[RE-wrenches] grid-tie inverters & generators

[Dana Brandt]

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systems had been replaced by the wider window used for communication with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

-- 
Dana Brandt
Ecotech Energy Systems, LLC
www.ecotechenergy.com
dana at ecotechenergy.com
360.510.0433


On Thu, Nov 20, 2008 at 9:57 AM, Kelly Keilwitz, Whidbey Sun & Wind <
kelly at whidbeysunwind.com> wrote:

> All,
> I suppose a normally-closed relay on the inverter output, with coil
> energized from the generator (i.e. It opens when the genny is on) might be
> easier than a NO relay on the grid-side. Anyone do it this way?
>
> -Kelly
>
>
> On 11/20/08 9:30 AM, "Kelly Keilwitz" <kelly at whidbeysunwind.com> wrote:
>
> >
> > The relay seems like a reasonable solution. However, if the main panel is
> > entirely backed up by the genny, to power the relay from the grid (only)
> > requires a line-side tap, yes? Is there a simple solution that I¹m
> missing?
> >
>
>
>
>
>
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