Adding to or changing an existing solar panel layout.

[peterc10]

When we bought our Hymer new back in 2015 the dealer agreed to put in 250W of solar panels wired in parallel. They did that by using what they said was a 100W and a 150W panel. I have no knowledge of what these panels are or who made them. A few months ago I noticed strange marks, like burn runs under the glass on the larger panel and so I asked the experts here what they thought of them. The consensus was that these occasionally occur but nobody was sure whether or not they reduced the power produced. I have looked again and these marks are spreading.

Now I am looking to increase my solar power to 350W, which is the maximum our new Votronic regulator is supposed to take. On looking at the large panel again I noticed that it was a bluey colour and had a different look to the smaller black one. Looking on the internet it now seems that this larger panel was probably a less efficient polycrystalline panel rather than the monocrystalline smaller one. So rather than just adding another 100W panel I am thinking of replacing the probably failing 150W panel with a larger one, which would mean I could use the same wiring.

But I would like some advice on this and have some questions for all you experts.

1 Both of my panels have 36 cells in a 9 x 4 layout. Am I right in thinking that the number of cells on the panel decides the voltage and the size of the cells decides the current? If so do I just need to get a panel with the same number of cells they should be compatible, i.e. of the same voltage, with the one I am keeping. And in doing so do I need to maintain the 9 x 4 layout?

2 Looking at Ebay I can see that I can buy a 250W monocrystalline panel that is physically smaller than the 150W polycrystalline one it is replacing. But, more interestingly, I can get a 300W one for another £24 that is almost exactly the same size as the existing one. This means that I can probably use the existing aluminium angle mounts, which would make the job much easier. But this would also mean in theory that I could be putting in a total of 400W which is 50W more than the maximum the Votronic regulator is supposed to take, It has a 30A fuse. Given that I am not going to go anywhere near the equator, is this likely to give me a problem?

3 The panels I am looking at are made by Tatoodaa and are supposed to be "German Certified" whatever that means. Have any funsters bought these panels and if so are they OK?

Many thanks for any help you can give.

Lenny HB Raul autorouter

 

[Raul]

The bigger the panel the better if you have space. However your panel VOC it’s limited by your controller capability. You have to have a look at max VOC of your controller, and then make sure the panel does not exceed that. Ex a 60 cell panel VOC 37v wil kick out in cold -15 ish, about 44,4voc. The colder it gets the higher the voltage. So, this 60cell panel it’s ok in paralel on a controller with max voc 50v or series on a controller with 100v like victron 100/30-100/50 etc.

First find you controller max voltage in, then decide what panel cell arrangement you go for.

 

[peterc10]

The bigger the panel the better if you have space. However your panel VOC it’s limited by your controller capability. You have to have a look at max VOC of your controller, and then make sure the panel does not exceed that. Ex a 60 cell panel VOC 37v wil kick out in cold -15 ish, about 44,4voc. The colder it gets the higher the voltage. So, this 60cell panel it’s ok in paralel on a controller with max voc 50v or series on a controller with 100v like victron 100/30-100/50 etc.

First find you controller max voltage in, then decide what panel cell arrangement you go for.

Thanks Raul. The panels are wired in parallel and that is what I will keep. I need to match the voltages of the existing panel and the new one if I want them to work best together don't I? The existing one is a 36 cell unit in a 9 x 4 layout and the new one will be the same. So will they both have the same VOC of about 22V (pro ratting your 37v figure for 60 cells)? Although I am not sure where you got the 60 cell suggestion from.

Votronic says that the maximum VOC is 50v, which is well inside. But they also say that the maximum power should be 350W, whereas mine would be 400W (100W existing and 300W new). Will that small increase matter practically given that the panels will rarely, if ever, work to their maximum power output? Votronic also say the maximum current should be 21A, but they have fused it at 30A.

 

[RustyRuss]

My experience is that you need the outputs to be very close together as the weakest panel dictates how much energy yo can take from the sun and convert into stored energy in your battery/ies.

Cheers!

Russ

 

[cmcardle75]

If it was a Victron MPPT, you could just knock yourself out. It just throws away any marginal over current. Votronic, I'm not sure about.

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[Reallyretired]

If they are in parallel the voltages need to be the same to be efficient.
I don't think in practice the extra 50w would matter at all it would be a rare sunny day for you to get more than 21A and certainly not more than 30A.

 

[peterc10]

If they are in parallel the voltages need to be the same to be efficient.
I don't think in practice the extra 50w would matter at all it would be a rare sunny day for you to get more than 21A and certainly not more than 30A.

