In a letter to Prime Minister Manmohan Singh, the MPs said, "What we gather is that the solar scam in Kerala is just a tip of the iceberg. So far, the state government and its police could not get into the details and the core of this scam.
"We demand that the Centre should hold an independent and thorough probe into this issue using federal agencies."
The letter, signed by K N Balagopal, P Rajeeve, M B Rajesh and P K Biju, said, "If we look into the grid connected schemes, the corruption may be much bigger. It may end up as corruption scandal such as the 2G or the coal scam, which will result in the loss of several thousands of crore to the exchequer."
The CPI(M)-led Left Democratic Front (LDF) in Kerala had last month carried out a two-day siege of the state secretariat after the Congress-led state government agreed for a judicial probe into the solar scam.
The MPs also claimed in the letter that fraudulent companies had cheated hundreds of investors "allegedly with the help of the highest offices in the state".
"These companies are grabbing money from both the innocent consumers and the government. In fact, the government is helping these private players to maximise their profit using its own schemes," they said.