2 inverters?

woko · Sep 13, 2011

Hi all. Just looking at a job where I going to fit 7 250w panels to one roof and 5 more to a lower roof.

Would you use two inverters for this? Or 2 strings on one inverter?

The reason I ask is im under the impression that the strings have to match if you use one inverter.

TIA

SolarCity · Sep 13, 2011

You are correct that the two strings have to match - they need to have the same amount of modules, be at the same pitch, orientation and to some extent, be subject to similar shading conditions. However, you can counter this by using an inverter with a dual MPP tracker. Or, as you say, you can use two inverters.

SpitfireW'sale · Sep 13, 2011

By connecting two unequal strings to the inverter (1 MPP Tracker), you are going to have two different Vmp and both strings are operating at loss. The MPP tracker is cable of finding the Pmax point of the system. Because of the fact that there are strings connected in parallel, each string's operating voltage MUST be identical. This means that either the tracker chooses the operating voltage of the 5-Modules string resulting in the increase of the current of the large string, or it keeps the operating voltage of the 7-Modules string forcing the small string and thus the modules to produce more current (based on I-V curve of the modules). In both cases, this unequal number of modules per string results in power losses of your system.

By using inverter with two MPP Trackers as BiggSolar mentioned before, you are able to connect two unbalanced strings to one inverter because each tracker is an indepentent circuit.

Unfortunately, the availability of such small single phase inverters with more than one MPP Trackers is small. Thus, you might need to have two small inverters of 1 MPP Tracker, unless the two roofs are identical: same inclination, same orientation and the distance is short, so you can split in two 2 strings of 6 Panels connected to one MPP Tracker inverter.

It's hoped that my answer helps you.

Kind Regards

SpitfireWholesale