[RE-wrenches] off grid PV connected to generator

[Phil Undercuffler]

Eric,

Good questions, and you hit on a number of topics so let me see if I can
address them one at a time, not necessarily in chronological order.

Yes, the optimal application for the GTFX / GVFX inverter series is grid
tie with battery backup.  If you just want backup to the grid, the
traditional FX is a great solution.  If you need extended run-time and want
to integrate a generator, then the Radian series is a better solution
because it can not only integrate both grid and generator, but it can
change its operating parameters based on which input it's connected to.

The SW, XW and Radian inverters are all capable of operating on-grid
(grid-interactive or backup) or off-grid (with or without a generator).
 However, none will automatically disconnect the PV when the genny
auto-starts, nor would I suggest that they should.  Realistically, the
system should only start the genny when the batteries are near depletion --
if it's started, the batteries need all the help they can get.  Rather, the
generator should only be disconnected (turned off) when the batteries reach
the absorb setpoint.  BTW, I can't speak for everyone but none of those
inverters have that functionality, at least not yet.

With 600 Watts of connected PV, I wouldn't worry about disconnecting the
PV.  Even with a small battery bank, the sun will set before that size of
array drives the bank anywhere close to an absorb voltage.  Add another
zero to the PV size and my answer would be different, of course.

Also, if you do wind up installing an automatic transfer switch with a
battery-based inverter system, don't allow the ATS to control the generator
starting, even if that flies against every tradition of the generator sales
guy.  You don't want the genny running through every minute of the power
outage, you want the system to start the genny only when the batteries are
low.

Good luck with it, and enjoy the sun!

Phil



On Tue, Jan 15, 2013 at 1:50 PM, SunHarvest <eric at harvesthesun.com> wrote:

> Further, I recently installed a GVFX for a customer. I'm hearing from
> certain sources that the grid-tied line of inverters from Outback are not
> designed to interface with a generator. Really??
>
> I was told by Outback to install a transfer switch line/supply side of the
> inverter; that this was the only way to interface the genny with the
> inverter; that the AC Hot In could come from grid or a genset. And indeed,
> this is the only way I can figure out how to get the genny to charge the
> batteries when the grid goes down. But then again, I don't have the
> extensive electrical background that allows me to think outside the box as
> often as I would like...that's why I'm posing my query here for the pros.
> In this Outback install I have to again advise the homeowner to open the PV
> breaker to the inverter during generator operation, right? Even though he
> has a modest 600W (STC) array and an 8.5kW Kohler genset. Hardly the
> opportunity for solar to feed back to the genny under the most sunny and
> cool of days. I'm more concerned with the Enphase install.
>
> The Xantrex SW series inverters are fully capable of operating on-grid or
> off-grid with a genset. So do those inverters automatically disconnect the
> PV when the genny auto-starts? And with the Outback, is the Mate supposed
> to do the same (as long as the genny is operated by the auto-start and not
> a transfer switch)?
>
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