Two string inverters vs one?

[ocdave]

If your two orientations have subarrays of equal size, without any partial shading of either of them during those hours when they would both be producing, then they could be put in parallel on one MPPT input. Xantrex and, I believe, SMA have published white papers on this subject based on both theory and experimental data.
I would look more closely at the geometry of your proposed installation to see whether you fit this scenario.

I don't have the details on the number of panels per string, but given that there are 3 different areas of the roof that the panels would be mounted to, I'm assuming that the subarrays would NOT be of equal size so an inverter single MPPT would not work. The good news is that the cost of two smaller inverters seems to be not that much more than the cost of a single larger inverter.

[inetdog]

I don't have the details on the number of panels per string, but given that there are 3 different areas of the roof that the panels would be mounted to, I'm assuming that the subarrays would NOT be of equal size so an inverter single MPPT would not work. The good news is that the cost of two smaller inverters seems to be not that much more than the cost of a single larger inverter.

Yeah, 3 does not go into 34 very evenly.
Now if you had two clusters of 10 and one of 14, you could get by with a total of two MPPT inputs. But with, say, an 8, 12, 14 division you would have to have three inputs.

[Naptown]

Yeah, 3 does not go into 34 very evenly.
Now if you had two clusters of 10 and one of 14, you could get by with a total of two MPPT inputs. But with, say, an 8, 12, 14 division you would have to have three inputs.

I will leave that alone
3 inputs?
A Howard Stern kind of thing

[silversaver]

So here is the answer I got back from the vendor on why 2 inverters are required...

Due to my system's size (8.3kW DC) and the fact that there are two orientations, two string inverters are required. The SMA 8000TL-1 only supports a single MPPT so it can't be used for my installation with 2 orientations.

They are right. For that size of solar system, you need at least 2 inverters on 2 roofs/directions.

Very good tool for SMA design tool:

http://www.sma-america.com/en_US/services/solar-design-tools.html

give it a try

[ocdave]

So here is the answer I got back from the vendor on why 2 inverters are required...

Due to my system's size (8.3kW DC) and the fact that there are two orientations, two string inverters are required. The SMA 8000TL-1 only supports a single MPPT so it can't be used for my installation with 2 orientations.

Just to close the loop, here are the two inverters that the vendor is quoting: SMA SB3000TL-US-22 and SMA5000TL-US-22

[david.solar]

we just signed our contract last week and are getting 2 SMA string inverters because we have two arrays, one with panels on the West (SW) the other with panels on the South (SE).

due to the different orientations, they use separate inverters so that the different arrays aren't affected by one another. as you may know, in a string array the loss of output of one panel affects the output of the entire array so you don't want that to affect the second array on another part of your roof if at all possible.

i guess the con is that you have to replace two inverters rather than one.. but then again, another pro of having two is that if you have one inverter failure, the whole system won't be down either.

Inverters these days (specifically Power One) have dual MPPT inputs. Meaning that you can plug in two separate arrays with two different orientations and they will be independent of each other. I would ask them to change the inverter bc having two inverters is much more expensive than just having one. I am an installer and we use Power One specifically for these situations with multiple orientations and they work great.

[bando]

Inverters these days (specifically Power One) have dual MPPT inputs. Meaning that you can plug in two separate arrays with two different orientations and they will be independent of each other. I would ask them to change the inverter bc having two inverters is much more expensive than just having one. I am an installer and we use Power One specifically for these situations with multiple orientations and they work great.

our system is almost 12 kW. we got a few quotes and even the one that uses Power One quoted two inverters PVI 5.0 i think. i guess it's a large system?

[david.solar]

our system is almost 12 kW. we got a few quotes and even the one that uses Power One quoted two inverters PVI 5.0 i think. i guess it's a large system?

Ahh, I see. You definitely need two inverters for that size. Congrats on your new system!

[Naptown]

our system is almost 12 kW. we got a few quotes and even the one that uses Power One quoted two inverters PVI 5.0 i think. i guess it's a large system?

that's because they dont make one that large

[DanS26]

To get back to the original OP question....I think two inverters is the best decision. With two inverters you will over time see a constant relationship between the outputs. Thus if a sudden change in that relationship occurs you can start the diagnostic procedures immediately. Potentially saving you lots of time, energy and money.