I just put my system online dec. 21 and I don't think it's max power is close to where it should be. My system consists of 36 evergreen 190s and an Sunny Boy 7000u inverter, this puts the power output rating at 6840 watts. So far the maximum output has been about 4kw with a max daily output of about 15kwh. The roof faces about 15 degrees east of south, and has a 3/12 pitch with about 4 - 5 hours of unobstructed sunlight at this time of year. I expected about 5kw peak output at this time of year. Am I expecting too much?

I suspect your system is working fine. The nameplate power rating for the panels probably assumes "STC" environmental conditions, which are somewhat idealized. In addition, you will have wiring and inverter conversion losses that are unavoidable (and also vary depending on lots of factors including DC MPPT voltage and current). Plus this time of the year your tilt/orientation losses will be really bad.

If you want a second opinion, google for "pvwatts", a simple NREL online PV calculator that will allow you to specify your location and system characteristics, and then produce an estimate of what you might expect for average power production.

Kirk Bailey

a 3/12 pitch is very flat .. about 22 degrees. Being in the Northeast, the Sun this time of year is closer to 62deg

( the 62 number is what the panels need to be tilted to so they are perpendicular to the sun which at its maximum is @ 28 degrees off the horizon )

http://solardat.uoregon.edu/SunChartProgram.html

using the above link, put in your zipcode, created the chart and you will have a 365 day graph showing where the sun arcs for your location. ONLY when the sun equals your roofs pitch can you expect STC power ( and if tempature is cool )

Your results (ratio of calc to actual) are similar to my newly installed system (27 Sunpower 205BLK panels, Sunpower/Xantrex SPR5000 inverter). Roof pitch for me is about the same as you, my orientation is about 250deg.

My system is theoretically capable of about 5000 AC Watts, however the typical daily max output is about 3400 watts (or less). I have seen as high as 4800 for short periods on a cold day with some clouds to reflect the sun.

I think your system is working normally, based on your peak output. the 15kw-h/day seems a bit low but this could still be normal for your location - for comparison, my daily output this month on a clear day has been typically 17.5 - 18.5 kw-h, with the 17.5 value being more common.

On a similar note, my friends new system (21 Sunpower 205BLK, Sunpower/Xantrex SPR4000 inverter) consistently outputs 90+% of my output, despite having far fewer panels. His roof has a steeper pitch and better south facing orientation, which really makes a difference.

One thing I did to help my peace of mind was to invest in a DC amp probe, this way I was able to verify that all 3 strings were working at the same level. I was certain that I had a problem due to my "low" output, but all the strings are performing the same, which is some insurance that the equipment is functioning OK. You may want to do the same for some independant verification of your system performance.

MrAMSOIL,
all of the statements made about your system are true. guppy gives a figure of 22 degrees and that would be the highest in the sky the sun would get to at noon time during the winter solstice if i read him rightly. you are doing this at 11am and that could make it moreso closer to the horizon. roughly by my math that means the pvs should be 90-22=68 degrees off of the horizontal minimumly with a comparrison of 90 degrees representing the pvs being straight up and down looking at the horizon. the angle you have is good for the summer solstice so at the peak of summer you should see plenty of pv power and all other timeperiods at less than optimal without allowing for different angles of optimization. the best overall compromise angle imho is what the lattitude one is at, but some that are the lattitude +15 degrees are also recommended thusly making your 22 degree elevation angle far off.
do understand we are talking of elevation angles for the pvs and the 15 degrees off to the east that you have them aimed will also compromise the output slightly comparred to one aimed due south.

PS Happy New Year all.

Happy New Year everybody and thanks for your quick replies. The reason I use 11am is because that's when the array is aligned with the sun. From what I get from the responses, my tilt angle is the limiting factor in my output. I guess I'll have to wait until the summer to get a better idea of what my system can put out.
Does anybody have any experience with the SunnyBeam remote monitor? The PC software doesn't save my data to a file the way it's supposed to.
Thanks again