Combining PV strings

[SolarDude]

Can you combine two PV strings in a residental installation. I have a PowerOne inverter and 3 PV strings. PowerOne inverters have two MPPT's but only enough room to land 2 strings. So I want to combine 2 strings into one string then land the combined string and single string in the two MPPT's.

 

[jaggedben]

There's no reason you can't do this. Technically you are combining two strings into one input (not into one string).

If the short circuit currents of both strings are less than the ampacity of the conductors, you don't need a fuse. Otherwise you need a fuse.

 

[SolarDude]

Can I use a polaris block before I land the conductors in the inverter. The inverter only has enough room to land 4 wires 2 positive and 2 negative. I heard I had to use a listed combiner box since I am combining two strings.

 

[jaggedben]

You don't necessarily have to use a listed combiner to combine two strings. Again, if the ampacity of the conductors is adequate for both strings, you don't need a fuse. Usually we use #10 wire for PV strings and so you don't need a fuse for two strings with a current per string of less than 10 amps. Three strings or more and you generally will need a fusing, and fusing generally requires a listed combiner.

You could use a polaris connector, a Buchanan splice, or anything that is listed for connecting the conductors you're using. You could even use a wire nut, but just make sure you do it absolutely securely and won't have live DC wires coming loose.

 

[Zee]

Can you combine two PV strings in a residental installation. I have a PowerOne inverter and 3 PV strings. PowerOne inverters have two MPPT's but only enough room to land 2 strings. So I want to combine 2 strings into one string then land the combined string and single string in the two MPPT's.

as long as you don't expect independent mppt tracking of the 2 combined strings

 

[ggunn]

Can you combine two PV strings in a residental installation. I have a PowerOne inverter and 3 PV strings. PowerOne inverters have two MPPT's but only enough room to land 2 strings. So I want to combine 2 strings into one string then land the combined string and single string in the two MPPT's.

Yes, you can do that; in fact, you must do it to get all three strings into the inverter. Pick the two strings to combine which have the most similar environment WRT hours of sunlight, orientation, shading (if any), etc. to combine so that the MPPT will be most efficient. If all three strings have the same conditions, then paying for an inverter with dual MPPT might not be worth the investment.