Summary: At any particular time, a country may produce less or more electricity than is actually needed. Interconnectors allow electricity to flow between a country with excess electricity to one with a deficit - i.e. to the market with higher pricing. The operator of an interconnector makes money through capacity auctions that give customers transmission rights - i.e. the right to use the interconnector.
Why this is important: The shift toward an electricity generation system dominated by renewables brings new challenges for the system operator. One of these is where do I get the electricity I need, if the sun isn't shining and the wind isn't blowing. One answer is to bring it in from places where its still sunny or windy. This might be in a different country, or a distant part of the same country - enter interconnectors.
The big theme: As countries move toward electricity generation systems dominated by renewables, the need for supporting infrastructure becomes greater. This will include battery/long term storage, demand management and interconnectors, which will enable balancing renewable electricity to be brought in from adjacent regions to offset periods of local shortage.
What is an interconnector?
An interconnector is a cable that connects the electricity systems or 'grids' of nearby countries or offshore renewable energy farms, most often offshore wind farms, to a country's grid.