Thoughts please on circuit design

[octopusman]

I will be mounting 12 panels on an outbuilding in the garden - this will be split into 2 strings of 6 panels each. I have purchased a 3.6kW single phase inverter. The inverter will be affixed to the house 50m away, using 6mm solar DC cable. I was wondering if you could review the circuit diagram/ specs in the attached image, and share any questions/ critique ahead of me purchasing the rest of the stated components. I am self taught and this is a home project for me so please be kind, thanks in advance!

Reference information
PV Panels model: Canadian Solar CS3L-380MS-MC4, datasheet here
Inverter mode: Solis SOL-3.6K-RHI-48ES-5G-DC, datasheet here

 

[binky]

Why have you got the combiner box? Completely unnecessary.

 

[octopusman]

Why have you got the combiner box? Completely unnecessary.

Hi binky, thanks for your speedy reply. So technically my 'combiner box' isn't combining as it is 2 in 2 out, it is more to host the protective devices shown on my diagram. Also I believe Solis recommend some kind of isolation/breaker between the panels and the inverter which presumably helps when the solar panels need isolating away to perform maintenance on the inverter. Online I had read that a combiner box 'provides overcurrent and overvoltage protection to enhance inverter protection and reliability'. Also for 'rapid shut down purposes in case of sudden fluctuations in the current'. Though I also see now mentions that for two string residential installations one isn't required. So I am a bit baffled why 1 or 2 strings systems are considered 'immune' from these issues.

 

[binky]

Hi binky, thanks for your speedy reply. So technically my 'combiner box' isn't combining as it is 2 in 2 out, it is more to host the protective devices shown on my diagram. Also I believe Solis recommend some kind of isolation/breaker between the panels and the inverter which presumably helps when the solar panels need isolating away to perform maintenance on the inverter. Online I had read that a combiner box 'provides overcurrent and overvoltage protection to enhance inverter protection and reliability'. Also for 'rapid shut down purposes in case of sudden fluctuations in the current'. Though I also see now mentions that for two string residential installations one isn't required. So I am a bit baffled why 1 or 2 strings systems are considered 'immune' from these issues.

It's all built into the inverter, don't waste your money and time. Fit a DC isolator by all means, it does make fault finding easier down the line. NB there's a lot of drivel on the internet, and a lot of the information is for different countries with different standards and out of date.

 

[octopusman]

It's all built into the inverter, don't waste your money and time. Fit a DC isolator by all means, it does make fault finding easier down the line. NB there's a lot of drivel on the internet, and a lot of the information is for different countries with different standards and out of date.

Good point there, thank you. How about the other components I have put in the circuit?

 

[binky]

Looks fine, but I wouldn't isolate the earths on the AC side. Keep those connected as it allows the capacitors in the inverter to discharge safely when turned off for maintenance

 

[octopusman]

Looks fine, but I wouldn't isolate the earths on the AC side. Keep those connected as it allows the capacitors in the inverter to discharge safely when turned off for maintenance

Brilliant, thank you

 

[stuboy]

I'd like to add to what Binky has said.... but err, I can't, he's got it covered.

Keep Solar on ;-)
Stu

 

[Bob Smith]

I see a DC breaker. I think there should be one on each string before entering the inverter.

Maybe if you have updated your diagram, post it again for another peer (Binky) review

 

[binky]

I see a DC breaker. I think there should be one on each string before entering the inverter.

Maybe if you have updated your diagram, post it again for another peer (Binky) review

Some isolators will take 2 strings, but I prefer one each, keeps it simple for future fault finding.

 

[Chrisbee]

My installer showed a string DC isolator on his diagram of my system, but the string cables plug straight into my inverter (Solis hybrid, 2 strings).
When queried, he says the isolator on his diagram is the one on the inverter it's self. Is this acceptable do you think?

 

[binky]

My installer showed a string DC isolator on his diagram of my system, but the string cables plug straight into my inverter (Solis hybrid, 2 strings).
When queried, he says the isolator on his diagram is the one on the inverter it's self. Is this acceptable do you think?

It is, I've done that many times.

 

[Chrisbee]

Thanks Binky. I'll add a note to the diagram to make it clearer.