simple.life2
Member
It has been suggested that we can expand our 1.575kw system by 3 panels to 2kw by adding them to our North-West facing sunroom roof, which has a completely different angle to the pitch of the original house.
So we'd end up with 9 panels at say 40 degrees, and 3 panels at 20 degrees.
I thought we'd have to put tilt racking up to match it to the angle of the other panels but our supplier says that it will work fine.
Does anyone think this is a good/bad idea?
Paul Denton
Member
simple.life2
first of all the inverter must be able to cope with two different string inputs, one string has your exsiting 9 panels (assuming 9 x ~175W) connected to it, and another string for 3 new x (say) 175W panels.
For any inverter there is an optimum no of panels per string, so the 9 might be optimal for string 1 of the inverter as it is, and adding 3 new panels (say 3 x 175W) on another string might work ok , but may not be the optimal for your inverter.
As for the size of the inverter, you want to make sure it has a nominal rating of least 2.0kw, (~2.5 kw might be preferable) as you don't really want to run it on it's limit.
What type of inverter do you have?
Reagrds
Paul
simple.life2
Member
Our inverter is a Fronius IG30 outdoor which according the Fronius configurator will take 2 strings of 6 175w suntech panels. As we currently have 9 we thought we'd add 3 more, just changing the string configuration from 1 x 9 to 2 x 6.
That makes sense, but I am concerned that the 3 new ones will be at a different angle... Do you think it will affect performance?
(Thanks in advance for your thoughts) 
rsigmund
Member
There is a rule of thumb for panel tilt angles that goes like "latitude + 5" degress or something similar - This angle is meant to maximise you year round solar gain and is around 35 degrees for southern aust.
20 degress will maximise your solar gain in summer and decrease your gain in winter.
Your output will be lower - but it seems that offten is is more cost effective to add an extra panel than pay for tilt mounting...
If you really want to get into it: AS 4509.2-2002 Stand-alone power systems - System design guidelines has worked example if I remember corretely...
Hope this helps
Benny
Member
I can't imagine that such a small difference in pitch will affect anything simple.life. I think problems arise when panels are split across roofs facing 90 deg different directions, or when there is partial shading but just a 20deg difference in pitch will only cause a minimal difference in intensity of radiation on the panels and they should all be operating close to the max power point.
simple.life2
Member
Thanks for your input... If there will be only minimal difference to the operating efficiency, would you do it?
(My husband and I are keen to produce more power than we use (getting Solar HW tomorrow) so are considering the extra panels to achieve this goal.) We really wish we'd just got a 2kw system in the first place!
