Is my Victron charge controller the correct size?

[BobG-ESC]

We have a 12v battery system. Victron 100 volt MPPT controllers output 12 volts from any voltage up to 100 volts. We have a 100/50 controller.

Depending on who you want to believe, MPPT controllers are efficient down to about 15 volts, that's why many run two panels in series to get well over 15 volts (closer to 25 volts) so they harvest energy earlier/later in the day, and in shading. That's why Explorist Life and Mowgli Adventures advise to run two 12 volt panels in series first.

Best practice is to series identical panels for series or parallel, and get as close with VMP in parallel as possible. Some mismatched panels in series will have severe losses.

Enjoy,

Perry

The 200 watt panel Vmp is 37.6 volts and I assume 2 bypass diodes. A couple considerations to think about.

If one or more cells on one of the panels is partially shaded so that one of the 2 strings of cells on that panel is affected it will not produce voltage, the remaining string will only produce 18.8 volts max. In low light it will be less. So, in the morning or evening (if there happens to some shading) the voltage will be below the startup voltage for the controller which is +5volts more than the current battery voltage.

Two solar panels connected in parallel will operate at the lowest voltage panel so in effect, you won't be able to get power from either panel until the sun gets a little higher and then both panels will operate at 18 or a little more volts.

If connected in series and you get the same partial shading of a panel, you will get full output from the not shaded panel and 1/2 output from the partially shaded panel or a theoretical 300 watts at full sun.

Of course this is theoretical and an MPPT controller can help. Modern solar panels with bypass diodes connected in series is not the same as the old days.

If I am incorrect, I do not mind being corrected. I really do want to know how these things really work in real life. Mine are connected in series and seem to work well in shading situations but maybe they would work as well in parallel but as you see, I don't think so.

 

[GregWCIL]

Good luck with your test run tomorrow Perry.
One note: a complete calculator like Victron’s will also take into consideration panel temperatures. In cold conditions panel voltage can increase significantly and a series configuration can ruin the controller if it exceeds maximum rating.

 

[Centex]

an example relating to series vs parallel schemes

Just FYI relating to the series / parallel discussion ...

Here's the graphic output from the Victron VE-MPPT Calculator (rev. 4.0) showing three different schemes for an array (string) of four identical PV panels (Grape Solar GS-Star-200w) with the Victron SmartSolar MPPT 150|60 controller.

1. All four panels in parallel
2. Two pairs of parallel panels connected in series
3. All four panels in series

I like this calculator because the difference in Input voltage to the controller from the string (IOW, the string output) is readily apparent for each scheme and the controller-specific 'minimum Start voltage' is shown on the graph. But, it's only for Victron controllers and it does not readily accommodate arrays of 'mixed specification' panels.

This is of course with no consideration of partial shading which as Perry mentioned can have a significant impact on the real-world string output, particularly with panels in series.

IMO this helps demonstrate that no single connection scheme is likely to be 'ideal' for all circumstances, but in this specific case an all-parallel array seems to offer low risk of failure to achieve controller start voltage and would likely be most tolerant to (least compromised by) partial shading conditions. Yes, it is possible that the daily duration of charging may be slightly longer with one of the series schemes in horizon-to-horizon clear-sky situations.

IF one wanted to implement a 'most flexible' system one could route the output from each individual panel to a 'switching bus' where any of the three different parallel/series schemes could be selected to optimize for a given situation (I am not advocating that degree of system complexity).

(click the thumbnail then click again to enlarge to legible scale when viewing on a PC)

 

[Perry Butler]

The 200 watt panel Vmp is 37.6 volts and I assume 2 bypass diodes. A couple considerations to think about.

Yes, the VMP is 37.6 volts, but you didn't use 37.6 in your explanation below.

If one or more cells on one of the panels is partially shaded so that one of the 2 strings of cells on that panel is affected it will not produce voltage, the remaining string will only produce 18.8 volts max. In low light it will be less. So, in the morning or evening (if there happens to some shading) the voltage will be below the startup voltage for the controller which is +5volts more than the current battery voltage.

In the few days the 200 panels have been running the lowest voltage I've seen on my Victron 100/50 controller is in the lower 30’s and that was an hour or so before sunset. Most of the time it's 45-47 volts into the controller. You didn't keep in mind these are 24 volt category panels.

Two solar panels connected in parallel will operate at the lowest voltage panel so in effect, you won't be able to get power from either panel until the sun gets a little higher and then both panels will operate at 18 or a little more volts.

