[RE-wrenches] off grid PV connected to generator

[Dave Click]

Well summarized. I think your mileage would vary based on the 
anti-islanding algorithm used in the inverter and the generator's 
ability to regulate frequency. So while it may "work" in that an 
inverter syncs to a small generator's output, it's very unlikely that 
reverse current backfed into the generator was considered during the 
generator design. Feeding 3kW of PV back into a generator that had 6kW 
of load isn't going to drop your fuel consumption by 50%, either. Given 
that the best case scenario is marginal fuel savings and the worst-case 
scenario is a fried regulator board taking your generator offline when 
you need it most, I'd keep them separated.

DKC

On 2012/12/13 10:18, August Goers wrote:
> Hi All --
>
> Thanks for the feedback. Yea, we've always used Sunny Islands with
> batteries for anything that needs to run off grid. This was more of just
> a theoretical question. From what I heard, it sounds like the excess
> current from the PV might damage the generator (or I suppose anything
> running in the house) and this will result in higher voltage. Best case,
> the inverter will cycle on and off. V = I*R. Worst case something blows up.
>
> Thanks, August
>
> *From:*re-wrenches-bounces at lists.re-wrenches.org
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>
> [mailto:re-wrenches-bounces at lists.re-wrenches.org
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *Greg
> Seelhorst
> *Sent:* Wednesday, December 12, 2012 8:18 PM
> *To:* 'RE-wrenches'
> *Subject:* Re: [RE-wrenches] off grid PV connected to generator
>
> August –
>
> I’ve seen this scenario and it is not pretty like William suggests.
>
>  From what I’ve seen, the problem is not so much the power of the PV
> being more than the generator, but moreso if the 1) generator is
> synchronous or non-synchronous with the inverted AC (sine wave) and 2)
> if the loads are less than the PV.   The generator will ‘create’ the
> voltage and run even if there are zero loads.  The inverted AC (from PV)
> wants to push current onto the ‘local grid’ and if there are no loads
> (nor heat sink diversion or batteries to charge) then the current will
> try to backfeed the generator.
>
> My recommendation is to get a critical loads panel for the generator
> only back-up, or go grid-tie with back-up using a Sunny Island, or the
> like, that make the switch seamless during an outage.
>
> *Greg Seelhorst*
>
> /Designer/Project Manager/
>
> NABCEP Certified Solar PV Installer™
>
> *POSITIVE ENERGY, Inc.*
>
> 510 S. Main Street
>
> Las Cruces, New Mexico 88001*
> *Cell: 575-650-1883
>
> Office: 575-524-2030
>
> FAX:575-915-1788
>
> *gs at PositiveEnergySolar.com* <mailto:gs at PositiveEnergySolar.com>
> www.positiveenergysolar.com </www.positiveenergysolar.com>
>
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> <http://www.positiveenergysolar.com/>
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