Chief Minister Oommen Chandy announced the extension of the Commission period after a cabinet meeting here.
The Commission, headed by retired Kerala High Court judge G Sivarajan, has been entrusted to examine whether government suffered any financial loss due to the alleged deals.
The Commission was set up in October 2013 for a period of six months and later extended to six months.
The case relates to duping of several persons by the two prime accused Saritha S Nair and Biju Radhakrishnan after promising to install solar power panels for them.
After the scam broke out, the opposition had demanded Chandy's resignation as the names of two of his personal staff had come up during the probe.
The CPI(M)-led LDF opposition had demanded a probe by a sitting judge of the High Court, which was turned down by the court, following which a former judge was appointed to head the Commission.