MPPSolar mppt regulator (parallel or series?)

[Techno]

Today in good morning Sun (early April) I have connected 2x100watt monocrystaline solars to a 200 watt MPPsolar mppt regulator in both series and parallel with in clear sky and full cloud.

The scene
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The regulator shown with battery under load and solars covered.
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The constant load
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Series connection with one panel covered.
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Output
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with both panels
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output
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connections in series
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Now changed to parallel
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Output no significant difference but if anything a tad better.
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Same sky throughout test covering around 15 minutes
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Later after discharging battery and sky completely clouded.
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Series
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Parallel
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same light throughout
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My conclusion is there is no benefit to connecting 12 volt panels in series as clearly the output is actually better in parallel with these units.
So the only point to the spec of this regulator is that it will accept 24volt panels which can be an advantage if they are available at the right size/price but even then probably best connected in parallel.

 

[hilldweller]

Can't beat a bit of real world research. Nice one.

 

[Techno]

Yes Brian this is where I check and compare regulators
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[Popeye]

Yes Brian this is where I check and compare regulators

Andy, I think I have admired almost all of the work you have done and advice you have given, but sometimes fellow Funster I think.........

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[gus-lopez]

Andy, I think I have admired almost all of the work you have done and advice you have given, but sometimes fellow Funster I think.........

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Could fill them plant pots ?

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[wizzer59]

 

[hilldweller]

Could fill them plant pots ?

He would if he could find a circular panel.

 

[Techno]

Could fill them plant pots ?

I'm in the process of jet washing and re oiling the decks so no point creating more stuff to shift just yet

 

[Techno]

Usually looks like this and we can't get much further off topic although it could be regarded as Sun related

 

[DBK]

Interesting result although why there is a significant difference when it is cloudy seems odd. Do you know what the explanation is or was it perhaps just a fluctuation in the cloud level?

But whether putting them in parallel is right for every MH depends perhaps on whether you are going to use any existing wiring. For example, if a MH already has a panel and the wiring going to the controller is sized for that panel it may be better, if adding a second panel, to add it in series so the current remains the same. If fitting new thicker wiring perhaps parallel is better.

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[Techno]

Probably a slight change in light level.
Whether it is one two three or more panels most installers use a minimum of 4mm so adding a panel makes no difference. If anything wiring in series requires smaller cable than in parallel.EDIT like you said

 

[Lenny HB]

Providing reasonable size cables are used I don't worry too much about cable size. On my van I have 2 x 100 Watt panels in parallel, cable run is about 5m I only used 4mm cable. Working on the theory that in mid summer I can get a max output of around 10 amps with 4mm cable about 5% loss or 0.5 amp, not worth worrying about. In winter winter with say 4 amps output the loss will be 2% or 80ma again not worth worrying about.

 

[eddie]

In a "solar farm" situation that is static, I would (if asked) advise that in series is preferable. There is a slight advantage. On a motorhome that potentially could face a new "position challenge" every time the motorhome is moved, I would resort back to parallel.

In series, if one panel is in shade in the morning, and say the other "(assuming that there are two panels fitted) is in shade in the afternoon, you'll have a problem.

In parallel the worst case is that you would only potentially benefit from the output from one panel.

Great photos, and excellent advice Andy

 

[Don Quixote]

Great post, enjoy reading and looking at pictures on this subject. Thanks

 

[OldAgeTravellers]

Great Post Andy, thanks very much. sorry I am a bit late to the party. Unfortunately there are obviously limitations because you only had one set-up.
Unfortunately it does not answer the question I would have liked answered.
I always assumed in normal conditions there was no benefit between the two except that I believe that in series the cut in voltage of the controller would be achieved sooner andcontinued longer so perhaps the series would switch on and start charging at say 8am and switch off at say 7pm whereas the parallels connection would be some time after switching on and some time earlier switching off. At a certain light level the panels would be producing say 9volts so in parallel the controller would see 9 volts and not switch on but in parallel the controller would see 18 volts so would be producing a charge. That is the only reason for my belief in parallel connection. In fact I once met a German guy parked up under a street lamp in Paris who swore that he was getting a charge from the street lamp (I didn't chech his controller) and he was sure that it was because he had an MPPT controller and his panels were wired in Paralel. It would have been good if you could have tested this point but it would of course mean two setups to be meaningful. But thanks for the, as usual, great write up. If at some point though you find yourself with four identical panels and two MPPT controllers and a couple of batteries it would be great if you could test it out until them I remain convinced that series is best if the controller can take the maximum possible voltage of the panels.
Regards,
Steve

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[DBK]

