Hello all,


It has been a while. I was able to get Xantrex to help me with a new ST for my old ST, thanks much to Smitty Ovitt (new ST is not here yet). I have read the posts about array configurations and now question mine. I started with 20 Photowatt 105's set in pairs each set to 24 volts, paired again after the combiner into 5 matched pairs into the inverter. I added 6 more Photowatt 105's late last year. I now have 26 Photowatt 105's. I currently have 18 in pairs, and 2 sets of 4. The two sets of 4 (each panel set for 12 VDC) are each on there owne single ST input, the 18 pairs (each panel set for 24 VDC) are tied 3 pair to a ST input (this after the fuses in my combiner box). Is there a better configuration? I have these panels at basicly 0 angle or flat, my best day is 12KW and the best instant watt displayed on the old ST meter is about 1600 watts. I am not sure it matters with the ST but I thought you would be THE MAN to ask.

Regards,

Dave Friedeck

So you have 2600 watts STC facing striaight up ?? what lattitude are you at ??

Your array configurations sound fine ...

unless you live at the equator , you going to lose kWr's to being off angle from the sun ....

Thanks, for the reply. As for the latitude 34.0289, and yes and no as to giving up KW due to angle. First I have a limited amount of SQ feet to work with. Most of my sloped roof is from East/West and would not work well to get tilted to the south. The flat roof gets the max panel area when all are flat, if tilted there are two issues, shadow lines adding more space between panels (read less panels) and major wind issues (read wing). There is also an aesthetic issue, flat they cannot be seen from the ground. According to the PV Watts calculator I give up 12% to a fixed system at 30 degree tilt, I wouls loose 20% of my panels if tilted so flat is what they are.

Regards,

Dave Friedeck

Did you use version #1 or #2 of PVwatts ?

In the winter your going to be off by almost 60 degrees on the panel angle and have a 50% hit in possible power output ... that's pretty stiff but I also understand you have to make it work for your installation

A east or west install is typically much smaller hit in performance , my system is 30 degrees off of south (to the west) and my losses are not even measurable.

On thing to consider is your local weather , your peak performance is the summer due to the longer days and less angle error , but if your in a rainy climate (like Florida or GA) , this will reduce your summer yeilds and largely skew the overall yearly performance downard towards the 50% winter performace ... Food for thought

Henry,

The regon is Southern California, summer is dry and normaly clear. And yes the error is less in summer. Winter is wet by comparison and more grey days but when clear cool so good for making power. The roof area used was the only option at the time (other roof was wood shake). I was also able to ZERO my electric bill for the past two years with the current system and ST 2500, this year I will be under $100 but not Zero. The cause was very poor winter weather for solar power, lots of grey days. I look forward to the improved performance under these grey conditions. I have been selected as an SCE test site, one of 22, for them to look at system performance for owner installed, contractor installed, as well as region (costal, valley, desert). I am by the way using TOU / NET Metering to pull this off with just 2600 watts of solar.

Regards,

Dave Friedeck