Photovoltaic connection to back up gen

Hi All
Ran into an instance today working with another electrician on a grid tied photovoltaic job on an out building that would be Tied into a single family home that was equipped with a back up whole house generator
I do not know of a reason why the photovoltaic system could not be tied in at the out building and back feed to the house on the load side of the ats assuming the proper disconnects and labeling is in place.
My counterpart feels that it would overload the generator and or inverter
I don’t see it.

Anyone have any experiences with this ?
Thanx Dj
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I have no direct experience with this, however there are several discussions of the topic on this board.

The issue is 'what happens when you are on generator but the PV system is producing more power than the load is consuming?'

When the PV system is grid tied, the power simply flows to the grid.

When the PV system is tied only to the generator, then you have a problem. Generators are not designed to absorb power, and most PV system are not designed to reduce their output. So something has to break. If you are lucky, then the system voltage starts to rise, and some safety limit shuts something down. If you are not lucky, then you let the magic smoke out of the inverter, the generator, or both.

If the PV system and generator are designed from the get go to work properly together, then this could in theory be done. The PV system would 'simply' need to use the PV array less efficiently and reduce its output so that the generator load never goes below minimum. But 'simply' means lots of engineering work to accomplish.

-Jon
 

tortuga

Senior Member
Location
(44.057116, -123.103394)
Occupation
field supervisor
I do not know of a reason why the photovoltaic system could not be tied in at the out building and back feed to the house on the load side of the ats assuming the proper disconnects and labeling is in place.
Thanx Dj
See 110.3(B) The inverter manufacture would need to approve of it.
A standard grid tie inverter has a impedance sensing circuit and would probably just go off line during transfer and not engage with the generator.
Its pretty common around here;
We use a 2nd inverter called a sunny island, and a battery bank to interface with the grid tied inverter and the generator.
 

MJRobinson

Member
Location
Chico, CA, USA
We deal with this all the time if you want solar and the generator on the same panel, install an interlock on the panel so either one is off or the other. If they want an automatic transfer switch installed the solar should be on the utility side of the switch.
 

GoldDigger

Moderator
Staff member
We deal with this all the time if you want solar and the generator on the same panel, install an interlock on the panel so either one is off or the other. If they want an automatic transfer switch installed the solar should be on the utility side of the switch.
Which, depending on the location of the ATS, may make it the new Service Disconnect, with consequences on the wiring of the original panel. And the PV may be a line side PV connection which POCO may or may not allow.
 

MJRobinson

Member
Location
Chico, CA, USA
Which, depending on the location of the ATS, may make it the new Service Disconnect, with consequences on the wiring of the original panel. And the PV may be a line side PV connection which POCO may or may not allow.
So true. Most of the Gen installs require the movement of all circuits to a critical loads panel.
 

Pscanlin

Member
Location
Houston, Texas
Occupation
Electrical Designer
We deal with this all the time if you want solar and the generator on the same panel, install an interlock on the panel so either one is off or the other. If they want an automatic transfer switch installed the solar should be on the utility side of the switch.
Depending on the TDU, we typically tap the pv inside the ats
 
Top