Hello,
I have been wondering in what way does Voc operate, is it always the same or does it depends on the suns intensity? Why im asking is because i have 2 panels 465 w connected in series on my ac200max. Voc on those panels is 50 V. If i want to put one more panel in series it will cross the limit
of 145 V .
Now i never get full benefit from my panels - in prime time i have around 800 w of solar power coming in - that is because of my orientation and near flat roof, i understand that. In winter on a sunny day i barely get 350-400 W. That is the reason i want to overpanel.
So if Voc is related to suns intensity then i should get away with 1 more panel in series.
Otherwise i must get 2 more panels and put it in series and connect it in paralel with my first 2 panels, but in that way im wasting a lot of solar because panels are 11 A , and 200max have 15A limit, and my setup would have 22A so im loosing around 7A x 84V(usable charge)= 588W .
So what do you think, can i get away with one more panel , or shoud i get 2 ?
Hi @krule2468,
Voc (Open Circuit Voltage) is the maximum voltage a solar panel can produce under ideal conditions, without any load connected. It’s crucial to know that Voc varies with temperature and sunlight intensity:
- Temperature: Voc typically increases in cold weather (by 10-15%).
- Sunlight Intensity: Voc is influenced by sunlight but not as dramatically as temperature affects it.
If your panels have a Voc of 50V each, three panels in series would give you a total Voc of 150V, which exceeds your AC200Max’s limit of 145V. This can potentially damage your system. The cold winter days could push this voltage even higher due to the temperature effect on Voc.
Regarding parallelism:
- Parallel identical strings: Ensure the same number of panels in each string, identical in type and facing similar shading conditions.
- Consider your shading: If shadows are significant during winter, over-paneling might not yield the expected benefits. Series setups tend to manage shading slightly better.
Parallelism is not easy to properly put in place, especially when trying to defeat long winter shadows. The risk of hot spots is higher (cell overheating due to uneven current flow in response to shadows). The global efficiency of the system is not guaranteed to increase when adding parallelism to your system.
Again not the awser im looking, if i never exceede 900W on my setup, im around 800W at most on ideal conditions, what would my Voc then be on my 2 panels-propably less then 100. Can i mesure that?
Besides the correct information that @Derceto told you, and apart of what mathematics and science said, which is absolutely to follow when you are building a high quality and professional system who follows standards, I think you also want to better understand how voltage is delivered to your Bluetti through the conductors and elements of your PV system.
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Other than VoC which specify the nominal maximum voltage from the panel, there are multiple factors that could contribute to a voltage drop to your end device, such as:
- cable length: a cable is a resistance which progressively lowers the voltage
- connector contacts: every contact cause the voltage to jump and that creates resistance which lower the voltage
- inefficiency of the panel: real values are always lower than advertised values due to efficiency
- temperature and sunlight intensity curve which are unlilkely to cross: a lower panel temperature at which VoC is maximum is unlikely to be reached while sunlight is at its maximum since it will increase the panel temperature
For the above reasons, with 3x 50 VoC panels in series, you will never reach 150 V at the PV input of your AC200MAX.
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Since we are here enjoying and learning and having fun while using our portable power stations, that will be useful for you to better understand how everything works, for instance you could carefully check the cable end voltages during full sunlight while using 3 panels in series and draw your own conclusions.
But, even if this answer will better fit you, that doesn’t mean you should rely on this theoretical conclusion for sizing your PV system as most of the time you will end up making mistakes.
Standards and specifications are there to allow us to size everything in the right way by only relying on values that fit every different configuration.
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With that being said, as already suggested, your safest option with your current panels which will follow the correct specification is: 2 panels in series. If you would like to increase the input power with the same panel type you would add 2 more panels in parallel in a 2S2P or 2S3P configuration that due to your panel orientation, during Winter, they will unlikely reach the full current, thus benefitting of more power.
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Alternatively, you should replace your panels to reach a VoC which will be more suitable for your device and add more series in parallel to maximize production during Winter.