MUMBAI (Reuters) - Four Indian renewable power producers are planning to raise up to $2.5 billion via dollar bonds offshore because of caution among domestic lenders, banking sources said.

In addition to the four solar and wind power firms, a fifth company that invests in renewable projects, Adani Group, has raised $250 million via a loan but has yet to publicly announce the borrowing, the sources told Reuters.

A source working with one of the bond issues said foreign borrowing was attractive because state banks were reluctant to lend due to existing bad loans to the power sector, while domestic banks worried about falling tariffs for solar power.

Foreign investors have been attracted to the sector by India’s commitment to expand renewable power capacity, with plans to invest close to $150 billion to meet its 2022 targets, analysts and bankers said.

New York-listed Azure Power Global Ltd AZRE.N, which has projects in the states of Rajasthan, Punjab and elsewhere, planned to raise $500 million via a dollar issuance, two bankers said.

Continuum Energy, a firm backed by U.S. bank Morgan Stanley that has projects in the southern state of Tamil Nadu and western state of Gujarat, planned to raise $400 million, the two bankers added.

Wind and solar power firm Greenko Group GRNKF.PK, backed by Singapore sovereign wealth fund GIC and Abu Dhabi Investment Authority (ADIA), planned a $1 billion issuance to refinance a dollar bond raised three years ago, three bankers said.

IL&FS Energy, which has thermal and solar power projects, was considering a dollar bond issue worth $500 million, said a source with knowledge of the deal but not involved in the process.

The fifth firm, Adani Group, which is controlled by billionaire Gautam Adani, has already raised $250 million via an offshore loan to invest in its solar power project in Karnataka, one of the bankers said.

The companies did not immediately respond to requests for comment.

Solar tariffs hit a new low in May when SBG Cleantech, which has SoftBank Chairman Masayoshi Son as one of its promoters, bid 2.44 per unit for building a solar park in the western state of Rajasthan.

Solar power players bid for the right to build projects on parcels of land that are set aside by the government. The player agreeing to sell the power it generates at the lowest price per kilowatt hour, are leased the land at a nominal price.

Despite the decline in tariffs, overseas investors scouting for higher yields are keen on such dollar bond issues, the bankers said, adding many were drawn by Indian Prime Minister Narendra Modi’s commitment to boosting renewable power output.

India, a signatory to the Paris climate accord, has an ambitious plan to raise renewable energy capacity to 175 gigawatts (GW) by 2022 from a current capacity of 57 GW.

Abhishek Tyagi, senior analyst at Moody’s, said India would have to invest “close to $150 billion to meet its 2022 renewable energy targets”, adding much of that was expected to come from foreign financing due to constraints among domestic lenders.