Hi,

I'm curious as to how this performance matches up with others...

The system consists of (24) 158 Kyocera panels and (4) Shell/Siemens SR-100 panels. One inverter has 1900 watts of PV while the other has 2300 watts of PV.

So far, sunny days have been few and far between, but there was (1) day this week in which it was mostly sunny, most of the day. For that day, the total AC kW produced was a little over 22kW.

The panels are mounted on the ground and tilted at a 40 degree angle. I am near La Crosse, WI which has a latitude of 43.5 degrees.

Thoughts?

Thanks!

~Alan~

what amperage of Kyocera's?
what amperage Shell/Siemens?
are the strings mix & match?
Do you have the 4 Shell's with 12 of the Kyocera's?
amperage of string is limited to lowest amperage panel in string if i understand these things correctly.
I am getting about 7kwh/day from a 1.1kw array in Rockville md

The Kyocera's are in strings of three... 23.2V@6.82A
The Siemen's SR-100 are in a string of four...17.7V@5.6A

(1) STRX2500 has (12) Kyocera 158's: (4) strings of (3)

(1) STRX2500 has (12) Kyocera 148's: (4) strings of (3) + (4) SR-100's: (1) string of (4)

The strings are ~35' from the inverters, wired with #10 stranded.

As a follow-up to myself, I believe that those numbers can't be too far from the norm? During peak irradiance, I am seeing about a 74% to 75% conversion efficiency from rated panel output to actual AC/kWh output. (Air temperature in the 70's (F)). I'll be curious as to how much the efficiency goes up in the winter on those really cold days.

Hi AJ,

I'm glad to see that you are interested in "Benchmaking" the performance of your system.

My system has a custom build tracker system with both azimuth and altitude percision (+or - 2% on rotation and altitude) positioning. The altitude range is 10 to 85 degrees and rotation range is 180 degrees. I'm telling you this so that you can understand that I have 2 more degrees of freedom than fixed or seasonal adjusted systems.

Panels: 56 kc120 and 16 kc125 for a total of 8720 panel watts
Inverters: 4 strx2500upg and 1 strx1500upg

AC watts/hr: 6,300 ac watts/hr from 8:00 am to about 6:00 pm

AC watts/day: YTD peak: 72,321 watts/day
Range (5/4/04 - 5/26/04): 61,885 to 72,321 watts/day
(Output is a function of time in a day not sun position)

AC watts/hr to Panel watts/hr: 6300/8720 = 72.2%

Inverter diminishing returns:

As an inverter is loaded with pv strings, the incremental output of adding additional pv strings degrades. I found that the first four strings of 480 panel watts loaded incrementally the same - in my case approx. 350 AC watts/hr per pv string. Adding a fifth and sixth pv string - shows a significant incremental decline - 75 to 150 watts/hr for the fifth and sixth strings. Since I have 18 pv strings of 480 to 500 panel watts to play with - I've seen this over and over. This is not unigue to the ST inverters. (Please check it out on your system during the peak hour of the day.)

Inverter Loading:

ST2500: all have 4 pv string of 480 to 500 panel watts - 80% loading

ST1500: have 2 pv strings of 500 watts - 67% loading

AJ's Systems:

Looking good - even though you have a fixed system - it will not loose ac power output due to incorrect inverter loading.

System #1: 4 pv strings of 474 watts = 1896 panel watts
Inverter loading: 1896/2500 = 76%

System #2: 3 pv strings of 444 watts = 1332 panel watts
1 pv string of 400 watts = 400 panel watts
Total: 1732 panel watts
Inverter loading: 1732/2500 = 69%

AC watts/hr to panel watts/hr (at peak): 74%

Thanks for the feedback.

To clarify the second array:

System #2: 4 pv strings of 474 watts = 1896 panel watts
1 pv string of 400 watts = 400 panel watts
Total: 2296 panel watts
Inverter loading: 2296/2500 = 92%

The overall performance of the two arrays, less DC losses and AC conversion are within one percentage point of each other, so I am not seeing any real degradation with the additional loading.

It is amazing to see your numbers when both altitude and azimuth are tracked. Sounds like an awesome system.

Thanks,

Alan

Hi AJ,

I'm not sure how I missed the numbers on the 2nd system - you should make sure that the inverter is not clipping your ac power output during the peak solar hours. Although, you don't have many options to do anything about it.

