Recommended Solar Panels

[markrw]

I would like to install some solar panels for my 24V system. 30 ~ 80 VDC. 40A. 1300W.

Can anyone recommend best brands for solar panels. Also can anyone comment on their experience with mono vs poly. I have read conflicting reviews and was wondering if anyone had some experience.

 

[RonSwanson]

I would like to install some solar panels for my 24V system. 30 ~ 80 VDC. 40A. 1300W.

Can anyone recommend best brands for solar panels. Also can anyone comment on their experience with mono vs poly. I have read conflicting reviews and was wondering if anyone had some experience.

That's going to be a little difficult to get near to the full capacity, because the voltage and amperage specs seem to favour the older 280-320W panels. I'd suggest looking around for them secondhand.
The mono vs poly debate has also subsided due to newer and better tech, but may still be a factor in older panels, where monos supposedly perform better under cloudy conditions. TBH it's the least of your worries.

 

[markrw]

That's going to be a little difficult to get near to the full capacity, because the voltage and amperage specs seem to favour the older 280-320W panels. I'd suggest looking around for them secondhand.
The mono vs poly debate has also subsided due to newer and better tech, but may still be a factor in older panels, where monos supposedly perform better under cloudy conditions. TBH it's the least of your worries.

I have found a lot of places selling the 300-330W panels.
I figured my best option was 4x320W panels connected in parallel

 

[RonSwanson]

I have found a lot of places selling the 300-330W panels.
I figured my best option was 4x320W panels connected in parallel

OK.
You mean two parallel, and two series. Look at the spec sheet's Voc and Isc, don't exceed it.

 

[markrw]

OK.
You mean two parallel, and two series. Look at the spec sheet's Voc and Isc, don't exceed it.

Couldn't I do all in parallel?

The voltage of the panels seem to be 30 to 37 and they are around 8 amps so that would keep me in the amp and voltage range?

 

[Mike Hoxbig]

Couldn't I do all in parallel?

The voltage of the panels seem to be 30 to 37 and they are around 8 amps so that would keep me in the amp and voltage range?

Parallel: add the current, voltage remains the same.
Series: add the voltage, current remains the same.

The reason why you need to wire in series is that the inverter requires a minimum voltage to operate...

 

[markrw]

Parallel: add the current, voltage remains the same.
Series: add the voltage, current remains the same.

The reason why you need to wire in series is that the inverter requires a minimum voltage to operate...

But if I bought something like this

Deserv Series 310W Solar Panel

Electrical Characteristics: Rated Power, Pmax(Wp): 310 Max Power Voltage(Vmp), V: 36.86 Max Power Current(Imp),A: 8.42 Open Circuit Voltage, Voc(V): 46.08 Short Circuit Current, Isc(A): 8.76 Module Efficiency(%): 16.00 Operating Conditions: Ambient Temperature: -40 to +85 degrees celsius Hail...

solarequipment.co.za

Where the voltage is up to 36.86 wouldn't that be sufficient? Or could the voltage still drop to below 30v on those?

 

[RonSwanson]

Couldn't I do all in parallel?

The voltage of the panels seem to be 30 to 37 and they are around 8 amps so that would keep me in the amp and voltage range?

You need to kickstart the charger, it should have a range specified. Higher voltage means that you start electrickery production earlier in the day. A higher voltage is also usually better because:

• Less voltage drop (DC is particularly susceptible to this); and
• Cable thicknesses (the more thickness the more expensive)
  • 8-16A can run on thinner cable than 32A

 

[RonSwanson]

But if I bought something like this

Deserv Series 310W Solar Panel

Electrical Characteristics: Rated Power, Pmax(Wp): 310 Max Power Voltage(Vmp), V: 36.86 Max Power Current(Imp),A: 8.42 Open Circuit Voltage, Voc(V): 46.08 Short Circuit Current, Isc(A): 8.76 Module Efficiency(%): 16.00 Operating Conditions: Ambient Temperature: -40 to +85 degrees celsius Hail...

solarequipment.co.za

Where the voltage is up to 36.86 wouldn't that be sufficient? Or could the voltage still drop to below 30v on those?