Great Post Andy, thanks very much. sorry I am a bit late to the party. Unfortunately there are obviously limitations because you only had one set-up.
Unfortunately it does not answer the question I would have liked answered.
I always assumed in normal conditions there was no benefit between the two except that I believe that in series the cut in voltage of the controller would be achieved sooner andcontinued longer so perhaps the series would switch on and start charging at say 8am and switch off at say 7pm whereas the parallels connection would be some time after switching on and some time earlier switching off. At a certain light level the panels would be producing say 9volts so in parallel the controller would see 9 volts and not switch on but in parallel the controller would see 18 volts so would be producing a charge. That is the only reason for my belief in parallel connection. In fact I once met a German guy parked up under a street lamp in Paris who swore that he was getting a charge from the street lamp (I didn't chech his controller) and he was sure that it was because he had an MPPT controller and his panels were wired in Paralel. It would have been good if you could have tested this point but it would of course mean two setups to be meaningful. But thanks for the, as usual, great write up. If at some point though you find yourself with four identical panels and two MPPT controllers and a couple of batteries it would be great if you could test it out until them I remain convinced that series is best if the controller can take the maximum possible voltage of the panels.
Regards,
Steve

Following your logic, which I like, series should be better as under poor light the two 9 volts would be added to make 18, making enough for a charge?

However, I am not sure PV cells work like that, I think under low light levels they still produce a highish voltage but they can only produce a low current.

 

[TheCaller]

Correct, but a low current is better than no current at all. Very useful when a van is standing in winter without moving for a few weeks & no access to EHU. At least it will start when you get back to it.

To be fair, it would be a pretty awful winter if parallel panels didn't manage this too.

My winter use of the van is the about the worst possible - occasional short distance trips, overnight stays & no EHU.

 

[OldAgeTravellers]

Hi DBK,
I am sure panels slowly increase their voltage from a switch on point which is around the 9 volts as the light level increases up to the maximum of around 17 volts which is the usual open circuit maximum, but can't find the reference to it at the moment, but of course you don't see it because the controller does not pass current until the voltage can be above the batteries. The actual benefit may be tiny which is why I would have liked to see it in Andy's tests but as I said, it would only be meaningful if there were two identical setups, one in series one in parallel to compare. But of course I may be totally wrong with the last few brain cells left finding the wrong bit of data.
Steve

 

[tonyidle]

Hi DBK,
I am sure panels slowly increase their voltage from a switch on point which is around the 9 volts as the light level increases up to the maximum of around 17 volts which is the usual open circuit maximum, but can't find the reference to it at the moment, but of course you don't see it because the controller does not pass current until the voltage can be above the batteries. The actual benefit may be tiny which is why I would have liked to see it in Andy's tests but as I said, it would only be meaningful if there were two identical setups, one in series one in parallel to compare. But of course I may be totally wrong with the last few brain cells left finding the wrong bit of data.
Steve

I'm not certain that the panel voltage needs to be above that of the batteries. That was always the case with simple controllers but is it the same with MPPT? There is no need for that to be the case and I thought that an MPPT controller was able to use whatever power (AxV) was available.

 

[bubble63]

the whole idea is that a MPPT controller inverts the the DC steps it up and then rectifies it back to DC at a higher voltage to charge the battery
electricity won't flow up hill, i.e. 11 volts won't go into a 12v battery it has to be 12.1v or more to go in
I think
so in effect on a dull day the panel produces 10v, say, the MPPT gets it higher to go into the battery, of course OHM's law means the amperage will be less, but hey ho its charging when an ordinary charger wouldn't be.

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[Techno]

The mppt regulator does not switch on until it gets 15volts from the panels

 

[Techno]

In winter I get by because I have a lot of batteries but even so after 5 days I would have to hook up to fully charge them. In storage I will get enough to keep them full through the winter.
For the best part of the year I know I am getting a better output in parallel and that is what counts for me and as I've said I could not connect my three panels in series

 

[Techno]

If I didn't use the inverter I could probably last a few weeks in winter

 

[OldAgeTravellers]

Yes Andy, as I said in series the panels will reach the switch-on voltage of the MPPT much quicker and switch of much later. You are an exception really because you carry half a tonne of batterers. We have two 90ah (110ah ) and try to be off grid as long as possible so a few very cloudy days could really drain our power. I only have two panels so the MPPT can easily cope with series connection.
I don't really think your test actually proved parallel best because you only had one setup so it was impossible to know that the cloudy period was the same for both.
The theory says series should be better over all in that for any given circumstances series will be supplying a charge for longer (even perhaps from a street lamp!) but it would be nice to actually see it in a real world test.
Mind you it would be nice to find a good reasonable supplier of good quality panels so I can replace mine which are down to below 30% output. The last German one I tried turned out to be a B****r any suggestions welcome but we are in France so delivery is often a problem for most suppliers. Then I wouldn't be scraping around for any odd milliamp I can find.
Steve

 

[tonyidle]

the whole idea is that a MPPT controller inverts the the DC steps it up and then rectifies it back to DC at a higher voltage to charge the battery
electricity won't flow up hill, i.e. 11 volts won't go into a 12v battery it has to be 12.1v or more to go in
I think
so in effect on a dull day the panel produces 10v, say, the MPPT gets it higher to go into the battery, of course OHM's law means the amperage will be less, but hey ho its charging when an ordinary charger wouldn't be.