Module tilt angle:

At 40 degrees, your tilt angle is too high for this time of the year to provide optimum power output. My latitude is 37 degrees - my solar tracker puts the altitude tilt angle at 15 degrees from about 11:00 am to 2:00 pm. I've done this experiment several times and you're losing 15 to 25% of your power output - that's an additional 3 to 5 kw/hr you should be producing per day.

You can check this out by placing a round straight stick or pipe in the ground at 1:00 pm and angle it so it's shadow falls directly on its top - then measure the angle relative to line normal to horizontal. This should be your summer tilt angle.

Since you are ground mounted, you might want to consider making it adjustable. Henry's (solar guppy) systems are of this type - see his pics.

Good to talk with you - Richard

I may eventually make the panels adjustable (seasonal tilt.) The 40-degree tilt produces the maximum annual # of kW's for a non-adjustable rack. This is based on 20 years of climatic data for the La Crosse, WI region.

Click here for PV Watts calculations: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/Wisconsin/La_Crosse.html

I also created an Excel spreadsheet based on insolation and climatic data for La Crosse and I came up with similar results. A tilt range of latitude to latitude-15 degrees produced the most kW's/annum. To be exact, 38 degrees was the most productive.

If I was to do a seasonal adjustment, this would increase the productivity by ~5%, netting a gain of 250kW. 250kW * .07 (utility rate) or about $17/year advantage. For $17 per year, I couldn't justify making them adjustable. I am always concerned about wind loading, but maybe I'm just a bit paranoid.

I may leave them up for a year with a fixed tilt and then make them adjustable. Of course, every year has different weather so it will be difficult to compare the two.

AJ's system will never hit the Inverters 2500 watt limit ... even with edge of cloud effect ...

My arrays are 2900 watts ... or 500 watts more and It's not an issue for me

Richard , your system IS very impressive , but also not a good gauge to what typical system performance seem by more conventional systems... yours is what the BEST that can be (cost/time no object ) ... with your two axis tracking and ground mounting , your systems will out perform others in the summer by easliy 30-40% , if not more

AJ's numbers seem right on ..

On the Inverter incremental loading , the Sunties Peak is efficiency is at 1400 watt , it only drops 1.5% from 1400 to 2500 watts , not that big of a deal and when compared to panel variances , not sure if its even measurable for Home Owner Joe SInce your running at peak power nearly all the time (your two axis tracking) , you can see the difference , for the rest of us poor slobs .. we only see peak for a few minutes , the bulk of the generation is lower power levels and minimal differences

My Old system was ground based and 4 season asdustable ... My current system is roof based and fixed. From a performance standpoint , my current system does lose due to the heat on the roof and not perfect aligment to the sun angle.

The loss in about 200 watts/array at solar noon ... Even with this loss, I'd recommend this route and adding an additional panel to make up the difference for the simplicity of roof mounting. The savings in racking alone pay for the panels !!

Solar Systems vary widely - panel mounting, locations, equipment.... etc. This makes it difficult for a solar owners to determine if performance of their system up to par.

For the semiconductor industry, I develop a "Benchmark" standard for wafer fab die yields (number of good IC circuits on a silicon wafer) - wafer fabs have problems getting die yield information from other companies to determining if their die yield are competitive. The benchmark was a great success with over 140 wafer fabs from around the world contributing.

For us solar owners, I'm proposing the following "Solar System Benchmark" matrix as a way to compare system performances.

"Benchmark" = (System's Output)/(Systems Opportunity)

where:
System Output = AC Watt/hr Generated
System Opportunity = pv Panel Watts x Official Hours of Daylight
Official Hours of Daylight = # hours between sunrise and sunset

For Richard's tracker system:

System Output = 72,321(YTD peak 5/29/04) to 61,885 (7 day low)
System Opportunity = 8720 panel watts x 14.25 hrs = 124,260 watt/hr
Official Hours of Daylight: 5:47 am to 8:22 pm = 14.25 hours

Richard's Benchmark Range = 58.2% (YTD peak) to 49.8% (7 day low)


For AJ's Fixed mount system:

System Output: 22,000 watt/hr (only data point provided)
System Opportunity: 4192 panel watts x 14.25 hrs = 59,736 watt/hr
Official hours = used my time zone of 14.25 hours

AJ's Benchmark = 22000/59736 = 36.8% (YTD peak??)

Let's see what your numbers look like and what you think of this matrix!