Not a good choice. Voc is 46.08, so if you put two in series (620W at 92.16V) it will blow your charge controller.
Look for a panel whose Voc gets you closest to 80VDC (your controller's max), in series.

 

[markrw]

Not a good choice. Voc is 46.08, so if you put two in series (620W at 92.16V) it will blow your charge controller.
Look for a panel whose Voc gets you closest to 80VDC (your controller's max), in series.

My inverter is a rentech 3kva axpert.

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

www.powerprovider.co.za

The one spec i forgot to include was that the max open circuit voltage is 102vdc.
So with those panels I linked I would be a little under the allowable open circuit voltage and the vmp would be 73.72 which is under the 80vdc max.
So would I be able to connect 2 of those panels in series safely?

Or would i be better off going for panels in parallel with a higher vmp like these.

Canadian Solar 420W Super High Power Poly PERC HiKU

Rating: 410W Efficiency: 18.6% Width: 1,048mm Height: 2,108mm Price per Watt: (R5,038/Wp) HiKU Super High Power Poly PERC module Super High Efficiency Poly PERC Module (CS3W-390-395-400-405P) With proprietary poly wafer and cell technologies Canadian Solar have developed an extraordinary...

pvstore.co.za

I could connect 3 of these in parallel. I know the wiring would be more expensive but I actually already have 6mm cables from my previous 12v setup and higher fuses so that is not a concern.

 

[TheChamp]

My inverter is a rentech 3kva axpert.

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

www.powerprovider.co.za

The one spec i forgot to include was that the max open circuit voltage is 102vdc.
So with those panels I linked I would be a little under the allowable open circuit voltage and the vmp would be 73.72 which is under the 80vdc max.
So would I be able to connect 2 of those panels in series safely?

Or would i be better off going for panels in parallel with a higher vmp like these.

Canadian Solar 420W Super High Power Poly PERC HiKU

Rating: 410W Efficiency: 18.6% Width: 1,048mm Height: 2,108mm Price per Watt: (R5,038/Wp) HiKU Super High Power Poly PERC module Super High Efficiency Poly PERC Module (CS3W-390-395-400-405P) With proprietary poly wafer and cell technologies Canadian Solar have developed an extraordinary...

pvstore.co.za

I could connect 3 of these in parallel. I know the wiring would be more expensive but I actually already have 6mm cables from my previous 12v setup and higher fuses so that is not a concern.

You are fine with the first ones, in series and connect them in parallel pairs to below the max power of 2400W.

 

[RonSwanson]

My inverter is a rentech 3kva axpert.

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

MCE Axpert MKS 3kW 24V Pure Sine Wave Inverter

www.powerprovider.co.za

The one spec i forgot to include was that the max open circuit voltage is 102vdc.
So with those panels I linked I would be a little under the allowable open circuit voltage and the vmp would be 73.72 which is under the 80vdc max.
So would I be able to connect 2 of those panels in series safely?

Or would i be better off going for panels in parallel with a higher vmp like these.

Canadian Solar 420W Super High Power Poly PERC HiKU

Rating: 410W Efficiency: 18.6% Width: 1,048mm Height: 2,108mm Price per Watt: (R5,038/Wp) HiKU Super High Power Poly PERC module Super High Efficiency Poly PERC Module (CS3W-390-395-400-405P) With proprietary poly wafer and cell technologies Canadian Solar have developed an extraordinary...

pvstore.co.za

I could connect 3 of these in parallel. I know the wiring would be more expensive but I actually already have 6mm cables from my previous 12v setup and higher fuses so that is not a concern.

Yes, that will work then. Wire 4 of them in 2 series, 2 parallel, will give you 1240W, (73.72V @ 16.84 A):



Always size the max voltage at VoC, remember that the specs are usually given at STC which is 25 degrees, and temperature drop will increase voltage.

