[RE-wrenches] Sunny Island retrofit

Thu Jul 3 20:01:22 PDT 2014

Mac,

Be careful with breaker sizing here. The transfer switch in the SMA SI5048
is only rated for 56A at 120 VAC. From the SI manual:

“The maximum input current allowed on the Sunny Island is 56 A. Higher
input currents must not be connected to the Sunny Island.”

To protect that switch properly, you would need to use a 50A breaker
(unless you can find a 55A breaker that fits in your AC panel). Since most
common AC breakers are only rated for 80% duty, you would need to limit
that 50A breaker to a continuous 40A load. That’s more than the max output
current of the Fronius 10.0-1, although it’s debatable that the output of a
PV inverter is “continuous”. It certainly could be in some situations,
especially with a tracker mount, although even with a fixed array, you
could see max rated output for at least a couple of hours per day.

I agree with the suggestion of putting part of the PV array on a 5kW Sunny
Boy, or adding a second Sunny Island and using two Sunny Boy 5000’s. Using
two Islands would eliminate the need for a transformer, and allow for full
array power during grid outages.

Brian Teitelbaum

AEE Solar

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *Mac Lewis
*Sent:* Thursday, July 03, 2014 9:34 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Sunny Island retrofit

Hi Wrenches,

Jerry, I think you are correct, sma gear all around would be best.  This
will be my recommendation but I am sensitive to this substantial cost.

Dave, if I add the second Sunny Island, I don't think I will be throttled
back because the transfer relays are rated for 60A.  This should pass the
full current of the output of the Fronius, which is 41.7A.  My concern is
more during backup mode, if the Sunny Islands could "trick" the Fronius
into staying on line.  I would add either load dump relay control or an AC
interrupt relay to knock the Fronius off-line if the batteries were full,
in addition to the frequency shift control that the Sunny Island offers.

Thanks for the input, I'll shoot for all SMA gear.

Thanks

On Thu, Jul 3, 2014 at 9:23 AM, Dave Click <daveclick at fsec.ucf.edu> wrote:

Mac, that Island interconnects with a max 70A 1P breaker (6.7kW
continuous), so unless they have a constant critical load draw or the
Fronius is massively oversized, you probably don't want to AC couple the
Fronius. The 5048 is also able to output a continuous 5000W only when it's
cooler than 77F and it derates above that (4500W at 95F, for example). I
don't believe its surge ratings apply to the AC2 output back into the
utility but they probably wouldn't be enough, anyway. I think that whenever
the Fronius output reached about 6000W, the SI would shift its frequency to
switch the Fronius off. Cheapest may be along the lines of your first
option-- not sure what the PV stringing is like but maybe you could move a
string or two off the Fronius and put it onto a new Sunny Boy with an
autoformer. Since I imagine this system doesn't have PV WIRE on the module
leads or home runs, officially I'd recommend a classic Sunny Boy. Then
leave the Fronius as-is.

Unless of course the customer thought they were buying a system with the
full 10kW supplying critical loads when the utility is down... then the
original contractor is stuck with buying the second SI they should have
installed in the first place.

DKC

On 2014/7/3, 10:46, Mac Lewis wrote:

Hello wrenches,

I wanted to run this scenario by the forum.  I have spoken with SMA about
this, but want some other opinions.

We were recently contracted by a fellow solar company to do some warranty
work for them out of town on a Sunny Island system that they had installed
about 5 years ago.  It was VERY poorly implemented originally and was never
installed as SMA intended.  In fact, during a small power outage, the only
loads that never came back on after the utility was back on line were the
loads in the critical load panel.  Oops.

Anyway, our job is to get it working properly for the least amount of cost
possible.  They have a Fronius IG Plus 10.0 fed into a 400A service panel.
 The Sunny Island 5048 AC Input also comes off of this panel and feeding a
120V only critical load panel.  Please note that there is no solar fed into
the AC output side of the Sunny Island, because there is not 120/240
available and thus there is no possible way for this system to utilize the
solar while the grid is not present.

I see two options (but there may be more): pull out Fronius, put in Sunny
Boy inverters and an autoformer, wire properly.  Another option is to add
second Sunny Island and try to AC couple the Fronius with the two Sunny
Islands.  The second option is less expensive overall, but I'm hesitant to
rely on AC coupling with the Fronius.

I'd appreciate any thoughts on this.

Thanks

-- 

Mac Lewis

"Yo solo sé que no sé nada." *-Sócrates*

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"Yo solo sé que no sé nada." *-Sócrates*
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