Prince Charles on Friday commended the efforts of Teri Energy and Resources Institute for coming out with energy efficient technologies.

"These achievements are all the more important in a nation where more than 16 per cent of the world's population has to be supported from the resources of about 2.5 per cent of world's surface," Charles said in his address at the 'TERI Retreat' in Gurgaon, Haryana.

The prince also expressed interest in the Underground Earth Tunnels installed at the institute, which insulate buildings by keeping them cool in summers and warm in winters.

The concept is based on the observation that underground cellars are usually cooler in summer and warmer in winter.

Four tunnels each 70 metres long and with a diameter of 70 cm have been laid at a depth of 4 m below the ground in the building.

Charles said energy efficiency in buildings is a prime example of how a "problem shared can be a problem halved".