So I’m wanting to run 11-430w sun power panels with tigo in series to a eg4 18k mppt port. Its going from panels on the roof—>junction box on roof—>attic—> inside garage(inverter location).im trying to find out 2 things: if what im wanting to do is correct setup. And if so, can I run a straight line using pv wire and ground from panel/rack through junction into flex conduit(in attic) then down into trough for inverter? If this isn’t correct, could someone please explain what I’m not doing correct or if there is a more efficient way. I have no trees or anything to worry about shading so I wanted to run straight dc to inverter.
Wire from panel to inverter?
- Thread starter Bricktop
- Start date
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Could you post the spec sheet of the panels?
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
The Voc is 51.2 volts if you put all 11 in series. STD Voc for the string would be 563.2V. That is still below the 600V limit for the 18Kpv, but the array would normally run above the 500V top end of the MPPT operation. In this range, the system would not be using the PV efficiently.
Furthermore, if it gets cold the panels could creep above 600V and damage the unit.
So... I would split the panels into two strings one of 5 panels and one of 6 panels. Unfortunately, that means running two sets of wires plus the ground.
For rating the wire, the code calls for using a value of 1.56 x Isc. For these panels that comes to 17A. The good news for you is that you will probably be running 10AWG wire and even after the derating it should handle 17A.
Furthermore, if it gets cold the panels could creep above 600V and damage the unit.
So... I would split the panels into two strings one of 5 panels and one of 6 panels. Unfortunately, that means running two sets of wires plus the ground.
Tigo RSD receivers or Tigo optimizers?
That sounds fine. However, you need to run two pairs plus ground. That means there will be more than 3 current carrying conductors in the conduit so the wire needs to be derated.
For rating the wire, the code calls for using a value of 1.56 x Isc. For these panels that comes to 17A. The good news for you is that you will probably be running 10AWG wire and even after the derating it should handle 17A.
Thank you for the reply. Its the tigo RSD. I was actually planning on two 11 panel arrays. But figured I’d concentrate on doing only one at a time. Plus they are at opposite ends of the house with the inverter basically in the middle. I came to the number of 11 because it was below the 600v limit for mppt on 18k. So would recommend staying below 500v? Or setup a different plan for wiring?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Correct. The unit won't be damaged between 500 and 600, but the mppt will be increasingly less able to harvest energy as the voltage approaches 600V.
In addition, you need to leave room for cold weather voltage rise.
Adjusting Solar Panel Voc for temperature
When designing you solar panel system, it is important to adjust you solar panel Voc for temperature in order to ensure you do not over-voltage the PV inputs of your solar charge controller. This paper shows how to calculate the Temperature...
diysolarforum.com
The nice thing about the 600V is that you don't have to keep the voltage under 500v in extreme cold. Say the temp gets to -20 once every 10 years but typically does not get below -10. You can design the system for -10, but still be safe in that rare -20 event.