You are correct that at the output of the regulator the voltage available must exceed the terminal voltage of the battery. And I had assumed that the MPPT regulator does exactly what you suggest.

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[Peter A Forbes]

The Maximum Solar MPPT controller that Andy and I both use has two conversion sections, one processing the solar input and one the DC output to the batteries.

The panels need to be kept at their most efficient output voltage range, so the controller processes the input, keeping its loading such that it leaves the panel running at its optimum range of output.

The second half basically is a switch-mode power supply configured as a 3-stage battery charger.

Peter

 

[tonyidle]

The Maximum Solar MPPT controller that Andy and I both use has two conversion sections, one processing the solar input and one the DC output to the batteries.

The panels need to be kept at their most efficient output voltage range, so the controller processes the input, keeping its loading such that it leaves the panel running at its optimum range of output.

The second half basically is a switch-mode power supply configured as a 3-stage battery charger.

Peter

Again - what I've always assumed for MPPT. Thanks for confirmation.

 

[sweetie]

Slightly off thread but how is the Mercedes conversion coming along Peter? Missing your updates.

 

[DBK]

Yes Andy, as I said in series the panels will reach the switch-on voltage of the MPPT much quicker and switch of much later. You are an exception really because you carry half a tonne of batterers. We have two 90ah (110ah ) and try to be off grid as long as possible so a few very cloudy days could really drain our power. I only have two panels so the MPPT can easily cope with series connection.
I don't really think your test actually proved parallel best because you only had one setup so it was impossible to know that the cloudy period was the same for both.
The theory says series should be better over all in that for any given circumstances series will be supplying a charge for longer (even perhaps from a street lamp!) but it would be nice to actually see it in a real world test.
Mind you it would be nice to find a good reasonable supplier of good quality panels so I can replace mine which are down to below 30% output. The last German one I tried turned out to be a B****r any suggestions welcome but we are in France so delivery is often a problem for most suppliers. Then I wouldn't be scraping around for any odd milliamp I can find.
Steve

I've done a bit more research and it seems my instincts were more or less right. The graph of output voltage against light level (lux) isn't a straight line, it is a very marked hockey stick. The open circuit voltage climbs from zero to about 70% of maximum right at the start of the graph and then curves and levels off fairly quickly. This means for any usable levels of light a low output voltage shouldn't be an issue. They may not do anything under a street light but even if they did the power would negligible. Even a 100W streetlight would only cast a few watts on an individual panel at best. Just imagine a sphere around the street light and what tiny fraction of the total area of the sphere the PV panel(s) are and you will appreciate even a single watt might be expecting too much.*

All the references I could find were PDFs so I won't post a link but if you Google "photo voltaic cell voltage lux" you should find a few graphs.

Which isn't a full answer to the question but given there are other factors, such as one damaged panel having perhaps a greater impact on the other when connected in series I think determining the optimum arrangement isn't straightforward.

Edit: Just done the sums. If the streetlight was 5m above the panel the surface area of the sphere is 314 square metres. So for every square metre of PV panel it could potentially harvest about 0.3% of the total power radiated by the street light. Of course not all the power going into the streetlight is converted into light, much must be lost as heat and PV cells are only around 20% efficient. So if you are parked under a 100W streetlight with a couple of 100W panels, which would be about a metre square in total you wouldn't get enough energy from the streetlight to power the smallest led bulb. Of course streetlights don't shine evenly in all directions but even taking the most optimistic estimates and taking the distance between the panel down to 2 metres (area 50 sq m) garnering even a single watt from a streetlight is nigh on impossible with any typical MH solar array I think.

 

[Peter A Forbes]

Slightly off thread but how is the Mercedes conversion coming along Peter? Missing your updates.

Not much done as I had the heart operation at the end of July, so the drugs before and the recovery after have stopped any serious work.

We started back on it a week or so ago, and things are gradually winding back up.

Here's the current layout plan:

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Probably best to click on it to get a better view.

Got to sort the new windows out before the winter arrives!

Peter

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