SolarEdge string design

[hamel01]

Hey all!

New to the forum so i hope someone can help me out! I have been working on designing an system for our house and have settled on either the Enphase IQ with Micro-inverters or the SolarEdge 11kw single phase inverter with optimizers.

The Enphase design is pretty easy and I have no issues with that. My issue is coming in with the SolarEdge. Here is what I am planning.

2 Pole mount systems each with 12 Trina TallAX 400W panels. According to the specs I can string 12 of those together so basically each pole would be it's own string. I am planning to either use the P405 or the P505 Optimizers on each panel. According to SolarEdge I can have a minimum of 6 Optimizers or a max of 25 per string but not to exceed 6000W per string. The TallMAX panel has a PTC output of 375w per panel so each string would be 4,500W. My plan is to run about 40' from each pole to an combiner that will be mounted on the house giving me the option to add some roof panels in the future as our power needs increase. From the combiner I need to run about 100' to where the inverter will be located by our incoming power. My question is how do I size the wire for that DC run? My head says I need to add up the voltage on the string which is 12 panels * 41.1v or 493v since the string will be combined in parallel the voltage will stay the same but of course the wattage will increase. According to the inverter specs it's max input voltage is 480v but according to the optimizer sheets I am well below the wattage allowed.. So my first question is what spec do I follow? Total wattage or total input voltage? Unless I am missing something this seems to be conflicting. Tieing into that question how do I size my DC wiring from the combiner to the inverter? I assume I need to take the combined wattage of 9kw divided by the 493v to get 18.2amps for the install size of the system. Does that seem right?

Am i missing anything or just thinking about this too hard?

Thanks for any help that you can provide!

 

[Ampster]

The Enphase and SolarEdge systems are great. I have both. You are paying a premium for capabilities like rapid shut down that you probably don't need. Also with complexity comes more possible points of failure. I would also look at string inverters. You don't need optimizers or panel level inverters. Yes you are thinking about this too hard and are looking at the trees and not the forest. The big concepts are that Increasing wire size or voltage will reduce line loss. You have long distances so reducing line loss should be part of the decision process. There is also more line loss with DC that AC so that may affect inverter placement. I would think you would want a big string inverter or two medium ones that can take the highest DC voltage then worry about the details of string sizing, wire size and inverter placement once you find a good value in a simple string inverter. I know i did not answer your question but hopefully added some information and framework to make your decision process more optimal.

 

[hamel01]

My understanding is that I have to have rapid shut down and I was steered toward those 2 systems due to some shading that I will have on the array's. That said.. I am going to look into the Rapid Shut down requirement to get a solid answer on that as well as the string inverters to see what that would look like.

 

[Ampster]

If you have shading then Enphase and SolarEdge are your best bet. Rapid shutdown is a firefighter protection requirement for roof mounted arrays that usually does not apply to pole mount. Essentially it is built in to those systems so it does not matter. So back to the issue of line loss. The decision criteria for the Enphase combiners is the amperage of each branch and the Enphase site can give you guidance. I don't know the string combining strategies with Solaredge but their website can give you rough parameters. When planning to put conduit in the ground use oversize conduit for flexibility because conduit is cheap compared to the cost per foot of trenching and retrenching. You can always pull more pairs or bigger wire in large conduit. Just think of increased wire size as the solution to line loss in either scenerio.

 

[400bird]

The solar edge optimizers are DCDC converters and will hold the DC input to the inverter at optimal voltage. My system holds at roughly 300 volts on both the 8 panel and 12 panel strings.

Why are you looking at an 11k inverter with only 9.6k of panels? Conventional wisdom is to put more panel output than inverter.