I don't know what part of the country you live in, but using the default values from the Xantrex sizing calculator (record low = 14F, avg high temp = 95F), 3 strings of 9 panels (27 total) fits nicely within the calculator limits.


9 modules =

Max Voc at Min temp (Vdc) = 473.29

Min Vmp at Max temp (Vdc) = 304.6

I wouldn't rule out the SMA 5000US. It's in the same price at the GT 5.0, has almost 1% better efficiency and will nicely support your three strings of 8 (w/ room to grow). I've installed an east facing shed (iwthout the doors on) I got from OSH to house my Sunny Boy and it's been working just fine for years in there. So it does get some high sun protection but will always run warmer than the outside ambient. I did not want to use up space inside my workshop/garage for my solar electrics.

SMA has a sizing facility on their website:
http://www.sma-america.com/solar-techno ... ndex.html#

Seems to be relatively straightforward to use. I was able to size yours in a minute.

Seems that you guys are fixated on a fan, which the 5000US has. The unit has overheating protection in the rare case the fan does go. It's funny that some folks here have installed a fan on their GTs anyways. I'd like to hear from somebody who has had a fan go out on an SMA (probably post this question on the SMA board).

It looks like the communications on the 5000US is optional whereis integral on the GT 5.0 - that might be a real salient difference between the two inverters if this facility is highly desired without additional cost (I suspect most PV homeowners are just interested in turn-key and are not at the solar monkey stage we are at in feeling the need to constantly monitor).

BTW - the max temp on the GT 5.0 is 149F.

The SMA was also a consideration, but it is actually a fairly costly option to enable the web browse function. It does have great specs as you correctly state, though. And nice looking design. But I'm not sure about the 1% efficiency edge...aren't they both rated at 95.5% CEC?

Also, the Xantrex/Sunpower offers a wired monitor that they throw in for free.

I decided to do a 27-panel install, it is going on the roof next week and hopefully I will have utility approval to go online about a week later. I'll post some notes after it is up and running.

For the sake of the audience reading this, just how much was the communications options on the SMA unit? there's a few to choose. Appreciate it..

"BTW - the max temp on the GT 5.0 is 149F."

The max ambient temp on the GT series is 149F (Xantrex Manual pg 2-2).

The GT will shut down when the internal temp is greater than 176F, & will restart when the temp drops to less than 158F (Xantrex Manual pg 5-8).


http://www.xantrex.com/web/id/1890/docserve.asp

There is a wireless performance monitor, I seem to recall it was about $400, maybe a little less. To get the web monitor up required a couple of items, I think those added up to about $300.

None of this stuff is really necessary...but, since I am a tech freak I knew if I went with the 5000m I would wind up spending whatever to get these capabilities...that come free with the 5000x.

A fan (in it's current incarnation) is a mechanical device with moving parts & bearings. Bearings have a finite lifetime, and WILL fail. The best brushless DC fans with ball bearings, have a 35,000 hour lifetime (4 years, 24/7)

I have a GT, and on a shelf next to it, have a $10 fan that I expect to last at the most, 3 years, and will take me about an hour, and zero effort, to replace.

I am a bit of a techie type person too--but I also try to be a practical minimalist...

I honestly could not figure out what I would do with all of the data a computer would generate, did not want to dedicate a computer to log it, use the excess power to run the computer/logger, or purchase the (at the time) an overpriced LCD screen/logger.

Instead, I put that money in two extra (175 watt each) panels on my array (3kW PTC rated) and log the data at the end of the day with a pencil and paper--put it into a spread sheet to watch my total power generated vs used each billing cycle... Gives me an average (year over year) of an extra ~3kWhours per day and I save ~0.5 kWH per day on the logging computer (old laptop at ~20 watts).

However, if you are in California, to get the rebates you may (on smaller systems, must on >10kW systems) need to get electronic logging anyway.

Regarding the fan, it probably will only run 0-5 hours per day, but for every ~10C (~18F) rise in fan operating temperature over 20C (70F), lifetime is cut by ~half (1/2 per 10C is used in electronics design to derate for temperature based on typical activation energies for standard materials--it also works the other way--keeping things cooler extends their lifetime too).

So... assuming the fan runs at 122F (122F picked from an earlier post using external fan on a Xantrex inverter heat sink temp using an external fan for cooling).

(122-70F/18F)-1=1.8 122F life correction factor

35,000 hour * (0.5^1.8 temp-life derate) / (365D/yr * 5H/Day) = 5.5 years of estimated fan life...

The above makes a whole bunch of assumptions (rated hours of fan, fan ambient temperature, inverter temperatures, average fan operating time per day, etc.)--but does kind of confirm that in average warm conditions, that 5 years life from a top of the line fan in an inverter would not be an unexpected lifetime.

SunnyBoy says that their fan is "Convection with regulated fan cooling"--so expecting the fan to be on for 5 hours per day (probably much less) is certainly believable and would help extend the life of the fan (plus running the whole inverter cooler with the fan will extend the overall life too--hence the reason to add a relatively unreliable mechanical device like a fan).

I don't know what Xantrex or SunnyBoy (for example) design life is--but for both, their standard warranty is 10 years--hopefully the typical unit will last longer than that.

-Bill