Again, these are 24 volt category panels, not 12 volt category, so double your voltage.

Because I purchased 24 volt panels there is no reason to run series to bring the voltage up. Once I had one panel running on the roof I observed the voltages and realized parallel was the best choice with 24 v panels, so wired them in parallel. With PWM being phased out for MPPT, I would expect to see installers going to 24 v panels, or even 48 v panels, and then 12 v panels will be phased out. Technology is always changing.

When connecting the second panel I had the panels shipping boxes cover the panels while I plugged and unplugged (I had one bad wire and had to make another). With both connected but only one covered I got virtually half the amps to the controller than when both were uncovered and the voltage remained the same. Parallel was doing its job, and that's what I was hoping to see.

I have not tried partially covering the panels to see the results, I would expect similar results.

If connected in series and you get the same partial shading of a panel, you will get full output from the not shaded panel and 1/2 output from the partially shaded panel or a theoretical 300 watts at full sun.

Same with 24 volt panels in parallel.

Of course this is theoretical and an MPPT controller can help. Modern solar panels with bypass diodes connected in series is not the same as the old days.

And a 24 volt panel will really eliminate the reason to have two 12 v panels in series to raise the voltage and the connect multiple two panel series strings together in parallel.

If I am incorrect, I do not mind being corrected. I really do want to know how these things really work in real life. Mine are connected in series and seem to work well in shading situations but maybe they would work as well in parallel but as you see, I don't think so.

You just kept going back to 12 volt evidence.

If you have 12v panels series make sense, unless you have more than three identical panels. At four identical panels you have each pair in series connected to the controller in parallel for better isolation.

With the old PWM controllers you had to have 12 volt panels, so only parallel made sense. With MPPT you could create two panel series strings to get the voltage up to 24 volt panels and wire two panel strings in series. Now with 24 volt panels the previous arguments for series are out the window on campers.

From what I've seen so far, 24 volt category panels are doing what I had hoped, and I can add one more panel to the roof (there is room for one more) and not be overvolting my Victron 100/50 controller.

I do realize by starting with a clean slate 24 volt made sense to me. I did remove the perfectly good 160 watt 12v panel that came with the trailer, but my son will make good use of that panel. Those of you with a single 12v panel on the roof will want another 12 v panel to keep expenses down.

Enjoy,

Perry

 

[BobG-ESC]

Perry, I was only considering a shading situation where a portion of one string of cells on a panel is partially shaded. In that case, the shaded string doesn't contribute voltage. The current bypasses that shaded string via a bypass diode. The specs for the Rich panel says they have bypass diodes but doesn't say how many. I assumed there were 2 so if one string of the 2 strings that make up a Rich panel has shading the voltage from that panel will be half of Vmp or 18.8 volts.

If there is no shading then it doesn't matter how they are connected; parallel, series, or a combination of parallel and series as Alen E. showed using the Victron tool that is used for selecting a Victron controller. Of course there is a small difference in that the higher current generated in the parallel scheme could create a little more voltage drop than the series scheme due to the higher current. Wire size could make this something to consider. Actually, because of advantages of running higher voltage, I use a 24 volt battery.

I have been under the impression that solar panels can be considered similar to batteries when designing the system in that if you connect a 24 volt battery and a 12 volt battery in parallel, it will spark because the 12 volt battery will act as a load. Connect them in series and they will deliver 36 volts. Solar panels are similar but have bypass diodes that may act as blocking diodes to prohibit the shaded cells from acting as a load when they are connected in parallel. However, I am not sure how the MPPT will handle the two voltages of 37.6 18.8. I have read that the system will operate at the lower voltage. In this case, 18.8 volts. I am not sure about this and that is what I would really like to know.

This link helps explain differences between parallel and series arrays when using modern solar panels and MPPT controllers.

I may run tests on mine to see if I can confirm what I think. I have 4x 160 watt panels in series and 2x 210 watt panels in series. Each array has its own MPPT.

It is also interesting to me that you are reading voltage higher than the specified Vmp of 37.6 volts.

 

[BobG-ESC]

... I may run tests on mine to see if I can confirm what I think. I have 4x 160 watt panels in series and 2x 210 watt panels in series. Each array has its own MPPT.

I tried to run tests by shading portions of cell strings on the 160 watt panels today. There are 8 cell strings (2 per panel) in series but I could only access 2 of the panels due to the way the trailer is parked.

