The bank's president, Jens Weidmann, was left to issue a statement that he regarded the bond purchases as "tantamount to financing governments by printing banknotes".
Mr Sarkozy had been a spokesman for Mr Balladur, but a presidency statement said he "never exercised the slightest authority in the campaign financing".
SolarCity, which has said it plans to go public and has filed a confidential IPO registration statement, will install, own and maintain the solar arrays, financing the projects through debt-equity funds it taps to pay for panels for customers who lease their photovoltaic systems.