[RE-wrenches] Utility Dis-connect for AC coupled Systems

Drake Chamberlin drake.chamberlin at redwoodalliance.org
Sat Apr 17 06:59:03 PDT 2010


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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