[RE-wrenches] 2 PV utility interconnect disconnects?

[Kurt Albershardt]

On 2/21/09 10:24 AM, Joel Davidson wrote:
> January 1, 2009 LADWP added another interconnection requirement. See 
> page 8-11 at http://www.ladwp.com/ladwp/cms/ladwp004344.pdf

I found what I think is the relevant section on p. 36 of the PDF (called 
out as p. 1-32 at the top of the page.)


> This is how a PV commercial project manager described this new 
> requirement:

I'm curious if this was an LADWP project manager, or someone managing 
projects for customers?


> When a customer, any customer, generates electrical power with the 
> intention of supplying that power to the electrical grid, the 
> connection to the grid has to be made below, or on the load-side, of 
> one main switch for the property.

They define

/generators using a closed-transition (“make-before-break”) type 
transfer switch or a multi-
breaker transfer scheme, or an electrical inverter that can be 
configured to operate in a utility
interactive mode constitute a potential back feed source into the 
Department’s electric system and are
classified as interactive generators.
/

> the policy seems to be that the total electricity supplied to any 
> building or property must be disconnected from the grid by one main 
> switch.

The wording appears to be:
/
  All interconnected generating systems shall be connected on the load 
side of the customer’s meter switch (main service disconnect device).
/
I'm wondering about the origins of this requirement.  How would they 
handle critical power systems (data centers, hospitals, etc. which are 
often fed by multiple services entering by different routes?)  How would 
they handle a premises with multiple service voltages?



> This policy is in place for emergency situations, to where fire 
> fighters or persons on the scene during an emergency would be able to 
> completely shut down building power with one switch. 

The phrase "pull the meter" comes to mind here...



> This describes a scenario whereby the grid is disconnected from the 
> building circuits, but the solar PV is still connected to the building 
> circuits. Therefore, there is a basic flaw in this requirement; this 
> scenario is only possible at nighttime- during the daytime, the solar 
> PV system is energized and may still feed to the building electrical 
> circuits, unless the main PV disconnect switch is opened.

Has this "project manager" ever heard of anti-islanding?  This fantasy 
scenario almost makes sense for a battery-backed PV system, but then the 
presence or absence of sunshine would not matter.  What about emergency 
backup gensets and UPS or flywheel systems?  They are protected from 
backfeeding by a transfer switch, so exempted, but UL 1741 does not 
qualify as such?








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