[RE-wrenches] grid-tie inverters & generators

Kelly Keilwitz, Whidbey Sun & Wind kelly at whidbeysunwind.com
Thu Nov 20 14:09:59 PST 2008


Hi Dana,
I¹m hearing that it ³should² be OK, but to CYA install a relay.

We just secured a third such system ­ this one with the generator and
transfer switch 200 feet away from the inverter. Installing a relay on this
one would mean 200 feet of conduit through driveway and landscaping. Or,
maybe a wireless connection......? This one is a small array (1.9 kW) and a
large genny (~20kW), so I¹m inclined to think of the PV (if it even syncs
with the generator) as offsetting the house load, and not capable of messing
with the genny. I hope that¹s not just wishful thinking :)

Thanks for the explanation.
-Kelly

On 11/20/08 12:07 PM, "Dana Brandt" <dana at ecotechenergy.com> wrote:

> Hey Kelly,
> 
> I think that's probably the best solution. I don't think it should be
> necessary with Sunny Boys in gridtied system, but it's certainly the safest
> bet. I'm not sure if all SB's come with the right firmware, or if it's a
> special option, but they can be programmed to allow for a wide grid frequency
> window. This is used in the AC coupled arrangement with the Sunny Island. When
> the Sunny Island's batteries are full it starts to raise the grid frequency
> slightly. The SB's read this as an instruction to reduce their output and pull
> their arrays off MPP. At a defined frequency, the SB's shut down entirely.
> 
> So, the stories of SB's frying generators in off grid, AC coupled systems
> makes me think that the tight frequency window required for grid-tied systems
> had been replaced by the wider window used for communication with the Sunny
> Island. It was one of the first prototypes of these systems so it might be a
> little different now, but I installed a system that allowed the SI supported
> grid to range from 50Hz all the way up to 54Hz before the SB's shut down. That
> could allow quite a bit of backfeeding of the generator and might explain the
> generators being fried in these SI/SB AC coupled systems. I would think that
> with regular gridtied SB's they'd shut down before damaging the generator.
> 
> Bottom line, though, I'd probably install the NC relay powered off the
> generator input to be safe.
> 
> Dana

Kelly Keilwitz, P.E.
Whidbey Sun & Wind, LLC
Renewable Energy Systems
NABCEP Certified PV Installer
987 Wanamaker Rd, 
Coupeville, WA 98239
PH & FAX 360-678-7131
sunwind at whidbeysunwind.com
 


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