I agree about the voltages being the same, which is why I want to make sure that it is the number of cells, not their size, that determines the VOC.

I will check what the voltage is going into the regulator tomorrow. Will that be the same as the VOC?

If it was a Victron MPPT, you could just knock yourself out. It just throws away any marginal over current. Votronic, I'm not sure about.

I have just checked the Votronic specification and it says it has a "Limitation of Charging current/Overload Protection" installed. Is that what you are referring to?

 

[autorouter]

I will check what the voltage is going into the regulator tomorrow. Will that be the same as the VOC?

Yes. Voc is the 'open circuit' voltage, when the wires are not connected to anything, and that's when the voltage is highest. When connected to the controller, you are concerned with Vmp, the voltage when it's giving out maximum power. But there's really not much difference.

On a MH, panels are usually fixed flat to the roof, so they are not tilted at the optimum angle to the sun. In that situation you won't get more than about 70%, maybe 80%, of the nominal panel power. If by any chance it goes over the limit by 20% or so, the controller will just dump any excess.

 

[Raul]

So the votronic can take 50v and 21A, theoretically it can modulate ANY power within this limits, but output will always be limited to 30amps times battery voltage. The 400w it’s not a issue as it will modulate to take in what the battery needs. The 30a refers to output, that’s why is fused at 30. At input it does not have protection, that’s why you don’t exceed the 21a ( 3 panels of 8a in parallel max), and respectively the 50VOC open circuit voltage.
Two panels of 22v in cold will kick out 22x2x1.2= 50.6v at -20C and. 49.28v at about -15-17C deg. This is valid if temp coefficient of the panel does not exceed 0,40%/C. Victron panels have a very big coefficient as a example 0.47%/C deg. And some other panels as low as 0.27%/ C. The smaller the coefficient the better. It means the voltage is more stable when temps move above or below test condition at 25C deg.

 

[autorouter]

Two panels of 22v in cold will kick out 22x2x1.2= 50.6v at -20C and. 49.28v at about -15-17C deg.

That's with the panels in series. When in parallel, it's only half of that, so no problem.

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[peterc10]

Does the VOC or VMP differ based upon how much sun they are getting? Today is cloudy at the moment and I am getting 19.99V across the terminals for VMP. Does that sound right for 36 cell (9 x 4) panels? What is confusing me is that panel I am thinking of buying appear to be the same 36 cell layout, but their spec says the VMP is 39.7V. That seems to suggest that it is not the number of cells that dictate the voltage. Or that the photo of the panel is not the one they are selling!

Am I right to think that if the VMP of the new panel is 39.7v it will be dragged down to the VMP of the existing panel and therefore the wattage would decrease?

 

[cmcardle75]

Does the VOC or VMP differ based upon how much sun they are getting? Today is cloudy at the moment and I am getting 19.99V across the terminals for VMP. Does that sound right for 36 cell (9 x 4) panels? What is confusing me is that panel I am thinking of buying appear to be the same 36 cell layout, but their spec says the VMP is 39.7V. That seems to suggest that it is not the number of cells that dictate the voltage. Or that the photo of the panel is not the one they are selling!

Am I right to think that if the VMP of the new panel is 39.7v it will be dragged down to the VMP of the existing panel and therefore the wattage would decrease?

Can you actually see how they're wired from the photo?

 

[autorouter]

What is confusing me is that panel I am thinking of buying appear to be the same 36 cell layout, but their spec says the VMP is 39.7V. That seems to suggest that it is not the number of cells that dictate the voltage. Or that the photo of the panel is not the one they are selling!

That's a possibility, very often on websites the photo is just a generic one. When you said a 300W 9 x 4 panel I thought it sounded unusual. Panels of 250 or 300W are usually 60-cell or more. Unless the cells in the 36-cell panels are unusually large.

I have the impression that solar cells are manufactured using silicon chip facilities that are out-of-date, having moved on to ever larger silicon wafer sizes. At some stage they will be using the 12-inch wafer stuff for solar cells, and I thought that had started happening already. But apparently not.

 

[Raul]

Does the VOC or VMP differ based upon how much sun they are getting? Today is cloudy at the moment and I am getting 19.99V across the terminals for VMP. Does that sound right for 36 cell (9 x 4) panels? What is confusing me is that panel I am thinking of buying appear to be the same 36 cell layout, but their spec says the VMP is 39.7V. That seems to suggest that it is not the number of cells that dictate the voltage. Or that the photo of the panel is not the one they are selling!

Am I right to think that if the VMP of the new panel is 39.7v it will be dragged down to the VMP of the existing panel and therefore the wattage would decrease?

