Views on SMA Sunny Island concept

[stephendv]

Hi All,

I'm new to off-grid power and would like some opinions on the SMA Sunny Island systems:

http://www.sma-america.com/solar-technology/products/island-grids/battery-inverters/index.html

The differentiating factor with this technology is that you can connect multiple energy sources on the AC side of the inverter.  This means that the system is easier to expand in the future and since it's all AC a regular electrician can do it and the wire lengths are not such an issue.

But it seems fairly new and I've heard bad things about the construction quality of the windy boys.  The SMA literature also has examples where, using the sunny island, you connect additional PV arrays using sunny boys to the AC side of the network.  This seems as though it must lose efficiency when you're charging the batteries as you're converting from DC to AC then back to DC again?

(Or is it a clever business maneuver to get you to buy more inverters!?)

Opinions please

Stephen

[David HK]

Like all the other people that visit this site daily, I do enjoy reading some articles.

It does however tax the mind when people use abbreviations. For the benefit of my self and other users that may post at another time on different matters may I implore you not to use abbreviations - write things out in full and then show the abbreviation.

What does SMA mean in the context of your letter before one leaps to click on the URL?

David HK

[stephendv]

Hi David, SMA is the name of a company that manufactures inverters.  The only other two abbreviations I've used are:

AC: Alternating Current

DC: Direct Current.

[DamonHD]

SMA is the name of the company:

http://sma.de/

Rgds

Damon

PS. I like the scheme described, and if we generated more power and/or had half-hourly metering or whatever, then I would consider one myself.

[stephendv]

Ok, I received a brief spec from SMA Germany for a complete off-grid PV + genny solution.  Here are the two options they provided:

1. st offer (AC coupled):
   
2. ,5 kWp PV modules (angle 40º if they are free mounted)
   
1. x SI3324
   
1. x SB2500
   
1. x SI - BatFuse
   
1. x Battery bank 600Ah@24V (C10)
   
1. x Diesel generator 3 kW
   
2. nd offer (DC coupled):
   
2. ,4 kWp PV modules
   
1. x SI5048
   
1. x SRC40 - MT (charge controller)
   
1. x Battery bank 400Ah@48V (C10)
   
1. x Diesel generator 3 kW
   
   

Notice the bigger PV and battery bank for the AC coupled system?  

So I'm starting to get the impression that the AC coupling does have a performance cost (not to mention the cost of an additional inverter).  On the plus side, it gives you loads of flexibility and ease of expansion.  The SMA marketing material targets the Sunny Island kit at complete island grid networks (e.g. a remote village) where such considerations are perhaps more important than the raw efficiency of the system.  

On the down side, it costs more and is not as efficient as a DC coupled system - so may not be as suitable for a single off-grid home.