2014 marked the turning point: the benefits linked to solar energy generation now outweigh the environmental costs of manufacturing the panels
Producing a solar panel requires energy: silicon, the key element in this technology, is melted in electric furnaces that, in most cases, are powered by fossil fuels. How sustainable is it to use technologies that produce no pollution during their lifetime, but whose manufacturing involves processes that can hardly be described as "sustainable"? Wilfried van Sark, of Utrecht University in the Netherlands, and his colleagues set out to find an answer. Here it is: in 2014 we reached the break-even point — the benefits derived from solar energy generation have outweighed the negative effects associated with manufacturing the panels.
Because of the amount of energy needed to produce it, a newly installed solar panel carries a "carbon debt" that it must pay off over the course of its lifetime. In other words, in its early life, a conventional solar panel is still part of the pollution problem rather than the solution. This aspect has not been lost on sceptics, who have gone so far as to claim that solar panels are not a viable alternative to fossil fuels. But the data tell a different story. Wilfried van Sark and colleagues have produced a detailed analysis published in Nature Communications. Drawing on dozens of studies, the research group calculated the energy required to manufacture all the solar panels installed worldwide between 1975 and 2015, and the carbon dioxide emissions associated with their production. They then examined the clean energy that all those panels have delivered since installation, and the corresponding amount of carbon dioxide avoided.
Looking at the numbers, researchers at Utrecht University found that solar panels manufactured today are responsible, on average, for around 20 grams of carbon dioxide per kilowatt-hour produced over their lifetime, which is estimated at around 30 years. That figure is well below the 400–500 grams produced by solar panels sold commercially in 1975, now some forty years ago. The numbers show that the amount of time a solar panel needs to pay back its "initial debt" incurred during production has fallen from 20 years for the first panels ever made to two years or less for the latest generation of solar panels.
The team also found that every time global solar capacity doubles, the energy required to make a panel falls by around 12 per cent and, similarly, carbon dioxide emissions drop by 17–24 per cent. In other words, the more panels that come to market, the more efficient and less costly the production process becomes.
Compared with the early 1970s, the cost of a solar panel has fallen from around €75 to less than €1 per watt of installed capacity. The dramatic drop is due on the one hand to the economies of scale achieved in the sector, and on the other to technological and manufacturing innovations. Energy and material consumption has fallen, while the output per solar panel has increased. In other words, the "research shows that, despite the rapid growth in the number of solar panels, greenhouse gas emissions during production are more than offset by the clean electricity these panels produce. We passed the break-even point at the end of 2014," said Atse Louwen, a researcher at Utrecht University.
The photovoltaic capacity installed worldwide today reaches 300 gigawatts, equivalent to a surface area of around 1,800 square kilometres of solar panels. An area as large as 250,000 football pitches, which this year alone has supplied more than 370 terawatt-hours of electricity — around 1.5 per cent of total global electricity supply — something that "might not sound like much, but already represents a reduction of around 170 megatonnes of greenhouse gases. And the potential for growth remains enormous," said Van Sark.