The vmp it’s what you reading. Voc it’s only present at controller when it wakes up, or when it does not charge. The mppt moves the power curve to max voltage to not charge because it reached constant voltage.

The panel you are referring to with the vmp 39,7v it can be half cut cells, shingles or amorphous. It will definitely get dragged down to the smallest vmp of the other panel.
Can you put a link of the panel you talking about?
A 36cell panel has about 22v voc, and about 18-19vmp.

 

[irnbru]

1 Both of my panels have 36 cells in a 9 x 4 layout. Am I right in thinking that the number of cells on the panel decides the voltage and the size of the cells decides the current? If so do I just need to get a panel with the same number of cells they should be compatible, i.e. of the same voltage, with the one I am keeping. And in doing so do I need to maintain the 9 x 4 layout?

Peter can you confirm if you are saying you can tell the current /amp output from the size of the panel? Only asking so I could try working out the size of mine. Ive no idea if its a 120w or 150 W and would be good to know.

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[Raul]

That's a possibility, very often on websites the photo is just a generic one. When you said a 300W 9 x 4 panel I thought it sounded unusual. Panels of 250 or 300W are usually 60-cell or more. Unless the cells in the 36-cell panels are unusually large.

I have the impression that solar cells are manufactured using silicon chip facilities that are out-of-date, having moved on to ever larger silicon wafer sizes. At some stage they will be using the 12-inch wafer stuff for solar cells, and I thought that had started happening already. But apparently not.

The bigger the cel, the bigger the ingot has to be from where they get cut. Bigger cost, and out of a set standard already. Solar cells actually gone smaller with half cut, it’s less waste from the ingot for mono.
What we see is, overlap of cells ( shingles) that eliminates the space between the cells with ribbon overlapped buss bar. Also most big panels are half cut, and you get a 120 cell but 60x 2 in paralel 60S 2P. These have a vmp of 40v and double the current of small 5” cells. It’s been proven that smaller cells yield a more efficient panel due to less resistance and higher voltage. SunPower an panasonic stuck to 5” cell unlike the rest.

 

[peterc10]

The vmp it’s what you reading. Voc it’s only present at controller when it wakes up, or when it does not charge. The mppt moves the power curve to max voltage to not charge because it reached constant voltage.

The panel you are referring to with the vmp 39,7v it can be half cut cells, shingles or amorphous. It will definitely get dragged down to the smallest vmp of the other panel.
Can you put a link of the panel you talking about?
A 36cell panel has about 22v voc, and about 18-19vmp.

Thanks. Those figures for Vmp are about what our existing ones are doing.

This is the item that is listed The first picture clearly shows a 9 x 4 array, but some other don't. I may have to rethink what I am going to do.

That's a possibility, very often on websites the photo is just a generic one. When you said a 300W 9 x 4 panel I thought it sounded unusual. Panels of 250 or 300W are usually 60-cell or more. Unless the cells in the 36-cell panels are unusually large.

I have the impression that solar cells are manufactured using silicon chip facilities that are out-of-date, having moved on to ever larger silicon wafer sizes. At some stage they will be using the 12-inch wafer stuff for solar cells, and I thought that had started happening already. But apparently not.

I may have to rethink matters if that is the case. Alternative is to keep the existing small one get 2 new panels i.e. 1 x 100W and 1 x 150/200W. Or I could get rid of both of the existing panels I have got and go for 1 x 350/400W or 2 x 200W.

Decisions decisions ..........

Peter can you confirm if you are saying you can tell the current /amp output from the size of the panel? Only asking so I could try working out the size of mine. Ive no idea if its a 120w or 150 W and would be good to know.

No I am not sure you can with any accuracy as I have seen panels of varying sizes with the same power outage. All you can tell is the voltage of them by the number of cells. But you also need the current they produce to calculate their wattage.

 

[peterc10]

The bigger the cel, the bigger the ingot has to be from where they get cut. Bigger cost, and out of a set standard already. Solar cells actually gone smaller with half cut, it’s less waste from the ingot for mono.
What we see is, overlap of cells ( shingles) that eliminates the space between the cells with ribbon overlapped buss bar. Also most big panels are half cut, and you get a 120 cell but 60x 2 in paralel 60S 2P. These have a vmp of 40v and double the current of small 5” cells. It’s been proven that smaller cells yield a more efficient panel due to less resistance and higher voltage. SunPower an panasonic stuck to 5” cell unlike the rest.

Thanks for that Raul.

The wooshing you have just heard is nearly all of that going over my head.

 

[I2C]

This is a good site to visit, it explains the good and bad points of adding non-matching solar panels in serial and parallel configurations.