question regarding grid tie inverters?

[PNW_Steve]

Hey Everyone,

I was poking around looking at solar gear and ran into a question that I could not answer.

What does your grid tie inverter do when the utility power fails? I couldn't find a solid answer but a number of statements in the info that I was reading gave me the impression that if you lose utility power that your grid tie inverter would stop providing power.

From what I can see, if I had grid tie solar and the utility power goes out then I would still have to start my generator and hit the transfer switch to simulate utility power.

Do I understand this correctly?

Thanks

S.

[DamonHD]

Most grid-tie inverters will cut power when the grid goes down to avoid attempting backfeeding the local grid and making things live that should not be.

Some specialised inverters can disconnect the load from the grid and continue supplying it, usually with some form of battery to help match generation and load.

Rgds

Damon

[PNW_Steve]

Most grid-tie inverters will cut power when the grid goes down to avoid attempting backfeeding the local grid and making things live that should not be.

Some specialised inverters can disconnect the load from the grid and continue supplying it, usually with some form of battery to help match generation and load.

Rgds

Damon

Thanks Damon,

That is what I "thought" that I was reading. I questioned my understanding because, while preventing back feed is absolutely necessary, I thought that it would be downright stupid not to some method of sensing line condition and isolating the utility while continuing to supply the load. Provided that there is continuing input to the inverter from solar, wind or batteries.

As I assumed that they would not do something that appears that ridiculous to me then I must be misunderstanding....

I was in fact understanding properly just not believing it could be.

Thanks again.

[PNW_Steve]

Another comment on the subject:

We have very frequent and long lasting (IMHO) power outages here. We all have generators to deal with it and most of my neighbors have double male ended power cables for their generators that they plug into the generator and in to a receptacle in their home. Hoping that they remembered to open their main breaker.

I think that this is a BAD practice and will, without hesitation, scold anyone I see following this practice.

Two weeks ago I ran into an  old friend of mine that is a recently retired lineman for an electric utility. Our conversation wandered about and landed on this subject. His take on it was that unless the outage was caused by a break in your own service trop then, if you failed to isolate, the generator would "see" the load from all of the customers between you and the point of failure. In that case the typical generator would immediately trip its overcurrent protection. He was much less concerned about the issue than I was and he is the one out there in the rain and wind climbing the poles to fix our power.

Now I still do not condone connecting a generator without some sort of proper safety interlock such as a transfer switch or simply running extension cords to critical devices.

Just my $0.02

[DamonHD]

Use your favourite search engine to look for "widow-maker cord".

The reason that most grid-tie inverters simply shut down when the grid fails is that that is cheaper and more efficient (an d simpler and safer) than one that can isolate from the grid and manage batteries and other power sources.

Rgds

Damon

[boB]

And normally when the "grid goes out", if the  neighborhood is still connected, even  if the GT inverter doesn't anti-island (turn off), the inverter would be seriously overloaded (shorted) and it would just stop producing immediately.

  In fact, it might not even be able to energize the pole transformer.  That is, if it is the typical <10 kW home GT system.

boB

[dnix71]

PNW_Steve It's called "grid-tie with battery backup" The cost is about 15% more than no battery backup. There is also "grid-assist with battery backup" Grid-assist is useful in places where grid tie is not allowed. You run from what you can make and take the rest from the grid (if available).
http://solar.schneider-electric.com/solution/residential-grid-tie-with-backup-power/
http://www.wholesalesolar.com/grid-tie-battery-backup