Is it possible to have two solar panel connected (in parallel) to smart solar 100/20 ?

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iostrym asked Mar 23, '20

Is it possible to have two solar panel connected (in parallel) to smart solar 100/20 ?

I have already a solar pannel connected to my smartsolar 100/20 and I want to add a new one.

First solar pannel is 185 WC (24v, 72 cells) Voc = 44.21V Isc = 5.59A

Second one is not yet bought and may be a luxor 200 Wc (24v, 72 cells) Voc = 44.27V Isc = 5.87A

I know that smarsolar 100/20 has a 100 V limit for solar pannel voltage and this is ok with my solar pannel parallelly connected.

Output for load of battery is 20 A max. Battery are 12V ones connected in parallele.

I don't know how to calculate maximum power that could enter in the 100/20. Could it be :

185+200 = 385 W => maximum intensity provided to 12V batteries would be 385 W/12 = 32A.

right ? so it won't be ok with my 12V batteries because 100/20 can load only 20A max, right ? I need to connect my batteries in serial to have 24V and then less intensity. Is my calculation correct ?

MPPT Controllers Solar Panel

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Answer 1 · 2020-03-23T18:05:11Z

Alexandra answered · Mar 23, 2020 at 06:05 PM

@iostrym

https://www.victronenergy.com/mppt-calculator or

https://www.victronenergy.com/upload/software/VE-MPPT-Calc-3_4.xlsm

This is a good place to start. But generally speaking when connecting panels to one charge controller you would want to match them not have two different sizes/module types.

It is possible to connect them as you are describing, but not recommended. Check out this article on mixing panels.

https://solarpanelsvenue.com/mixing-solar-panels/

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Answer 2 · 2020-03-23T18:26:37Z

justme answered · Mar 23, 2020 at 06:26 PM

In series you need the max amps to be as close as possible & understand that the max amps is limited by the lowest value. Effectively you will have two panels at 5.59 amps.

In parallel you need the volts to match.

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Answer 3 · 2020-03-24T11:30:31Z

Warwick Bruce Chapman answered · Mar 24, 2020 at 11:30 AM

Yes it will work but you will effectively have two 185W panels.

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Answer 4 · 2020-03-26T23:39:12Z

iostrym answered · Mar 26, 2020 at 11:39 PM

Hello all thanks a lot for your answers.

I didn't understand your answers and this is because I was wrong when I said that solar pannel would be serially connected.I would like to connect them in parallel, not in serial. This is why I will correct my first message. sorry guy for all your answers.

I would like to avoid serially connection because I will be limited to the lowest value as you said. if one has no more sun, then it will shut off current even if the second one has a lot of sun.

Also I think I will buy a 350 WC solar pannel so I really don't want to be limited by current of the small pannel.

But I need to know if my undertanding about maximum current delivered to batteries is correct...

20A maxi delivered to batteries using 100/20, right ?

Also, is smartsolar 100/20 smart enought to limit by itself current to batteries at 20A or will the smartsolar 100/20 be damaged by too much current ?

ps : I'm not afraid of loosing current because I'm in a situation where there is not 100% sun on my solar pannel because there are badly placed (not in correct angle and exposition) so I'm not sure that I will really reach 350WC... But I need to understand exactly how it works.

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Answer 5 · 2020-03-27T23:17:39Z

iostrym answered · Mar 27, 2020 at 11:17 PM

@Alexandra, thanks for your link https://solarpanelsvenue.com/mixing-solar-panels/ but there is one part that I don't understand regarding parallel connection :

chapter : "Wiring solar panels of different ratings in parallel"

in this schematic, it is assumed that all solar panel are working at their maximum power point but it is impossible in parallel, as voltage would be choosen by charge controller to track maximum power voltage common to all solar pannel. it is impossible to have one panel at 17 V and other panel at 19V as indicated in the schematic. total current won't be 4x8A as other solar pannel will work at a voltage that is different to their own maximum power voltage. it will be the maximum power voltage of the complete system right.

So my point is :

- I agree that having identical solar pannel is the best. but it is impossible to do this if, like me, you add a new solar pannel 10 years after the first one.

- I agree that i will have maximum power if I buy a dedicated charge controller for each panel. (but I don't want to)

- with parallel connection : I have the feeling that adding a new solar pannel will be always better that keeping only the old one. and also I have the feeling that buying the new solar pannel + keeping the old one will give better result that keeping only the new one. => Am I wrong ?

And finally, what would be solar pannel specification to check if I want to minimize the power lost when using two solar pannel connected together in parallele regarding the power I could get if I connect each one on a separate charge controler. Only check Vmp voltage ? Is Voc important ? or cell numbers ? or something else ?

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Alexandra ♦ commented · Mar 28, 2020 at 09:44 AM

@iostrym I propose an experiment to help you understand if you have the time.

1) Set up the old panel with the charge controller for a day or so in your system - check your yield. You may find its performance is not as great as it could be.

2) Remove the old panel, set up your new panel with the charge controller in your system - Check your yield.

3) Set up the system with them in series, then in parallel - check your yield.

You will have a smart charge controller so the daily usage history will be recorded. Then go with the one that yields the best result.

What you may find is the older panel has degraded and that it will dissipate power from the new one and bring the yield down.

To answer the question about the parallel connection the system will track the power point of the lowest voltage value panel in the system. The panel you proposed is so close in value to the one you already have (assuming it is still producing as it should be) that you wont notice so much power loss. It is about 15W of total power which at the end of the day between cloud cover and other factors you probably would not notice. But to be honest for a few more dollars just getting a 385W panel may work better for you.

Your main interests for quick calculations on panel power is VOC and rated amps.

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iostrym Alexandra ♦ commented · Mar 28, 2020 at 12:34 PM

thanks. I don't have yet my new solar panel. but I already have the victron smart solar. to be honest instead of the luxor panel I'm looking for maybe add a bluesolar panel from victron. (360wc but with quite a different Vmp : Voc=47.4V / Vmp = 38.4V) but keeping also my old pannel. except if new panel + old panel provided lower power than only the new panel.

FYI my current solar panel has Vmp = 35.8 V

"What you may find is the older panel has degraded and that it will dissipate power from the new one and bring the yield down." => in which case ? parallel or serial connection ?

"the system will track the power point of the lowest voltage value panel in the system. " => why ? I would have said that mppt algorithm will look for maximum power ? or does it mean that algorithm will track power beginning from lower voltage and then when a maximum power is reached it will stop even if at highest voltage there is another better Vmp value.

"Your main interests for quick calculations on panel power is VOC and rated amps" => Why Voc is more important than Vmp ? isn't Vmp a better indication ? or do you mean that if Voc match, often Vmp match also ?

What do you mean by "rated amps" ?

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