Craig,
You can't install grid-tie solar inverters on a feeder supplied by a
backup genset...
particularly if the solar is large compared to the UPS loads and the
genset.
if you did, here's what I think would happen:
in grid-tie mode, the solar and everything else would work fine
but in "island" mode, when the grid goes down (or during genset exercise),
the genset would be supplying the regulated grid voltage to the loads and
the solar inverter. The load transfer would result in momentary a
voltage-frequency shift that would trigger the solar inverter to go off
line
for 5 minutes. Assuming the load and genset were stable, the inverter
would try to resume line-tie operation in 5 minutes. As the output ramped
up, (again assuming stable genset) it could supply UPS load... but only
if the UPS loads stayed equal or greater than the solar output. Once the
solar exceeds the UPS load, gensets can't convert excess power and turn
it into oil... and grid-tie solar inverters are not programmed to fold-back
output----so the grid voltage and frequency would start to increase in
response to the excess power. The grid-tie inverter would then detect
"grid" conditions outside of specification (+- 10%), and instantly drop
out... and then repeat the same steps starting with the 5 minute timer.
Typically, there'd be a cycle of fluctuating voltage and frequency, with
the solar inverters mostly offline. Not much benefit, and potential risk to
the genset, inverter, and any electronic devices being powered.
/wk
Date: Mon, 08 Jun 2009 22:49:18 -0500
From: craig gerald buttke <cr...@solarwerks.us>
Subject: [RE-wrenches] If anyone has input from an installer friend...
To: re-wrenches@lists.re-wrenches.org
Message-ID: <4a2ddbbe.7060...@solarwerks.us>
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
installers,
so as to not reivent the wheel.
any experience with connecting a grid PV system on the load side of an
automatic transfer switch?? fronius ig plus or sma's either one.
the genset is a natural gas that modulates with load-- so it is a step
up from a menards portable type.
assuming the solar is over producing the home usage (its a 10 kW system
so it could very well), the genset is still holding a "grid" albeit at
idle, the inverter will not necesarily know what to do except keep
wanting to produce "current (amps)".
who has already tackled this??
further there is talk of a battery system possible. but the 7 kW genset
would be stronger than a stacked pair of out back inverters, and or too
much capacity for the FM charge controllers to go to the battery.
comments?
Thanks,
Craig
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