Seperate strings with single MPP tracker inverters

SolarCity

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Arms

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• Feb 21, 2011

• #1

A pretty fundamental question I have here....

I was under the impression that the effects of shading could be negated slightly by using seperate strings, even on inverters with single MPP trackers. However, speaking to a rep earlier, he told me that seperating the strings would have zero effect and the seperate strings would only be of use on inverters with two MPP trackers.

This makes sense but it is not how I understood it previously.

Can anyone help clear this up?

 

edexlab

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Arms

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• Feb 22, 2011

• #2

Just re read this to be certain and I would agree with you, however the Rep partially right also

if you've a 16 module array on one string then any shaded area; reduces output of the whole array
series connected

split into 2 strings of 8 and if one string is shaded then; one string's as normal, one has reduced output ,
series/ parallel connected

this is due to the differing I,V curves for series /parallel strings and how the Mpp shifts when there's shading ,
multi string 2 x mpp trackers reduces the losses further and so is better with two strings

but with a string inverter, if there's temporary shade you're still better off using 2 strings
but any shading will always reduce the output
all you can do is minimise the losses

 

Last edited: Feb 22, 2011

dansk

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• Feb 22, 2011

• #3

I agree with edexlab - ive just done a single MPP, 15 panel, 3 string array due to masive chimney in the way. Because its split into 3, if there is any shade on 1 of the strings the other 2 will be working and its not the whole array thats out of action.

 

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Last edited: Feb 22, 2011

Markc

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• Feb 22, 2011

• #4

Rep wasn't trying to sell a twin MPP inverter by any chance?

I have to agree that if shading is going to be an issue then splitting over two or more strings is an advantage but I would always try to achieve this with a twin MPP inverter. I just feel its worth that little bit extra.

I do agree mind you that I was also under the impression splitting even on a single MPP was worth doing.

 

L

Liam Norman

• Aug 10, 2011

• #5

Hi fellas, new member here! I have a Solar PV installation company in Cardiff

I was also under the impression that splitting strings would be more efficient, but thinking about it - it does make more sense with twin MPP.

The question is - who supplies twin MPP inverters?

 

P

PV Martin

• Aug 10, 2011

• #6

Most inverter manufactures have a 2+ x MPPT option inverter but you will find that these are all up around the 4500/5000 range.

 

L

Liam Norman

• Aug 10, 2011

• #7

Thanks Martin, the system is below 4kW so I'll see if the client wants mini inverters or is happy to go with a 3.6 standard

 

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PV Martin

• Aug 10, 2011

• #8

Power-One Aurora PVI-3.0

look at the Power -one range, i have never used them but they have a twin MPPT version starting at 3kw

 

L

liquidity

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• Aug 10, 2011

• #9

Doesn't the SMA Sunny Boy 4000TL support two strings?

 

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PV Martin

• Aug 10, 2011

• #10

yes it does Liquidity, its just a bit big for the 3.6kWp system IMO. and about £300 more than the Aurora 3.6kWp version.

i suppose its all down to personal preference.