The Dutch solar energy sector has called for more clarity about the source of its materials after an investigation revealed that some of the largest suppliers in China are suspected of using forced labour from the minority Uyghur population.

Research by the US-based Horizon Advisory found that the three largest solar panel producers in the world, all based in China, acquired their raw materials from the Xinjiang province, where up to a million people are detained in so-called re-education camps.

Three Dutch wholesalers, ESTA, SolarToday and ProfiNRG, whose customers include solar energy farms subsidised by the government, source panels from two of the Chinese companies, Jinko Solar and Trina Solar, the Financieele Dagblad reported on Thursday.

The companies said they were aware of the claims of forced labour in China. ‘If it is proven that this is really happening we will have to reconsider the position of a brand such as Jinko Solar,’ said Klaas Galama, CEO of ESTG.

The New York Times reported on Horizon Advisory’s findings in January, but there has been relatively little coverage in the Netherlands until now. A representative of the Chinese embassy in Washington dismissed the reports of forced labour as ‘a rumour created by a few anti-China media and organisations’.

A spokesman for Solarfields, one of the Netherlands’ largest solar energy farms, said it would investigate the allegations. ‘Honesty requires us to say that we had not thought about this in this way until now. We are carrying out a review of our value chain.’

Chinese solar panels are also sold in the Netherlands to private homeowners through online retailers such as Coolblue or via collective solar schemes by organisations such as Vereniging Eigen Huis. A VEH spokesman said it was aware of the problem but unable to verify the reports of forced labour.

Representatives of the sector also warned that China is so dominant in the solar energy sector that it would be impossible to meet the Netherlands’ renewable targets without Chinese imports.

‘At least 80% of solar panels in the Netherlands come from China, but the other 20% are also partly made in China,’ said Amelie Veenstra, policy director of sector organisation Holland Solar.