Sunday, February 8, 2009

Why sustainable power is unsustainable

Standard silicon solar cells are shiny and lustrous, but that means they waste energy (Image: stock.xchng)

Renewable energy needs to become a lot more renewable – a theme that emerged at the Financial Times Energy Conference in London this week.

Although scientists are agreed that we must cut carbon emissions from transport and electricity generation to prevent the globe's climate becoming hotter, and more unpredictable, the most advanced "renewable" technologies are too often based upon non-renewable resources, attendees heard.

Supratik Guha of IBM told the conference that sales of silicon solar cells are booming, with 2008 being the first year that the silicon wafers for solar cells outstripped those used for microelectronic devices.

But although silicon is the most abundant element in the Earth's crust after oxygen, it makes relatively inefficient cells that struggle to compete with electricity generated from fossil fuels. And the most advanced solar-cell technologies rely on much rarer materials than silicon.

The efficiency of solar cells is measured as a percentage of light energy they convert to electricity. Silicon solar cells finally reached 25% in late December. But multi-junction solar cells can achieve efficiencies greater than 40%.

Although touted as the future of solar power, those and most other multiple-junction cells owe their performance to the rare metal indium, which is far from abundant. There are fewer than 10 indium-containing minerals, and none present in significant deposits – in total the metal accounts for a paltry 0.25 parts per million of the Earth's crust.

Most of the rare and expensive element is used to manufacture LCD screens, an industry that has driven indium prices to $1000 per kilogram in recent years. Estimates that did not factor in an explosion in indium-containing solar panels reckon we have only a 10 year supply of it left.

If power from the Sun is to become a major source of electricity, solar panels would have to cover huge areas, making an alternative to indium essential.

Why sustainable power is unsustainable

No comments: