The company makes money from selling the leases, which are owned by investors who put up the money to finance the installation and subsequent monitoring and maintenance work.
And a report prepared by France's finance ministry criticised SocGen's procedures for monitoring its trades, adding to the pressure on Daniel Bouton, the bank's chairman, to step down.
At different times throughout the year, government departments examine their own spending in what are called monitoring rounds when unspent money is returned to the Department of Finance and Personnel (DFP).