Powering Rooftop Equipment with Rooftop Generation [RE-wrenches]

[Mark Robinson]

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  I'm looking for a way to install PV systems in commercial establishments
(like grocery stores) that need to avoid roof penetrations. I'm thinking of
using PV to power rooftop equipment with an Allen Bradley Motor Speed
Controller and a Nextek box. I've got an idea... If there are any holes in
it (big enough to throw a wrench through), I figure you guys will be happy
to point them out. 
 
    The motor speed controller usually takes AC, rectifies it to DC, then
inverts it back to AC at variable frequency to a variable speed motor. The
motor speed controller increases efficiency of the motor because it reduces
power to it when full load is not needed (VAV Blowers, manufacturing
processes, etc).

    I'm connecting the solar DC and the AC that used to power the equipment
to the Nextek power supply. The Nextek power supply takes all the solar DC
available and couples it to the DC bus in the Allen Bradley unit (bypassing
the rectifier section).  At night, the Nextek supply makes DC from the
utility just as the Allen Bradley would have and continues to support the
A/B DC bus. 

    We get no roof penetrations (assuming no-penetration solar mount) for
wiring, increased efficiency on the roof, and a very easy system to install.
Additionally, the rooftop power stays on in a daytime power failure (plus
battery backup could be added for a nighttime power failure). 

 
Possible problems...

    PV Shutoff - are we going to have to run a PV shutoff down the side of
the building? Would this reg apply where we're not supplying the grid? 

Other problems/thoughts/ideas?


Mark Robinson
 

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