Hi Jeff,
Use Outback off grid inverters for the backup, and break the AC from
the grid tie inverters. An advantage of this is that you can use a
standard generator and transfer switch to charge batteries through
the off grid inverters. The grid tie inverters take care of the anti
islanding, etc.
Drake
At 10:11 AM 4/16/2010, you wrote:
Hope I have not posted this before, but it keeps coming up. We do
many systems that include a battery connected inverter and generator
to provide backup power for upscale homes. Although we have no
problem with roof mounted arrays, many of these homes may be large,
but usually are either shaded or their roofs are broken up with all
kinds of dormers and chimneys, with no large areas facing south.
In addition, many of these homes have large landscaped yards and
gardens up against the home, so we end up having to install a
ground-mounted solar array as much as 200 or more feet away. Since
we want to charge the battery from the solar array during an outage,
but do not want to run huge cable sizes due to the long wire runs
typical for low voltage DC arrays, we mount a SunnyBoy on the back
of the array, then run 240 VAC back to the
battery/inverter/generator system in the basement or garage using an
AC coupled design with relay cut-out to dis-connect on high battery
voltage during off-grid operation. (still not sure why inverter
manufacturers can't control over-charging from back-feed AC when not
grid connected).
Anyway, where to wire in the utility dis-connect that needs to be
near the meter base. The most logical is in the 240 AC output from
the solar array inverter before it enters the emergency loads
panel. However, there is still the matter of the battery inverter
which could easily backfeed the grid if programming is changed by
others. This would then require the dis-connect between the AC
output of the battery inverter and the house panel, but this would
kill the emergency loads panel if the utility actually decided to
lock out. Not likely, but still possible. Just concerned that code
officials will see the inverter in the house, a solar array in the
yard, and want a dis-connect that kills everything to grid.
Have any other states already addressed this issue?
Jeff Yago
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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