My system is now up to 3400 watts! I'm generating about 14kwhr/day, way more than I use. My current system uses an array of 12 175W Sharps feeding a Sunnyboy 2500, and an array of 4 175W Sharps, 2 185W Sharps and 4 SX60's feeding an upgraded ST1500. The larger array faces about 150 degrees, and the smaller one faces about 240 degrees (yet oddly gets more hourse of equivalent total sun.)

The history behind this odd system:

In 2000, I cobbled together a 600 watt guerilla system based on the original ST1500 and four 150 watt Solec panels. It worked very poorly. Trace was no help and I gave up after a while.

Then I moved, and I decided to do it right. I found a contractor who would take care of all the paperwork, and I did the installation of the first system (a 1500 watt SunnyBoy system) under his guidance. It worked well and I quickly expanded that system to 2100 watts.

I was about to toss the ST1500 when I heard about the replacement program. Couldn't hurt to do that, so I sent it in and got a replacement six months later. I realized that I had a bunch of panels left over from other projects, and I could scrounge up two 48 volt strings. I installed the ST1500 in a temporary location (in the laundry room, plugging into the dryer outlet and a special DC outlet going up to the roof) and connected the panels. It worked well, and now I'm getting 8.5kwhr/day from the 2100 watt STC DC Sunnyboy system and 5.5kwhr/day from the 1300 watt ST1500 system.

Unfortunately I am now out of roof space, so it looks like I'll be stuck at 3400 watts.

And using your numbers , The XR-1500-UPG is out performing the Sunnyboy by 3% when comparing array size to delievered watts to the grid ....

Where is this system located?

I too hav wondered if there are any contractors out there that will basically only handle the paperwork? I want to do my install myself, but dealing with the solar rebate paperwork is a pain in the rear....

If you are in the bay area CA I would be VERY interested to find out who you wqere dealing with.

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Well:

1. The SMA array is facing around 150 degrees; the ST array is facing around 240 degrees. That would tend to favor the SMA.

2. Morning fog is very common, often until 10 or 11 am. That would tend to favor the ST.

It would be hard to really compare the two inverters unless I could rewire and switch the large array over to the ST. Even then it might not be a good comparison because the ST1500 might start to limit on a 2100 watt array (although if it _still_ outperformed the SMA you could definitely say it won in the efficiency category.)

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Coastal San Diego.

You say you have an "array of 4 175W Sharps, 2 185W Sharps and 4 SX60's feeding an upgraded ST1500". I'd be interested in discussing the mixing of panels with different operating parameters with the other guppies. The MPP of especially the SX60s and the Sharp panels may be different, with probably the ST1500 favoring the MPP of the Sharp panels, which vary in current contribution between the 175w and 185w flavors by about 5%. But since each Sharp flavor is its own string, it's all additive anyways. So, I'm wondering two things :

1) Is the SX60 possibly skewing array performance too much ? From the numbers I see, the answer is no, and I'd like to understand exactly why.

2) What would the effects be of wiring a 175w and 185w panel in series to form a 48v string ? The rule of thumb is usually exactly the same panel per string, but I don't see a big negative effect in implementing a string consisting of the same technology and manufacturer's panels. Why would anybody do this ? Because of availablity of newer panels or better price to facilitate a system upgrade with a similar though different one from the same manufacturer.

Thoughts ?

-- Larry H

Apparently most manufacturers consider a 10% plus or minus variation from specification to be normal. If this is true of the 175/185 watt panels, then a "175 watt" panel could be putting out 175+17.5=192.5 while a "185 watt" panel could be putting out 185-18.5=166.5. This really sounds ridiculous, so perhaps the difference between the panels is that the 185 watt units tested better than the 175 watt units.

Has anyone actually tested all the panels in an array? How much has anyone actually observed them to vary? If they really do vary significantly, then the best performance would seem to require matching of units within a string. Each string would be limited by the lowest performing panel.

That still leaves quesiton #1 unanswered. Concerning your question about manaufacturing variances, I recall reading an article either in HomePower mag or on the web in the last two years in which these two guys that happened to have a tilted rack on their property filled with several different manufacturers of panels found the variances from the same type of panel to be very minimal, and the degradation over time to be better than published. They had panels on their racks over twenty years old, and still going strong. If somebody else recalls that artical, lemme know (could even be Sandia Labs or NREL research).

Larry H