The £50 million (EUR57 million) deal will see Repsol partner its Iberian neighbour EDP Renovaveis to develop two of the three sites. Repsol will have a 33% stake in the 1.5GW Moray Firth site and a 51% stake in the 905MW Inch Cape site off the coast of Angus.
It has also acquired 25% of the 920MW Beatrice site in the Moray Firth to be developed jointly with SSE Renewables.
Spanish gas and electricity group Gas Natural Fenosa, in which Repsol is a major shareholder, will buy half of SERL if UK regulators give approval. Repsol spokesman Kristian Rix told Windpower Monthly that a final decision would be made "within weeks".
An agreement of lease with the UK Crown Estate for SERL to develop the Inch Cape site under the Scottish Territorial Waters Leasing Programme was announced at the same time as the company's sale.
EDP and SeaEnergy were awarded acreage by the Crown Estate in January 2010 to develop the Moray Firth site, in the UK Round 3 offshore wind leasing programme.
In February 2009 SSE Renewables and SeaEnergy were awarded exclusivity to develop the Beatrice site.
Repsol's decision to follow Norwegian Statoil's example in transferring offshore experience in oil and gas extraction into offshore wind energy is an adventurous but premeditated move.
In April 2010 the group created a specific renewables division called Repsol Nuevas Energias "to identify opportunities and promote projects" in biofuels and renewable energy. In September last year it acquired a 47% stake in the windpower developer Orisol, which has 1.9GW of projects in Spain, Italy and the US. Repsol's acquisition of SERL itself is carefully targeted - it was created specifically by parent company Ramco (now SeaEnergy) to transfer experience acquired in oil and gas operations in the Caspian basin to offshore wind power in Scotland.
The Scottish offshore venture is "a learning experience to evaluate when and where we do things," says Rix, although he adds that Repsol already has "the ability to manage complex offshore projects in terms of logistics, of manning installations offshore and of anchoring things to the seabed".
While the UK offers the biggest opportunity at present, Rix does not discount future offshore involvement elsewhere. Options in Spain are limited, however, by adverse topography and by the much-reduced targets in the government's latest renewable energy plan, published in May.
Meanwhile, SERL's parent company SeaEnergy will continue, focusing on its offshore marine services business, SeaEnergy Marine.