Solar Power

[Gaffen99]

If there is a power loss from the utility, is the solar power feed disconnected from the grid and how is this accomplished? Just wondering.

 

[LarryFine]

Most, if not all intertie inverters disconnect from the utility power when it's lost.

How, exactly, I don't know, but I do believe it's a requirement.

 

[Pierre C Belarge]

Yes, they are disconnected from the grid upon the unit sensing loss of utility power.

 

[bphgravity]

See Part VII. Connection to Other Sources, specifically 690.61 of the 2008 NEC...

 

[dbuckley]

Most, if not all intertie inverters disconnect from the utility power when it's lost.

The requirements to stop potentially dangerous backfeeding are articulated in IEEE P929 "?Recommended Practice for utility Interface of Photovoltaic (PV). Systems". Given the dangers of backfeeding to utility company staff, any utility that doesn't mandate anti-islanding provisions would be reckless in the extreme.

How, exactly, I don't know, but I do believe it's a requirement.

Black magic, mostly.

The earliest designs of systems that could detect islanding monitored the utility voltage on each cycle, and only once the utility halfwave voltage reached a few volts was the inverter half-cycle started. Unfortunately, the realities of power factor and harmonic distortion make this simplistic system unreliable, so there has been oodles of work to find better ways of detecting when an inverter is islanded.

A search on IEEE explore for inverter islanding gives 213 hits

 

[iwire]

I have looked over many utility PV interconnection agreements and they all require UL 1741 listed inverters.

UL 1741 matches up with IEEE 1547.

 

[dbuckley]

Yeah, the IEEE 1547 series is probably a better source, but its a much more political animal in that it had the need to keep many competing interests happy.

 

[BillK-AZ]

The basic anti-islanding technique is to have the inverter try to slightly lead the utility voltage and phase. If the utility connection is present this will require more current and can be detected within a few cycles. The same logic is used to keep the voltage and frequency withing the prescribed limits.