Hybrid PV/Battery/Generator [RE-wrenches]

[Kent Sheldon]

Brad, I know of a handful of installations that have tied SMA Sunny Boy
inverters to generators. We haven't had any follow up phone calls saying
they didn't work. The SB inverters rectify the AC voltage sense to DC,
so this will normalize any error caused by ripple or harmonic
distortion, assuming it isn't bad enough to skew the true RMS value
greater than +/- 10%. One thing to watch out for: The SB inverter will
attempt to deliver current up to the limit of the inverter(s) tied to
the generator. If the load is not large enough to consume the current,
the excess will backfeed the generator, causing it to trip offline on an
over-voltage, or reverse current fault. This generally means that
grid-tied inverters are only tied to very large generators where the
load is known never to dip below the output of the available PV power.
In general, the larger the generator, the better its voltage fidelity.

Regards,

____________________________________________
Kent Sheldon
Manager, Industrial Power Systems
SMA America
ksheldon at sma-america.com
925 513 8813 Brentwood Office (Primary)
530 273 4848 Grass Valley Office




-----Original Message-----
From: Brad Bassett [mailto:bsbassett at earthlink.net] 
Sent: Wednesday, June 12, 2002 12:53 PM
To: RE-wrenches at topica.com
Subject: RE: Hybrid PV/Battery/Generator [RE-wrenches]

Antony,

The window of operation for a grid tied inverter is so tight now that 
the chances of one synchronizing with a generator is about nil. I saw an

attempt to get a 20 kW trace tech inverter to synch with a new 100 kW 
Kohler top of the line generator, and it never even came close. The 
longest I saw it try before an error on voltage (high and low) or 
frequency was about 3 seconds, and it takes 5 minutes of good power to 
synch. 

With a smaller generator such as would be used for a residence the 
chances would be even smaller. Still it might not be a bad idea to 
disconnect the inverter while on generator power to prevent any possible

backfeed of dirty power from the generator into the inverter (JB could 
this be an issue with SMA?).

Another option is to use a battery based backup system for critical 
loads, and grid tie inverters for the solar. I wonder if you could get 
them to synchonize with each other!? (Put the grid tie on utility side 
of backup inverter). Or a combination of battery based and straight grid

tie systems. With some musical relays you could transfer the solar aray 
from the grid tie to the batteries during an outage. I'll let someone 
else do that science project!

You also mentioned using a larger inverter, let me know if you find one 
that's not a scince project in itself.

Brad


Antony Tersol wrote:

> 1. If we go with straight grid-tie batteryless PV, we would need a
> transfer switch downstream, so that the PV wouldn't be running in
outage
> situation when generator is on.
> 



Brad Bassett
Schott Applied Power 
Tumwater, WA office
bsbassett at earthlink.net

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