Out of interest. effect of East/West split on one string?

[Morgan keith]

I wouldn't do it but a client asked about an east/west split on one string. I couldn't quite describe how bad the effect would be? Would the 8 on the east side(shaded eg.) drag the current down from the 8 on the west (sun shining on)? Or any other answers? Much appreciated

 

[SolarCity]

Yes, the panels in the non-sunny area would bring the current down of the sunny area - very inefficient, and depressingly common.

 

[BruceB]

If the west and east strings have an identical number of panels and the two strings are put in parallel rather than in series, then according to Fronius the effect is not as bad as you might think. There is a paper on the subject on their site albeit I do not have the link to hand.

With the availability of twin mppt inverters I would not do it though.

 

[Earthstore]

I couldn't quite describe how bad the effect would be?

Tell him to drive his car for a week and see how many MPG's he gets, also ask him if it is slower too.

 

[Worcester]

To raise a thorny subject:
Interesting article here from SMA: Sunny Design: Polystring Configuration | SMA Inverted
and their paper here: http://www.smainverted.com/files/2012/12/Article_Polystring_East-West-Orientation-TEN122510.pdf
This came out of discussion for a large east / west commercial roof where SMA are promoting their STP-20000TLEE-10 Single string inverter
They key comments are good design, right size inverter, low losses (0.25%) even with a single string.
Food for thought

 

[Gavin A]

To raise a thorny subject:
Interesting article here from SMA: Sunny Design: Polystring Configuration | SMA Inverted
and their paper here: http://www.smainverted.com/files/2012/12/Article_Polystring_East-West-Orientation-TEN122510.pdf
This came out of discussion for a large east / west commercial roof where SMA are promoting their STP-20000TLEE-10 Single string inverter
They key comments are good design, right size inverter, low losses (0.25%) even with a single string.
Food for thought

you know why though I assume?

Because their tripower inverters aren't set up to allow for equal strings on the dual trackers, you can only have 1 string on input B vs 3-4 strings on input A.

for east west systems I'd spec power one every day of the week, as they allow for equal inputs on each side, and the 30kW inverters are priced better per watt than the SMA anyway, so SMA's argument only holds water if referring to SMA inverters only. It's still a bodge job way of doing things to make up for the inadequacies of their range, just as it was when Fronius were making the same argument IMO.

 

[Gavin A]

good to see their analysis of the best sizing of inverters for east west systems aligns with how we've been doing it / trying to do it for the last few years. Some customers won't have it though and insist on the full 3.68kW AC ouput dual tracker instead of the 3kW version that would actually get them a slightly higher output level overall.

 

[Worcester]

I realise SMA's reasons, however on some of our larger systems (100kW+) when the roofs are only at 5 - 8 degrees the costs savings and the offer of SMA's PPP output warranty (they'll pay for lost output if an inverter goes down), could outweigh the disadvantages of the single MPPT.

I've got them (SMA) working on a large project at the moment, we've already sized and designed it using twin tacker STP inverters and optimised sizing so have a good idea what the putput should be, it will be intersting to compare that with SMA's figures We've also designed it using Power-One Trio's so the comparisons will make interesting reading, could be a couole of weeks before we know the outcome so will post back here later.