On 02/05/2013 16:26, harry wrote:
Grid tie inverters generate whatever frequency they "see" on the gird
connection. So their operation has no effect of the grid frequency.

However the local voltage changes.
My PV panel increases local voltage (in my house) by around 2 volts
when running flat out.
My 16Kw shower drops the local voltage by seven volts when in use.

If I lived in town, it would be less than that. There would be larger
cables and transformers.

Yeah but we had that discussion. Voltage swings cause frequency changes,
unless you take steps to compensate for them - more coal in the boiler,
or fiddle with the exciter current.

So even though your devices are not in themselves causing a frequency
swing, they are causing a voltage swing, and that causes spin speed
instability in synchronous rotating generators.

Andy