According to initial IESO data there were some records set by wind generation in Ontario on January 4th 2013 - as there was on New Year's Day 2012, and January 1st 2011.
On January 4th, industrial wind turbines in Ontario produced a daily record of ~36,873MWh.
An hourly record of 1640 MW was set in hour 18.
At hour 18 Ontario was a net exporter of 2086MW, and the Hourly Ontario Energy Price (HOEP) was $24.32/MWh - if all the wind output was purchased at the initial feed-in tariff (FIT) price, the loss on exporting the wind power in that one hour would be ~$181,500.
The average HOEP for the day was $22.07/MWh, which, under the same assumptions the day's revenue for wind generators on the IESO-controlled grid at ~$4.8 million, with the resale value at ~$800 thousand.
A $4 million loss.
Dispatchable coal and natural gas units were also generating on the 4th, and all but 5 hours net exports also exceeded the amount of dispatchable generation - so the export story is certainly not exclusively about wind turbines.
The reason the dispatchable coal and natural gas-fired generators need to be available may be explained by wind production 47 hours prior to the record set on the 4th; when Ontario demand was higher than it had been for 118 days, the grid-connected wind resources were producing only 234 MW. As it was dark at the time, and assuming the non-grid wind turbines were producing at the same efficiency as the turbines on the grid, Ontario's 2500+MW of renewable energy was outputting only about 10% of capacity at peak.
That explains why the dispatchable generators need to be available.
This generation frequently operates for export customers because Ontarians pay the full operating and capital costs through the global adjustment mechanism. This explains why the net exports are frequently higher during the higher demand periods of the day than the low demand of early hours.
That does not explain why net exports could be lowered by high winds.
Perhaps the markets we export to also have more supply than anticipated when the wind resource is plentiful - and perhaps that will increasingly be the case.