 

[markrw]

Yes, that will work then. Wire 4 of them in 2 series, 2 parallel, will give you 1240W, (73.72V @ 16.84 A):

View attachment 1282748

Always size the max voltage at VoC, remember that the specs are usually given at STC which is 25 degrees, and temperature drop will increase voltage.

Ok that's great. Thanks so much for your help. I really appreciate it.
My previous setup was just a 12v system with a pwm charger so it was much simpler. Connect 18v panels in parallel up to the max watts. Mppt with series and parallel and Min and Max voltages can make things more complicated.

So is highest voltage with lowest amp always preferable from an efficiency point of view ignoring the cost of the cabling?

Then should I just run it as one single string down? I already have two strings going down to a combiner box from my previous setup so I could send each series string down separately or I could parallel it and send down as one string. Is there pros and cons for each both as efficiency and safety point of view?

 

[TheChamp]

Ok that's great. Thanks so much for your help. I really appreciate it.
My previous setup was just a 12v system with a pwm charger so it was much simpler. Connect 18v panels in parallel up to the max watts. Mppt with series and parallel and Min and Max voltages can make things more complicated.

So is highest voltage with lowest amp always preferable from an efficiency point of view ignoring the cost of the cabling?

Then should I just run it as one single string down? I already have two strings going down to a combiner box from my previous setup so I could send each series string down separately or I could parallel it and send down as one string. Is there pros and cons for each both as efficiency and safety point of view?

Run it as separate strings to a combiner box with fuses and an isolator. It is much easier for troubleshooting purposes, if you run it down as a single string and one string goes faulty you won't immediately know which it is, and isolating one string becomes easier while working. If it's all combined into one from the roof all your solar must go down to do repairs.

 

[markrw]

That's very true.Thanks again.
I currently have 25A fuses for my previous setup so I will just replace with smaller ones. Then it has an SPD and isolator.
Do I need to do any inline fusing between the panels? From what I understand is with connecting in series I don't need to?

 

[thehuman]

That's very true.Thanks again.
I currently have 25A fuses for my previous setup so I will just replace with smaller ones. Then it has an SPD and isolator.
Do I need to do any inline fusing between the panels? From what I understand is with connecting in series I don't need to?

Will need +- 10a fuse between ea string of 2 pannels maybe 15a

 

[markrw]

Will need +- 10a fuse between ea string of 2 pannels maybe 15a

Ok thanks. Do I put it on the positive where it connects to the other panel negative?

 

[thehuman]

Ok thanks. Do I put it on the positive where it connects to the other panel negative?

Sorry for my phone finger drawings , purplee blobs fuses

I would run ea string +- to near inverter and fuse ea end with a fuse
You get combiner boxes for this purpose, not hard to make your own tho

Can see internals in link

Takealot

 

[markrw]

Yes, that will work then. Wire 4 of them in 2 series, 2 parallel, will give you 1240W, (73.72V @ 16.84 A):

View attachment 1282748

Always size the max voltage at VoC, remember that the specs are usually given at STC which is 25 degrees, and temperature drop will increase voltage.

The 330w panels seem to be easier to get an than 320w. I assume being 10w over the 1300w max isn't an issue since I would never produce the max of the panels and the max amp is 8.78 so with 4 panels I would be under the max of 40A of my inverter.

 

[Koosvanwyk]

The 330w panels seem to be easier to get an than 320w. I assume being 10w over the 1300w max isn't an issue since I would never produce the max of the panels and the max amp is 8.78 so with 4 panels I would be under the max of 40A of my inverter.

You can produce more than the max of the panel

The panel will have a temperature coefficients (TCs), most often in terms of a percentage per degree Celsius (something like TC Voc = -0.35%/°C). This means that for every degree change in temperature of the panel, the Voc will change in the opposite direction by 0.35%. The Voc is normally measures and quoted at a panel temperature of 25 celsius. Therefore if there is a cold wind blowing, by example, but there are lots of sun, you can and will get a higher PV voltage than the quoted values