Matching panels to Inverters

[wpns]

There are a lot of inverters and panels out there, and I'm trying to nail down some details.

I have an SMA inverter and except for some fiddly little engineering details, I'm pretty happy with it, and open to using SMA for my expansion, so I'm looking at the Sunny Boy 7.7-US, which has three MPPT inputs rated for 600V peak, 270-480V MPP range, and 10A input current per MPPT (18A max short circuit).

I can fit two strings of 9 of the JA Solar JAM54S31 395W panels on my roof, which are rated Voc 36.98V, Vmp 30.84V, Imp of 12.81 A, and Isc 13.71A (at STP), which will give me a Voc of 332V, Vmp 277V, so that should work, but Imp is too high for the inverter input.

Can I tie both strings to the 3 MPPT inputs in parallel and use all (25.62A) of the panel current, or is the panel current too high to put one string on each input (and leave the other MPPT input empty)?

Does that make sense? Do I need to pick panels with an Imp less than 10A and have individual strings? Are there higher-voltage, lower-current panels that I should select?

Thanks!

 

[Kuma]

SMA has a great design tool that will answer those questions.. search Sunnydesignweb You could use a smaller inverter. Especially if your strings are different orientations. ie South and West. Oversizing, 120~160%..., is normal and even recommended. The SMA tool spec'd the 5.0kw inverter for 6.4kw, two strings, and it is well within the acceptable range.

btw- The current SMA inverters are discontinued, at least in the US, and some sizes such as the 5.0kw are impossible to find and their is no committed eta for the new model. Also, the new model has an IEEE spec that has not been approved in the US. Research if that is important or not given your location.

 

[wpns]

Sunnydesignweb

Found it, and already had an account, because Sunny Portal, so yay! Unfortunately, you were also correct about the lack of inverters, there are none available in the automatic or manual selections, no matter how widely I set my parameters. Does this mean that that 10A inverter input and the 12.81A panel output are just incompatible? I tried selecting Polystrings, but that's kinda the opposite of what I want to do. I want to hook one string up to multiple inputs to get under the MPPT input.

 

[Kuma]

I meant that some inverter models are difficult to purchase in the US. I just went to the sma tool and can see all the inverters. Not exactly sure what youre trying to achieve so dont want to mislead you.

 

[wpns]

I meant that some inverter models are difficult to purchase in the US. I just went to the sma tool and can see all the inverters. Not exactly sure what youre trying to achieve so dont want to mislead you.

I haven't even gotten to the purchasing stage, but when I pick a string inverter for grid tie, I only see four options. I must be doing something wrong, I'll let the sales guy sort it out.

 

[400bird]

There are a lot of inverters and panels out there, and I'm trying to nail down some details.

I have an SMA inverter and except for some fiddly little engineering details, I'm pretty happy with it, and open to using SMA for my expansion, so I'm looking at the Sunny Boy 7.7-US, which has three MPPT inputs rated for 600V peak, 270-480V MPP range, and 10A input current per MPPT (18A max short circuit).

I can fit two strings of 9 of the JA Solar JAM54S31 395W panels on my roof, which are rated Voc 36.98V, Vmp 30.84V, Imp of 12.81 A, and Isc 13.71A (at STP), which will give me a Voc of 332V, Vmp 277V, so that should work, but Imp is too high for the inverter input.

Can I tie both strings to the 3 MPPT inputs in parallel and use all (25.62A) of the panel current

No

or is the panel current too high to put one string on each input (and leave the other MPPT input empty)?

That's on the edge, 12 amps is still under your listed 18 amp max. You'll leave some production unharvested on good solar production days (anything over 10 amps would be lost)

Does that make sense? Do I need to pick panels with an Imp less than 10A and have individual strings?

I would

Are there higher-voltage, lower-current panels that I should select?

Many, most panels I've seen are below 10 amps ISC. I'd recommend choosing different panels.