Alternative Technology Assn Forums

1. 

   karmacoma
   Member

   I've moved to a new house and taken the grid-connected PV system with me, and on the new roof I am better off to add two new panels and make 2 banks of 4 panels rather than the old house's 6 panels in-line. Also it will bring the power closer to the design capacity of the inverter. Well, that's if I can find two 165W panels to match the existing panels (in terms of both power and panel dimensions).

   Problem is, I don't seem to be able to find Suntech STP165S 24V panels, like the other ones I have, any more. I do see that one retailer is selling Suntech STP175S 24V panels, but $1024 apiece seems high. Am I right about that, that is a high price? Also, the SMA inverter operation/installation manual does say to try match the power of all panels the same. But maybe 175W vs 165W is a minor difference that isn't going to cause problems? Or not?

   Of course instead of buying two extra panels I could just go with what I already have and do two banks of three panels, but I'd hoped to just go that bit extra. Love some advice here.

   Posted Friday 25 May 2012 @ 11:14:26 pm from IP #
2. 

   Lance
   Key Master

   That is indeed a high price, PVs can be had for close to $1 per watt if you look around, you shouldn't pay more than $3 a watt really...

   Posted Saturday 26 May 2012 @ 6:02:57 am from IP #
3. 

   karmacoma
   Member

   Thanks Lance. Yes I could get the current version of a Suntech panel, 190W output (STP190S-24) for $341.

   The problem is this (or maybe its not a problem? - this is where I need good advice):
   If I buy and connect two of these 190W panels in series to a string of six existing 165W panels, what will happen? Will I just effectively downgrade the output of the 190W panels to the output current of the 165W panels? I could live with that. Or will it create nasty effects that stuff up the system. What will happen? That's what I want to know.

   I wanted to stick with Suntech same as my existing panels and the physical panel dimensions are the same, so that makes it easier and neater to join on another two.

   Posted Monday 28 May 2012 @ 2:04:19 am from IP #
4. 

   ghostgum
   Member

   Without looking at the specs of the two panels, the likely effect will be as you describe: the 165W panels will restrict the current through the 190W panel, so the 190W panel will give you closer to 165W output.

   You would need to look at the I-V curves of the two panels to work out what would happen.

   Posted Monday 28 May 2012 @ 2:42:16 am from IP #
5. 

   Lance
   Key Master

   Yep, the 190 watter will just have a reduced output and may run at a slightly higher voltage than the 165 watters, but nothing that should cause any issues...

   Posted Monday 28 May 2012 @ 4:26:37 am from IP #
6. 

   karmacoma
   Member

   Thanks guys for your advice! Great to have that nagging question answered.

   Posted Monday 28 May 2012 @ 12:15:16 pm from IP #

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