I am looking at the Bluetti AC300 with the 150 volt input max. I like this solution because it is just plug and play. I don't like the foldable panels though from the same manufacturer. I get that 150 volts input capacity means you can use other panels in series up to 150 volts and they list max as 2400 watts. Does that mean I can buy 6 panels that are 24v 320watt, wire them in series and plug them into this system with the correct adapter since that is 144 volts and still under 2400 watts? Or is that getting a little close to the 150v for comfort? I know with my little 100 watt system the 12 volt panel actually brings in more than 12 volts and it occurs to me that if the same is true of all panels, 144 listed volts could be over 150 actual volts.
Need help understanding 150 volt max input
- Thread starter tedsc
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LithiumSolar
Solar Enthusiast
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You need to look at the Voc rating of the panels (open circuit voltage). A 24V panel will have a much higher open circuit voltage. Your string Voc cannot exceed 150V. Even then, you'll also want to consider that the panel's open-circuit voltage will be higher than the rating on the sticker in cold weather. So yes, even if the 144V you're calculating is the open-circuit voltage (which I doubt), it's still too close to 150V because of the low temperature concern 
For example, Renogy 24V 300W panels (random Google result) have a Voc of 38.80V so if you have 6 of them in series, that's 232Voc.
For example, Renogy 24V 300W panels (random Google result) have a Voc of 38.80V so if you have 6 of them in series, that's 232Voc.
Please note that 12V or 24V panels are neither. Unless you are trying to use a PWM solar charge controller you should ignore such references. Look at panels based on your needed wattage.
As mentioned, the panel's Voc is the important and only relevant value when determining how many panels can be put in series for a given MPPT solar charge controller.
Also note that Voc goes up in colder temperatures. Depending on the conditions you plan to use the panels you need the total Voc of the array to be 5%-20% lower than the max PV input voltage of the charge controller.
As mentioned, the panel's Voc is the important and only relevant value when determining how many panels can be put in series for a given MPPT solar charge controller.
Also note that Voc goes up in colder temperatures. Depending on the conditions you plan to use the panels you need the total Voc of the array to be 5%-20% lower than the max PV input voltage of the charge controller.
Thank you for the reply. Follow up question then, is there a reason not to add/remove a panel from the series array based on the season? My thought process is to buy more panels than needed as I have other out buildings I will also need panels for in the future, but build this array such that the combined Voc is 120 (3 panels each rated at 40 Voc). I want to put 4 panels on that roof however and just add the 4th panel to the array in warmer months.
Thanks
Thanks
OffGridInTheCity
Solar Wizard
You shouldn't have to add/remove panels - instead you can parallel them to keep the voltage down and still reach the max wattage the Charge Controller accepts. (or get a different Charge Controller with higher specs).
To try to illustrate the idea - Think of 2 strings of panels arranged as 75v @ 1200w *in parallel*. This would be 2400w total coming into the charge controller. Now think of 1 string of 150v panels @ 2400w which is 2400w. The power is the same in both examples but the 75v arrangement is within specs of the controller and the 150v is not (e.g. too close to 150v max to accommodate temp changes etc).
This is why controllers give BOTH a max voltage and max wattage specification - and then one can arrange panel layout to be within both specs.
OffGridInTheCity
Solar Wizard
Suggest some youtube'ing. Search series vs parallel and you'll get many good videos.
Here's a good/basic intro into panel wiring
The former is simpler and only requires one pair of Y connectors.
But the choice depends on the result you need. Is this for 6 panels? There’s a big difference in volts and amps between 3S2P and 3P2S.
Yes, the I have 6 panels on order at 320 watts 40 open volts each. So 3S2P sounds like the way to go. Do the OCPD fuses then go at the positive end of each series array? I am not clear on where best to put those? Also what size fuse for the OCPDs?
You don't need any fuses with a 3S2P setup. It's not until you get to 3P or more that you need to worry about fusing each string.
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