Upgrading an existing system

[MAbbott]

I had a solar system installed at my residence in Texas a bit over 10 years ago and got all the various tax subsidies putting it in. It's basically a 3KW system consisting of 18 170W Suntech panels and a Xantrex inverter. The original installer are not around anymore and after contacting a few solar companies, pretty much none in my area want to touch an existing residential system.

So, the Xantrex inverter decided to stop working over the summer and I just got around to replacing it with a SBA Sunny Boy 6.0 inverter which I'm pretty pleased with. The install and bringing it online was very straight forward but since this system has room for 3 DC inputs and I'm using 1 of them, I'd like to start adding some panels. I should have around 3KW of room to add panels but am stuck on which panels to purchase that are compatible with the SBA inverter.

I was not terribly involved in the installation of the existing system so I didn't pay as much attention to the specs and design as I should have so based on these values in the manual: max PV array power as 9600W, max voltage as 600V and Max power for any input as 10A here are my questions:

1. Does the 9600W mean that it's allowing for the loss of the inverter in the process so I can oversize the solar array (i.e. greater than 6KW listed as the AC output) to deal with the lossy nature of going from DC->AC?
2. The 10A limit has me somewhat concerned in looking at current panels. I was looking at a LG 400W panel that lists it's DC amps (IMPP) at 10.31 which I think means I can't use that particular panel and also precludes me from doing any kind of parallel install with these larger panels. Is my assumption correct on this?
3. Any suggestions on angling the panels (whichever I wind up going with). I've got a carport with a metal roof that's ~35'x25' and right next to the inverter so is quite convenient to stick panels on top of. It's flat (not just flat sheet steel but the corrugated panels for metal buildings) so I need a want to angle them at least 30deg as far as I can tell from my reading. My concern is wind loading, this is hurricane country and it just seems like having a panel up in the wind on a flat roof is just asking for problems.

 

[MarkSolar]

1. Does the 9600W mean that it's allowing for the loss of the inverter in the process so I can oversize the solar array (i.e. greater than 6KW listed as the AC output) to deal with the lossy nature of going from DC->AC?

Generally you oversize the array by about 30%. Inverters will usually tell you how much they can handle, I'm familiar with Fronius and they indicate they can handle 150% of their rated power input. The oversizing is to optimize power production during times when sun is not optimum. It's really a balancing act between how much you spend on panels vs how much power you'll be able to produce on a given day of sun.

2. The 10A limit has me somewhat concerned in looking at current panels. I was looking at a LG 400W panel that lists it's DC amps (IMPP) at 10.31 which I think means I can't use that particular panel and also precludes me from doing any kind of parallel install with these larger panels. Is my assumption correct on this?

The inverter will limit the current to 10A, you're fine with those panels. The inverter will do what is called "clipping", which is throwing away some of the power that's being fed into it from the panels.

3. Any suggestions on angling the panels (whichever I wind up going with). I've got a carport with a metal roof that's ~35'x25' and right next to the inverter so is quite convenient to stick panels on top of. It's flat (not just flat sheet steel but the corrugated panels for metal buildings) so I need a want to angle them at least 30deg as far as I can tell from my reading. My concern is wind loading, this is hurricane country and it just seems like having a panel up in the wind on a flat roof is just asking for problems.

If you're in hurricane country you should probably have an engineer check your carport, you might end up with the panels carrying the whole carport away. The angle has less impact on production than you might think, you might find it makes more sense to use a lower angle and add an extra panel. Panels are often cheaper than adding mounting hardware and beefing up the roof to keep it from blowing away. There are online tools that will do the angle calculation for you.