A 260-mile sub-sea electricity link between Scotland and Wales will support 450 jobs during construction.
The £1.3bn Western Link HVDC (high-voltage direct current) link will run from Hunterston power station on the west coast of Scotland to Connah's Quay on the North Wales coast and will have enough capacity to power four million homes a year when it goes online in 2016.
The link is bi-directional so that England and Wales can access Scotland's renewable energy and power can flow the other way "when the wind doesn't blow" in Scotland, Energy Minister Michael Fallon said.
"The Western Link is a perfect symbol of the single energy market, of which Scotland is part," he said, during a visit to view the start of work at the Hunterston site today.
"It will enable English and Welsh consumers to access Scottish renewables and enable Scots to benefit from base load power when the wind doesn't blow. This world-leading, billion-pound under-sea connector shows the strength of our current integrated system."
The project is a joint venture between National Grid and ScottishPower Energy Networks (SPEN). The £1bn main contract to build the Western Link has been awarded to a consortium of Siemens and Prysmian.
SPEN is also investing £2.6bn in network upgrades to 2021 with a further £5bn proposed between 2015 and 2023 across central and southern Scotland, Merseyside and North Wales. The combined investment will provide "thousands of jobs over the next decade" the firm said.
This programme will result in the renewal and replacement of over 15 per cent of the firm’s existing substation assets, replacement of about 500 miles of overhead cable and an increase in Scotland’s electricity export capacity to England and Wales from 3.3GW to nearly 7GW by 2021.
Iberdrola and Scottish Power chairman Ignacio Galan, said: “We are pleased to mark the start of construction on this hugely ambitious sub-sea electricity connection project.
“Our engineers are currently delivering some of the most important upgrades to the electricity network for more than half a century, with billions of pounds being invested and thousands of jobs being supported and created.
“We are planning a total investment in excess of £10bn by the end of the decade, with the majority on network upgrades and renewable energy projects.
“The Western Link project will act as a benchmark for similar developments around the world, as the deployment of this technology at such a large scale has never been undertaken before. This will help to increase energy security across the UK, and will benefit the people of Scotland, England and Wales.”