If electricity sources far apart are connected then there can be huge benefits. A peak in one area can coincide with extra electricity in another.
One of the problems of supplying electricity it that in order to supply power with reliability, excess capacity must be built to cope with fluctuations. The there is the waste of spilled power when wind turbines must be closed down or street lights turned on during the day.
A power line connecting say Sydney to Perth would be about 3,000 KM long and cost $2 billion. AC current would lose too much energy, but High Voltage DC (HVDC) loses only 3% per 1,000 km or 10% for the complete journey. With spilled power being larger than that, and domestic power prices varying 5 times between day and night, 10% is not a large loss.
Such a line across the country would allow gusts of wind traveling across the country to be captured most of the way thereby giving wind power with less fluctuations.
Some calculations have been made showing that backup burning of biomas such as wheat straw would not be needed if this line was installed.
If the government built this line the private enterprise could build solar, wind, wave power and pumped hydro, etc, along the route.
The connection into the HVDC line is expensive so wind turbines cannot be continuous.
There are schemes to join the whole of Europe into one grid.
The Germans have plans to set up solar power stations in north Africa to supply their grid.
UK would have an advantage in power sharing with Norway. This graph shows the spread of power demand that could be reduced by sharing with Norway.