UPDATE 1-Abengoa secures E.ON as partner for solar plants

* E.ON to pay for half of 550 mln euro investment

* Both companies to operate the two plants

* Building of the plants in Ecija has started already

* Abengoa, E.ON plan to further develop Solar power

(Adds quotes, joint dateline)

FRANKFURT/MADRID, Nov 25 (Reuters) - Spanish renewable energy company Abengoa (ABG.MC) will team up with German utility E.ON (EONGn.DE) to build two solar mirror plants in southern Spain, benefiting from E.ON's cash and large grid expertise.

E.ON will pay half of the overall investment of 550 million euros ($828 million) for the two plants, which have a capacity of 50 megawatts each, giving Seville-based Abengoa access to the finance power of the world's largest utility by sales, the companies said in a statement.

Spain has not yet released a list of solar mirror plants included in its new renewables register, which grants subsidies on normal electricity prices of about 27 eurocents per kilowatt hour, but the companies are confident the plants will be included.

"It is highly probable that they will be included in the register; I cannot say more at the moment," the head of Abengoa's solar division Santiago Seage said at a press conference in Madrid following the announcement.

Abengoa, which has already started building the two plants in Ecija, close to Seville and plans to start producing power in 2011 and 2012, respectively, with the power stations, said E.ON was not just a financial partner in the joint venture.

"E.ON will learn from us in the field of solar thermal energy, but we will learn from E.ON about large energy grids and plants," Seage said.

Both companies plan to extend the partnership to further develop solar power in Spain and will study future projects on a case-by-case basis.

The plants use the sun to generate steam that powers turbines, a technology called solar-thermal as opposed to solar cells. (Reporting by Peter Dinkloh and Tom Kaeckenhoff in Frankfurt and Jonathan Gleave in Madrid; writing by Peter Dinkloh and Jonathan Gleave, editing by Will Waterman) ($1=.6643 Euro) ((peter.dinkloh@reuters.com; +4969 7565 1345; Reuters Messaging peter.dinkloh.reuters.com@reuters.net))