Solar energy greener when home grown

Solar panels manufactured overseas can have twice the carbon footprint of those produced domestically, a new life cycle analysis (LCA) of photovoltaics has shown.

So far, similar LCAs have focused on Europe or North America – where the use of solar energy is highest and the majority of R&D is concentrated – and assumed that the materials are manufactured in-country. But in reality 80% of silicon-based photovoltaics are manufactured in Asia, where there may be fewer environmental controls. To investigate the impact of this, a team led by Fengqi You at Northwestern University, US, carried out LCAs for photovoltaic modules under two different scenarios: those that are manufactured and installed in Europe, and those that are manufactured in China, then transported to Europe and installed.

The energy payback time – a measure of the time it takes the modules to generate the energy required to make them – rose from 1.6 to 2.3 years for multi-silicon photovoltaics when manufactured in China. Their carbon footprint more than doubled – 69.2 CO₂ equivalents/kWh compared with 31.8 CO₂ equivalents/kWh for those made in Europe. The team say this is mainly due to the use of coal to generate electricity in China, as some parts of the manufacturing process – such as the production of purified silicon – have high electricity demands. They suggest this effect should be recognised in Europe and the US, and addressed with a carbon tax on imported photovoltaics.