[RE-wrenches] grid tied systems with seperate generator back up

[Patrick Shortell]

Hi Daniel,
Ive done this with 4- 5048 sunny islands. 2 per phase
generac smart switch service entrance rated transfer switch.
no critical load panel, output of islands feeds main panel, (100a)
On grid loss, Transfer switch opens, Islands take over from batteries/solar.
Aux relay in master sunny island spoofs genny controller, via relay, that
grid is still present.
generator does not start.
When batteries drop to 80%SOC, SI master relay pulls in genny
relay "tells" SI master genny is running and blocks reverse current (back
towards grid).
Genny runs till batteries are at 90% SOC.
When grid comes back, transfer switch closes, life goes back to normal.
Customer has 20kw of Enphase PV. Frequency shifting of islands controls
inverters.
After hurricane Sandy, he ran for a month without the genny even coming on
using whatever he wanted.His november consumption not very high.
Lights never blinked.
Customer is an enthusiast, not our typical customer.
this is a pretty simple sequence of operation but it took me forever to
wrap my mind around how simple it really was.
Generator and grid are tied together ahead of ac in terminals in the island.
Pat


On Fri, Feb 5, 2016 at 1:33 PM, Daniel Tittmann <daniel at greenwired.com>
wrote:

> Esteemed colleagues-
>
> We are finding more and more clients with existing utility back up
> generators that are wanting grid inter tied solar systems.  Many of these
> clients are not willing to go the extra mile to interface the solar system
> with the back up gen.  I am wondering if any of you out there have found
> simple fail safe solutions for preventing generator back feed when relays
> and switch gear are difficult or impossible to implement.
>
>  I have been thinking perhaps a large enough diode on the gen output could
> do it, but then what happens to the grid tied inverter when there is no
> where for the power to go?
>
> I know this is vague, but I am searching the hive to see if there is a
> better way to make these customers happy and make the sale.
>
> Thanks
> Daniel
>
>
> Daniel Tittmann
> CTO
> Greenwired
> www.greenwired.com
> daniel at greenwired.com
> 707-923-2001 (office)
> 707-206-5088 (Cell)
>
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-- 
Patrick A. Shortell
*Licensed Master Electrician*
*Certified Solar Installer*
71 Oregon Street
Long Beach N.Y. 11561
cell: 516-477-0221
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