[aprssig] aprssig Digest, Vol 68, Issue 8

[Alex Carver]

A "grid-tie" system (which is what you describe is called) uses an inverter that must detect mains power before it generates energy.  The inverter uses the power on the mains to synchronize its internal oscillator so that the power generated by the panels and that on the main line is properly in phase with each other.

If the mains go out, the inverter will stop oscillating and then disconnect itself with a relay to prevent the mains line from being energized.  It has no ability to run on its own without some form of input from the mains.  In essence it has a sort of transfer switch installed but instead of transferring from one source of energy to another it just cuts off all the power.

Standard inverters do not have the phase synchronizing circuitry because they're designed for stand-alone operation.  Accidentally feeding the grid with a standard inverter (ignoring the possibility of energizing an otherwise dead grid) could set fire to the inverter if the mains come back out of phase with the inverter.

> From: "Dave Sparks"
> Subject: Re: [aprssig] 3' snow emergency (generators)
> 
> I wonder what precautions they take when back-feeding, such
> as with 
> photovoltaic solar systems, is done intentionally.
> 
> Dave - AF6AS
>