Some countries are finding it increasingly hard to transform their energy systems while maintaining good security of supply, the World Energy Council (WEC) says.

In the latest version of its Trilemma Index, which scores countries on their progress towards three key energy sector goals, WEC reports that it has placed additional countries on a negative watch list, while only two have achieved a triple A score.

WEC measures 130 countries on their approach to energy security, environmental stability and energy equity and says that some countries are struggling with the challenge of balancing the trilemma goals and financing the transformation of their energy systems.

Sweden and Switzerland have maintained their triple A status, while the UK has been downgraded from AAA to AAB, reflecting lower affordability of electricity. The US and South Africa have been added to WEC’s negative watch list, which already consists of Germany, Italy, Japan and the UK, reflecting concerns over energy security.

The Trilemma report will help countries to map out a sustainable course for their electricity systems, said WEC. "For countries to move up in the rankings and remain ahead of the pack, they must adopt prudent, forward-looking energy policies to meet decarbonisation goals and maintain competitiveness," said Joan MacNaughton, Executive Chair of the World Energy Trilemma study.

The report’s findings show that the best-performing nations tend to be developed countries with higher shares of energy coming from low- or zero-carbon energy sources supported by well-established energy efficiency programmes.

MacNaughton added: "The $48-53 trillion needed for investment in global energy infrastructure is increasingly contingent on a clear climate framework and a global target for emissions. It is clear that the energy industry has embraced the sustainability agenda and is working to help curb greenhouse gas emissions.

"It has an important role to play in achieving a successful energy transition, but key actions are required by countries if the full potential of the energy sector is to be realised."