Generally I always have shading on one cell string due to the air conditioner. The shading disappears for a very short time as the sun lines up on the center-line of the trailer. As the shade crosses over the output fluctuates up and down quite a bit for a while.

After adjusting for temperature, the voltage output per cell string matched up with the specifications and as I added shading to another string of cells the voltage would drop the prorated amount but not always. Sometimes the readings didn't make sense. One frustrating thing that sometimes happened when I shaded an additional string of cells, the voltage would drop but the current would go up a little. I wish I had taken screen shots instead of just writing down numbers because I don't trust what I wrote. Next time I will be better prepared to document what happens as I shade additional strings of cells.

 

[Perry Butler]

Perry, I was only considering a shading situation where a portion of one string of cells on a panel is partially shaded. In that case, the shaded string doesn't contribute voltage. The current bypasses that shaded string via a bypass diode. The specs for the Rich panel says they have bypass diodes but doesn't say how many. I assumed there were 2 so if one string of the 2 strings that make up a Rich panel has shading the voltage from that panel will be half of Vmp or 18.8 volts.

Using your logic for a 12v panel, then half of a VMP of 18 volts would be 9 volts and unusable. I don't think so. The voltage will remain the same.

We just got back from four days in a site with lots of shading. There was never the voltage drop you're talking about.

I may run tests on mine to see if I can confirm what I think. I have 4x 160 watt panels in series and 2x 210 watt panels in series. Each array has its own MPPT.

Yes, each different array should have it's own controller for best results.

Our two 200 watt Rich Solar panels go to a Victron 100/50 controller. Our 100 watt Renogy portable goes to a Victron 100/20 controller.

There is room for one more 200 watt Rich Solar panel that can be added to the other two in parallel, and room for two 150 watt panels. I doubt I'll ever install those two 150 watt panels but if I do then I'll have a third Victron controller under our dinette bench.

I'm hoping the 400 watts on the roof will be enough. On this short trip we found out Terry's new CPAP and other nightly used slightly under 40 ah's before solar started filling the batteries in the morning. With lots of shading we recovered around 20 ah's with the new panels, so after four nights we were down 80 amps on our 200 ah's of SOK batteries.

It is also interesting to me that you are reading voltage higher than the specified Vmp of 37.6 volts.

The specified VMP of 37.6 is merely a specification that outlines the lowest VMP to provide the claimed panel wattage. Good panels actually put out more watts than specified. Our four year old 100 watt portable has put out as much as 119 watts according to our Victron controller. Our 160 watt Carmanah panel (Canadian made) that came with the trailer put out as much as 180 watts this past winter. So far this past week the two Rich Solar 24v 200 watt panels put out 405 watts despite smokey skies from Canada and Minnesota fires when driving to our campsite, and the max voltage was 48.39 volts as can be seen in the screenshot below.

I was never impressed with the GoPower 160 watt panel on our 5.0. The most our Victron controller ever recorded was 155 watts. There are good panels and there are so-so panels.

Food for thought,

Perry

 

[BobG-ESC]

Today I was able to check the output of the 2 arrays consisting of 2S 210 watt array and the 4S 160 watt panel array. Both arrays performed as I expected. I only documented the 2x 210 watt array in this post because the other array is nearly always partially in shade which complicates documenting changes to shading. It did however adjust voltages as partial and full shading was added to panels as expected.

A screen shot of the output numbers for the 2S 210 watt panel array with no shade and a screen shot of of the output numbers for the same panels with both cell strings on one panel shaded. As you can see, the voltage and therefore power output is cut in half when half the series array is shaded.

In the picture taken inside the trailer you can see I have the water heater on for a load. Only the 2x 210 watt 2s array is turned on which is supplying 312 watts toward the 1366 watts needed for hot water. The battery is supplying the remainder. In order to activate the solar panels I put a load on the batteries because they were at 100% SOC. Unless on shore power, the water heater only comes on when SOC is above 95% which is after noon.

Two of the screen shots are of the output numbers for no shade and for full shade of one panel. You can see that the voltage in the shaded condition is 1/2 the no shade condition. The Vmp for the 210 watt panels is 33.54 volts.

This shows that solar panels with bypass diodes connected in series arrays do not shut down the array when a panel is shaded. The bypass diodes do pass the current around the shaded panel or cell string that is shaded as long as there is a proper bypass diode installed on the cell strings.

