* Sale could happen via market, to single buyer -sources
* Uniper stake worth 2.83 bln euros at current market cap
* E.ON plans swift sale, but not before 2018 (Adds additional information, context on energy M&A)
By Christoph Steitz, Arno Schuetze and Alexander Hübner
FRANKFURT, May 30 (Reuters) - German energy group E.ON has hired Goldman Sachs to explore options for a sale of the group's remaining stake in Uniper, the power plant and trading business it spun off last year, two sources close to the matter said.
Following the listing of Uniper in September, E.ON kept a 46.65 percent stake - currently valued at about 2.83 billion euros ($3.16 billion) - and has said it aims to sell the rest soon but not before 2018 due to potentially negative tax effects.
A sale could happen in several ways, including an outright sale to a third party or placements on the market, the sources said, adding it was less likely that peers would want to acquire the stake due to Uniper's eclectic business structure.
E.ON's exploration of options is at an early stage and no deal is imminent, the sources said.
Uniper has a range of operations from hydroelectric, coal- and gas-fired plants to storage assets and trading floors, and holds stakes in gas pipelines, LNG terminals and nuclear plants across Europe.
"Most power firms would want a part of Uniper, but there is hardly anyone with a profile that would accommodate all of the group's activities," one of the sources said.
Ever since their restructuring moves last year, German power firms are back on the M&A radar, with RWE exploring an asset swap with Engie involving its majority stake in Innogy.
One source said E.ON's Uniper stake could draw interest from private equity groups with a track record in the energy industry, including KKR, which in January agreed to buy assets from U.S. oil and gas producer SM Energy Co for $800 million.
This was one of a number of recent private equity-backed deals in the energy sector, which included Carlyle-backed Neptune Oil & Gas buying a stake Engie's exploration and production business for $3.9 billion.
E.ON, Goldman Sachs and KKR all declined to comment. ($1 = 0.8951 euros) (Editing by Georgina Prodhan and David Evans)