Solon says it recorded a €52m ($74.7m) write-down in the second quarter on its SilPro investment, after predicting a €40m hit back in April.
SilPro, based in Saint Auban, has been in administration since April 2009. Solon blames the collapse of SilPro on the financial climate, which prevented the firm from getting loans.
Solon was linked to SilPro through its 48% stake in SOL Holdings, which it established with now-bankrupt Dutch renewables firm Econcern.