The purpose of this is not to say there isn't a place for solar panels configured in parallel because there is. It is often necessary to use parallel connections when configuring for optimal fit to an MPPT controller such as might be a 3S 2P configuration OR to meet the minimum voltage requirements of the controller/battery (I use 24 volt battery so the 160W panels have to be in series to have high enough voltage). A side benefit of series arrays with today's solar panels is they can sometimes be installed more efficient and less expensively than using a parallel configuration.

The main reason I responded to this thread is to help dispel the traditional thinking that solar panels must be configured in parallel arrays to function when shading is an issue.

 

[Ooshkaboo]

Today I was able to check the output of the 2 arrays consisting of 2S 210 watt array and the 4S 160 watt panel array. Both arrays performed as I expected. I only documented the 2x 210 watt array in this post because the other array is nearly always partially in shade which complicates documenting changes to shading. It did however adjust voltages as partial and full shading was added to panels as expected.

A screen shot of the output numbers for the 2S 210 watt panel array with no shade and a screen shot of of the output numbers for the same panels with both cell strings on one panel shaded. As you can see, the voltage and therefore power output is cut in half when half the series array is shaded.

In the picture taken inside the trailer you can see I have the water heater on for a load. Only the 2x 210 watt 2s array is turned on which is supplying 312 watts toward the 1366 watts needed for hot water. The battery is supplying the remainder. In order to activate the solar panels I put a load on the batteries because they were at 100% SOC. Unless on shore power, the water heater only comes on when SOC is above 95% which is after noon.

Two of the screen shots are of the output numbers for no shade and for full shade of one panel. You can see that the voltage in the shaded condition is 1/2 the no shade condition. The Vmp for the 210 watt panels is 33.54 volts.

This shows that solar panels with bypass diodes connected in series arrays do not shut down the array when a panel is shaded. The bypass diodes do pass the current around the shaded panel or cell string that is shaded as long as there is a proper bypass diode installed on the cell strings.

The purpose of this is not to say there isn't a place for solar panels configured in parallel because there is. It is often necessary to use parallel connections when configuring for optimal fit to an MPPT controller such as might be a 3S 2P configuration OR to meet the minimum voltage requirements of the controller/battery (I use 24 volt battery so the 160W panels have to be in series to have high enough voltage). A side benefit of series arrays with today's solar panels is they can sometimes be installed more efficient and less expensively than using a parallel configuration.

The main reason I responded to this thread is to help dispel the traditional thinking that solar panels must be configured in parallel arrays to function when shading is an issue.

So on my 5 there is room for one extra solar panel in front of my AC. I need to upgrade to a Victron MPPT then thought I could add a flexible panel in the spot in front of the AC.
I will have to search for the installs of the flexible panels, as I’m not ready for drilling thru the top. I do know there is a special tape some on here use. This could hopefully keep me from having to use my zamp port and carrying the extra panel.
If I’m understanding correctly…


Grasshopper-

 

[sherminator]

I will have to search for the installs of the flexible panels, as I’m not ready for drilling thru the top. I do know there is a special tape some on here use.

I recently installed two panels using VHB tape and following Mark B1's excellent instructions:

https://www.escapeforum.org/forums/f8/solar-system-with-flexible-panels-in-escape-19-a-17884.html

 

[Ooshkaboo]

I recently installed two panels using VHB tape and following Mark B1's excellent instructions:

https://www.escapeforum.org/forums/f8/solar-system-with-flexible-panels-in-escape-19-a-17884.html

That’s perfect, thx.

Now to make sure I get just the right panel, the 5 has only so much usable space on top.

 

[Perry Butler]

That’s perfect, thx.

Now to make sure I get just the right panel, the 5 has only so much usable space on top.

Every winter I run into people who have installed flexibles and most were new installs (within the last year). About half say they either failed or did not come close to delivering the watts advertised. You can easily add another rigid solar panel to the roof of your roof in front of the AC. I simply built my own brackets and installed with lots of VHB tape. I”m camping and on a iPad, and must go, but search for my thread where I installed three 100 watt panels on our 5.0. You just have to match the voltage and VMP of the new panel to your old. I added three 100 watt panels to our 170 watt GoPower and only lost 7 watts, when wired in parallel.

Food for thought,

Perry

 

[John in Santa Cruz]

my son ignored my advice and installed flexibles on his last camper (a surplus ambulance that had an absolutely flat top), and had them all fail within a year of broken internal connections.

I've had my rigid 360W panel for almost 2 years now, and about 20,000 miles, and zero probs. I had the factory 160W panel before that for about 5 years and I dunno how many miles, ditto no problems.