ECN Forum Forums Code Related Discussion NEC & other Code issues What say ye??

Residential PV grid-tie; <12KW:

Could Article 705.21 (2008 NEC) be cited to require a disconnect on PV (solar) inverter output to grid-tie.

In other words a disconnect to remove solar AC from backfeeding into the utility grid?

And....what says it should be outside, on exterior of resi??

Grid tie inverters will not run without the grid being present. I am not even sure they have the 60hz time base to make power without the grid (they use the grid to pace the inverter?). I assumed that was why they wouldn't put out.

This is the impression I got from the people trying to sell me a system anyway. I did want off grid generation in an outage and they said not with a grid tie inverter.

This is one of those things I would fall back to the manufacturer's instructions on. They know what their box is supposed to be able to do.
I am not sure if this is part of the listing standard.

The white book wasn't much help QIIO says basically "install it using the instructions" and the grid connect inverter part throws you back to the off grid inverter section so it does appear that how this shuts down is not part of the listing standard.

It is my impression that the units are designed to back-feed a breaker in the panel, and this serves as your disconnect.

I'm not completely happy with this as the only disconnect - I'd like an 'off switch' and OCPD at the collector panel as well - but that's another matter.

I wonder if the manufacturers of grid tie inverters have have models that can change between grid tie and non grid tie by means of an external contact. That way, when the inverter is connected to the grid it can backfeed. When the grid goes away, a contact on the grid fed isolation switch allows the inverter to restart and power up local loads up to the capacity of the inverter.

Other choice would be a large UPS backed up by the PV and battery system.

Larry C

My understanding is that EUSERC policy excludes the installation of any such scheme.

Renosteinke

Out my way the inverter has to be co-located VERY close to the panel.

EUSERC utilities insist upon such. The idea is that upon the event of fire/ wiring faults the first responders can kill the power source with no more than two throws.

EUSERC is not at all concerned about anyones desire to have partial power when the grid goes down. Their concern is their own employees. Having studied the issue at some length it has been resolved that it's their way or no power for you!

It is futile to try and jigger around their scheme. Once any such contraption is discovered the spanking will be too severe to bear.

The subsidy went away so I put my solar plans on hold but I had decided that I would put transfer equipment in and use 2 inverters if it came to it.
I did wonder if you could "tickle" the grid tie inverter with a regular 12v inverter to light it up after the real grid was switched away. I am just guessing but I suspect the solar inverter looks for voltage coming in on the utility side at each zero crossing and does not gate the solar inverter if it doesn't see something. I suspect the problem would be that your 12v inverter could not push into the attached load hard enough to get things started.
The real answer would probably be 3 pole transfer equipment switching both phase legs and the DC output to a non-grid tied inverter.

Tesla, your understanding of EUSERC rules must be flawed.

UL has already listed a number of 'micro inverters.' These are located at the solar panel; several can combine their outputs into a single feeder to a back-fed breaker at the panel.


It's not so much trying to 'jigger around their scheme' as a matter of technology being out of step with technology. It doesn't help that 'policy' is partly driven by acolytes of "Green Religion."

Yes, those units can be sold OUTSIDE EUSERC utilities.

In fact, there are no end of non-EUSERC UL listed products.

EUSERC prohibits many practices acceptable to the rest of the industry.

At a certain point the customer is going to exert some rights about what they can do on the load side if the meter. I am old enough to remember when the Telcos prohibited connecting anything to a phone line that they didn't rent you. That went away too.
I understand they need some standards of safety and the ability to protect the integrity of the grid but we can't let them get silly here.