Zephyr Investments Ltd completed its first investment in wind farms in April 2004. A second group of wind farms was contributed to Zephyr in December 2005, with a third group contributed in December 2006. Zephyr was the first off-balance sheet portfolio financing of wind farms operating under the UK Renewables Obligation Certificates ("ROCs") mechanism. RWE provided Zephyr with a long term fixed price power purchase agreement, including ROCs, and a long term operation and maintenance services contract for the assets. The Zephyr portfolio comprised 391 MW of mostly onshore capacity across the UK.

In May 2007, Zephyr was sold to a consortium of JP Morgan’s infrastructure fund and the Prudential.