Saudi Arabia, the world’s biggest oil producer, has plans to become 100% powered by renewable and low-carbon forms of energy, according to an influential member of the royal family.

But the process is likely to take decades, and some observers are sceptical as to whether it is any more than window-dressing.

Prince Turki Al Faisal Al Saud, founder of the King Faisal Foundation and one of the state’s top spokesmen, told the Global Economic Symposium in Brazil that he hoped the kingdom might be powered entirely by low-carbon energy within his lifetime – he is 67 – but that he thought it was likely to take longer.

However, he insisted Saudi was moving ahead with investment in renewable energy, nuclear power and other alternatives to fossil fuels and that it could use its vast oil reserves for other goods, such as plastics and polymers.

‘Oil is more precious for us underground than as a fuel source,