Grid Tied PV on Area Networks [RE-wrenches]

[Chris Anderson]

Wrenches,
 
We have run into an issue integrating grid-connected solar in some of
the older districts of Mass that have electricity grids comprised of
"area" networks as opposed to spot or radial networks.  It seems that
this type of network is not acceptable for interconnecting distributed
generation systems.  The issue appears to be the high level of
redundancy in the network as this type of grid is reminiscent of a peer
to peer computer network with individual electric consumers actually
being linked to one another.  
 
According to the Mass Tech Collaborative:
 
"An area network system typically serves a broader group of customers
located in a high-density area 
(such as a group of city blocks). Area network systems differ from spot
network systems in that they 
not only have multiple lines, transformers, and building connections but
also interconnections between 
the buildings. This means that power is flowing through even more paths
and in many different directions."
 
"...because area network systems allow power to flow through multiple
paths, adding a distributed generation 
generator to these systems introduces the risk of sending power into the
grid when the grid is not delivering 
power to the site, due to maintenance or system failures. This presents
significant risks to the safety of utility 
workers, performance of the distribution system equipment, and power
quality of other customers on the 
same network. Because of these risks, utilities must evaluate proposed
distributed generation on these systems 
more exhaustively than they do for radial interconnections."
 
In a technical bulletin on the MTC's webpage it states that:
 
"Area networks are designed to provide electric service that has a high
level of reliability and are more 
commonly found in urban territories.  By adding distributed generation
to an area network there is a 
possibility for reverse power flow through a network protector. [1]
This situation could adversely impact 
the safety of utility personnel, result in damage to utility equipment
and cause electricity fluctuations 
within the area network.[2]"
 
 
N-star (the utility) will apparently send us a letter with our
interconnection options. These may include: 
-Transferring your site's load from an area network to a radial
distribution system and interconnecting the generator on this system.
(not possible - this is an area network)
-Interconnecting the generator to a nearby radial distribution system
(again not possible given the lack of a radial dist system)
-Operating the load to be served by the generator off the grid (not
possible if we are to get a rebate for our clients)
 
 
So, does anyone have any experience actually installing solar on an area
network?
If not, does anyone have any thoughts on how we might?  
 
One thought might be to install some sort of current preventing diode
that would allow the system to be grid interconnected for the
grid-reference but prevent current from ever feeding the grid. Does
anyone know if this product even exists?
 
Thanks in advance!
 
Here are some further links about this:
 
http://masstech.org/cleanenergy/energy/glossaryelectricent.htm
http://masstech.org/cleanenergy/howto/interconnection/network.htm

 

 

 

Chris Anderson

Borrego Solar Systems, Inc.

 


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