Britain may choose not to buy electricity from an independent Scottish state if prices are higher than imports from other neighbours, the British government has said.
The comments were seen as another warning shot at Scotland five months ahead of its independence vote.
An independent Scotland would have to rely on electricity exports to Britain to sell excess renewable energy generation because its grid is only connected with England and, to a lesser extent, Ireland.
"With a range of generation sources within its own borders and elsewhere, a continuing UK would not be obliged to purchase energy from an independent Scottish state," Britain's Department of Energy and Climate Change said.
Britain also imports electricity from the Netherlands, France and Ireland and is planning to build other links to Belgium, Norway and Denmark.
Scotland's electricity network is connected with England, where the bulk of its excess electricity supplies are delivered. A smaller cable to Ireland is rarely used for export.
Companies producing electricity in Scotland include Iberdrola's Scottish Power and British utility SSE.
The government's warning that it may not want to buy Scottish electricity is its latest attempt to persuade Scottish voters to remain in Britain.
Scottish nationalists are arguing that a split would give them greater economic freedom.
Scotland votes on September 18 whether to end its 307-year union with England.