* Sells 51% stake in four wind farms * Stake corresponds to 439 megawatts of capacity * RWE will remain operator of farms (Recasts, adds details on deal, context) FRANKFURT, Dec 14 (Reuters) - RWE, Europe’s third-largest renewables company, agreed to sell onshore wind assets in Texas worth $600 million to Canada’s Algonquin Power & Utilities, freeing up more cash to expand its business in other clean energy areas. The sale of a 51% stake in four onshore wind farms -- two in operation and two under construction -- equates to 439 megawatts of capacity, RWE said, adding the deal was expected to close in the first quarter of 2021. “The transaction with Algonquin demonstrates the attractiveness of RWE’s portfolio in North America. The U.S. play a key role in RWE’s strategy to grow its renewables business and to become carbon neutral by 2040,” RWE said. In the United States, the group operates 25 onshore wind farms and has about 1 gigawatt (GW) under construction. The move gives RWE more financial fire power to expand its renewables portfolio to more than 13 GW by the end of 2022 via net investments of 5 billion euros ($6.1 billion). The group earlier this year rose 2 billion euros in a share sale. Even though selling a majority, RWE will remain the operator of the wind farms, a common way by utilities to monetise renewable assets, which are attracting large investor interest due to their fixed returns and carbon neutrality. ($1 = 0.8228 euros) (Reporting by Christoph Steitz; editing by Thomas Seythal)