playing around with various setups.
 

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Not sure about the typical conditions that your setup runs at, but rarely do mine ever reach their full output current. Maybe a few moments in time on a very clear day, but most of the time the current on my test stand panels has been a lot less than the Imp rating. (especially in the winter and during fire season so 5 months right there)

Usually with an MPPT controller, you want to do whatever you can to have the (Vmp - Vbat max) at least 10 volts or more throughout most of the day. Vmp various a lot on solar panels based on sun angle, sunlight spectrum at that moment, etc, so don't count on it to be a constant.

@RV8R has made some posts in the past few months about the value of having the panels at his cabin in series / playing around with various setups.
Yup @HarryN & thanks to you I purchased a solar charger that is very capable of taking my panels in volts & amps. It is so easy to configure multiple panels of 2 in series/parallel & I believe especially with vans that are not only different weather & different locations it is best to have the option of whatever the van owner wants that day to suit the conditions.

The key is to buy a controller that can handle it & not run it @ 100% redline. You & I believe in the same things in regards to not designing components to run @ 100%.

My controller can handle 100v & the panels feed it about 60v max & 10a max = 600W. 6 -100W panels & the array has hit the 600W max - North of the 49th. 😁
 

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Discussion Starter · #7 ·
I noticed yesterday that if I'm facing east, the awning casts a couple inches of shade along the short edges. How bad is this?
  • I could shift the panels 2 inches to the left, and then they will look horrid from the street.
  • Or I could buy shallower unistrut, and remount the awning 3/4" to the right and 3/4" lower.
  • Or I could add some kind of spacers and raise all the panels a bit.
  • Or I could just leave it, try and park facing any other direction, and wait for spring when the sun rises higher in the sky.

Being lazy, I'm leaning towards the last option. My wife really hates the first option. Remounting the awning seems like the "correct" option, but dammit I am really feeling too lazy.

Sky Hood Automotive tire Grille Window
 

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Hi,
I would park facing east on a good sun day and when the shadow is on the panels and with your battery at a low state of charge. Note the PV panel power output (hopefully your charge controller tells you). Then immediately move the van so there is no shadow and note the power output. Repeat a couple times.
This will tell you how much you are actually losing do to the shadow.
If your charge controller does not have a watts in readout, you could measure the voltage and current into the charge controller and multiply them together to get watts in.

If when you are facing east, the shadow is only on the panel for the first hour or two of the day, then its not going to make much difference in daily power output. The solar power to the panel goes down with the cosine of the incidence angle of the sun, so when the sun is low (high incidence angle), you are not converting much of the suns power to electricity anyway. If the sun is (say) only 10 degs above the horizon, this is an incidence angle of 80 degs, and the cosine of 80 is 0.17, so you are losing 83% of the incident sun energy just do to the cosine effect. In other words, if there is no shadow most of the day, you probablyt won't even be able see the affect of the shadow on the daily output.

Gary
 

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I noticed yesterday that if I'm facing east, the awning casts a couple inches of shade
I agree with Gary. I wouldn't worry about it. That little awning shadow is highly dependent on (low) sun angle. It won't even be there most of the day. Lazy wins this round!
 

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Discussion Starter · #10 ·
The shadow is there all day currently with the low winter sun. I'll try the experiment on a weekend.
 

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Discussion Starter · #12 ·
Currently getting 195 watts according to the app.
62.5 volts, 3.1 amps
Sun angle 35 degrees and cloudy.

So I guess voltage is pretty much always at or around optimal, but current goes down with less sun? In that case it seems like I don't really have to ever worry about being limited by the 8.85A current of the new panel if I never drive to the tropics at noon in the summer.
 

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Not sure about the typical conditions that your setup runs at, but rarely do mine ever reach their full output current. Maybe a few moments in time on a very clear day, but most of the time the current on my test stand panels has been a lot less than the Imp rating. (especially in the winter and during fire season so 5 months right there)

Usually with an MPPT controller, you want to do whatever you can to have the (Vmp - Vbat max) at least 10 volts or more throughout most of the day. Vmp various a lot on solar panels based on sun angle, sunlight spectrum at that moment, etc, so don't count on it to be a constant.

@RV8R has made some posts in the past few months about the value of having the panels at his cabin in series / playing around with various setups.
Hi Harry,
Just to add to the fund of not so important knowledge on how PV panels actually do...

I live at 5000 ft elevation in pretty good air quality MT.
I occasionally get the full rated power out of my home PV panels, and this is with the inverter loss included, so the panels are actually producing more than their rated power (a little).

When panels are rated under the STC system, they provide 1000 watt/sq meter sun and keep the the panel surface at 25C. Both of these are optimistic, but they do occur on occasion.
I have a lab quality pyranometer and have seen solar intensities all the way up to 1200 watts/sq meter (20% more than "full sun"). Some of our best solar days are very clear and cold winter days - good sun and cold panel temps. My panels are tilted at 45 degs, so close to perpendicular incidence around noon.

Unfortunately these conditions don't occur very often.

Gary
 
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