I currently have two sets of PV panels; one a bank of 4 Unisolar 64s, and the other a bank of 8 BP 75s. I bought the Unisolars because of their advertised partial shading performance. I bought the BPs because I got a good deal on them. I'm considering adding substantially more panels but would like recommendations on what would be best for the 9 months of continual cloudy weather we get here in Western Washington State. [img]images/smiles/icon_confused.gif[/img]

You didn't mention if this is off-grid or grid tie ??.

First point , mixing panel type on the same invert (if a mppt based inverter) is going to cause problems. The mppt search will find the spot between the two different panels type , and the differnance is pretty big. crystalline and thin-film are very different in there operating parameters so in general this is a no-no.

If your using seperate charge controllers , that OK.

So is this gridtie or offgrid ??

Agree with Mssr. Guppy that the application is key and that you should NOT mix panels on an MPPT inverter. Another option is to use multiple inverters dedicated to each type of panel -- amorphous or polycrystalline.

Hi RandyR,

It is not a good idea to mix types of panels on the same charge controller but it is OK usually to have more than one controller on a battery bank.

My suggestion is to get panels at the best $/watt that you can find since you are more limited in sunlight than some of us.

If you can find it, compare specs of different panels at 10% sun to see how their output degrades. I have one panel that is spec'ed to only put out 5% of full power at 10%sun while most of the rest of my panels put out 9% or better at 10% sun.

Also, if you are mixing brands, try to get panels within .2V of each other at the max power point. e.g. the Photowatt PW-7500 is available with 75, 80W and 90W outputs. The 80W version has the closest voltage to my old Solavolt SV8500 85.5W panels.