The flotation is being closely watched by investors and the industry for insight into the standalone market value of ailing coal and gas fired power stations and trading activities.

E.ON said in late 2014 it would pool and list its struggling power plants and volatile trading business, hoping this would free up enough cash for future investments, and give a boost to its renewable and grid business which it is now focussed on.

There will be no advance price range released for Uniper shares, but an expected dividend yield of 5 percent suggests an opening price of 11 euros and a market capitalisation of about 4 billion, a person familiar with the spin-off said.

Since the spin-off announcement, shares in E.ON have fallen by 43 percent, with investors pointing to substantial liabilities in relation to the storage of Germany's nuclear waste, which will remain with the company.

"The new energy world is so vastly different from the traditional one that they need completely different entrepreneurial strategies," E.ON Chief Executive Johannes Teyssen said.

E.ON shareholders will receive one Uniper share for every 10 E.ON shares they hold. E.ON will spin off 53.35 percent in Uniper in a first step and has previously said it does not plan to divest additional stakes before 2018.

In response to the crisis in conventional energy generation, caused by overcapacity and a rise in renewable capacity, Uniper plans to cut about 500 million euros in costs and sell at least 2 billion euros of assets.

(Editing by Maria Sheahan and Alexander Smith)

By Christoph Steitz and Arno Schuetze