Environmental boon or disaster in the making? (Image: F1 Online/Rex Features)

What could be greener than row upon row of rooftops covered with gleaming solar panels? Yet as the first generation of photovoltaic panels approach the end of their useful life, the prospect of these devices ending up in landfill threatens to tarnish their eco-friendly credentials.

Devices installed in the early 1990s will start reaching the end of their expected 25-year lifespan around 2015, as their ability to turn the sun’s rays into electricity fades. Many solar cells use toxic metals such as cadmium – or rare metals like indium, which will soon start running out – so recycling will be crucial.

A few solar companies are already offering their own recycling schemes. First Solar, based in Tempe, Arizona, offers to take back and recycle all the cadmium telluride thin-film solar cells it produces. And the industry-backed European association PV Cycle, based in Brussels in Belgium, is implementing a voluntary take-back and recycle programme that it hopes to have running by 2015.


Where should we place these centres? To help governments and companies plan large-scale recycling networks, Jun-Ki Choi and colleagues at the Brookhaven National Laboratory in Upton, New York, have developed a model that calculates how many centres each country or region should have, and where they should be located.

It is designed to keep down the cost of building the recycling facilities, and minimise the distance trucks have to travel to collect and transport the panels.

Solar cycle

Emissions from transporting the panels can make up a significant proportion of their overall carbon footprint, according to Pei Zhai and colleagues at Arizona State University in Tempe, who calculated the life-cycle emissions of solar panels.

Zhai’s calculations takes into account the production of machinery and gas used to make the panels, and the trucks used to transport them to their final installation site. They show that 32 grams of carbon dioxide is emitted for each kilowatt-hour of electricity generated by the latest solar cells.

This figure has halved over the last decade, as the industry has improved its manufacturing processes, and it is only a fraction of that emitted by coal, at over 300g/kWh.

The figure is nevertheless 60 per cent higher than previous estimates, which did not take into account factors such as transportation. If solar energy were to make up 10 per cent of the country’s electricity mix, this difference would add an extra 0.23 per cent to overall grid emissions in the US – a small but significant amount.

Solar cell makers have had their green credentials questioned in other respects, too. Waste produced during the manufacturing process contains mercury and chromium. And in 2008, newspaper reports suggested that toxic silicon tetrachloride produced during photovoltaic manufacture had been dumped onto Chinese farmland.

Journal references: Jun-Ki Choi’s paper: Environmental Science & Technology, DOI: 10.1021/es101710g; Pei Zhai’s paper: Environmental Science & Technology, DOI: 10.1021/es1026695

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