Grid Tied PV on Area Networks [RE-wrenches]

Mon Mar 24 09:40:38 PDT 2008

<x-flowed>

I guess I just don't see the problem. It still seems that the anti- 
islanding, disconnect without utlity signal, etc. protections built  
into all grid tie inverters would prevent back feed if the grid was  
down. Your utility's explanation didn't really sound like more than  
the usual noise I have heard from utilities not familiar with solar.  
Could someone that knows about this explain why this situation is  
more problematic? I understand the grid layout, I just don't see why  
its a problem. It seems regardless of the complicated  
interconnections of buildings, etc. there is still no way to send  
power anywhere that the grid is not already serving.

Awaiting illumination,

Ray Walters

On Mar 23, 2008, at 9:09 PM, Ryan Mayfield wrote:

>
> Chris,
>
> I have done a design (not yet installed) that has a similar situation.
> Thankfully, the utility is relatively progressive and easy to work  
> with.
> Their requirement was to install a Siemens power meter (link below)  
> that
> drives a contact on the inverter circuit. The utility required that  
> if the
> building demand was < 10x the PV production, the meter would open the
> inverter contact. The 10X value seems a bit conservative but at  
> least it was
> a compromise. For this particular install it shouldn't ever trip  
> but if it
> were to happen often, I might be uncomfortable with the inverter(s)  
> cycling
> like that on a regular basis.
>
> This will require additional CTs for monitoring the building load  
> as well as
> a properly sized relay and contactor for the inverter circuit.
>
> Good luck.
>
> http://www2.sea.siemens.com/Products/PowerDistribution/Product/ 
> ACCESS-Power-
> Monitoring/Product/9300+Power+Meter.htm
>
> Ryan
>
> Ryan Mayfield
> Mayfield Solar Design LLC
>
> -----Original Message-----
> From: Chris Anderson [mailto:canderson at borregosolar.com]
> Sent: Sunday, March 23, 2008 5:47 PM
> To: RE-wrenches at topica.com
> Subject: Grid Tied PV on Area Networks [RE-wrenches]
>
>
>
>
>
> 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.
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
> - - - -
> Hosted by Home Power magazine
>
> To send a message: RE-wrenches at topica.com
>
> Archive of previous messages: http://lists.topica.com/lists/RE- 
> wrenches/read
>
> List rules & how to change your email address:
> www.mrsharkey.com/wrenches/etiquette.php
>
> Check out participant bios: www.mrsharkey.com/wrenches/
>
> Moderator: michael.welch at homepower.com
>
>
> No virus found in this incoming message.
> Checked by AVG.
> Version: 7.5.519 / Virus Database: 269.21.8/1339 - Release Date:  
> 3/22/2008
> 4:43 PM
>
>
> No virus found in this outgoing message.
> Checked by AVG.
> Version: 7.5.519 / Virus Database: 269.21.8/1339 - Release Date:  
> 3/22/2008
> 4:43 PM
>
>
>
> - - - -
> Hosted by Home Power magazine
>
> To send a message: RE-wrenches at topica.com
>
> Archive of previous messages: http://lists.topica.com/lists/RE- 
> wrenches/read
>
> List rules & how to change your email address: www.mrsharkey.com/ 
> wrenches/etiquette.php
>
> Check out participant bios: www.mrsharkey.com/wrenches/
>
> Moderator: michael.welch at homepower.com
>
>

R. Walters
Solarray.com
NABCEP # 04170442	

--
[Non-text portions of this message have been removed]

- - - -
Hosted by Home Power magazine

To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at re-wrenches.org

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------

</x-flowed>