SCENARIOS - Energy policy in the next German government

BERLIN/FRANKFURT (Reuters) - German Chancellor Angela Merkel is seeking re-election in a federal vote on September 27, and polls give her conservatives a lead over their coalition partners and traditional rivals, the Social Democrats (SPD).

Merkel hopes to form a coalition with the business friendly Free Democrats (FDP), and the latest surveys give her enough support for such a centre-right alliance.

However, other ruling partnerships are possible, including a second consecutive "grand coalition," grouping Merkel's conservatives -- her Christian Democrats (CDU) and the Bavarian Christian Social Union (CSU) -- and the SPD.

Below are the most likely coalition scenarios and how they would probably affect German energy policy:

CENTRE-RIGHT ALLIANCE (CDU/CSU and FDP)

NUCLEAR ENERGY - All three parties in a centre-right coalition see nuclear energy as a crucial part of the energy mix so long as renewables are unable to generate sufficient amounts of electricity to replace them. The three parties would look to extend the lives of the 17 nuclear plants deemed safe, doing away with the plans to phase them out by 2020. German energy companies would likely be forced to give the state a portion of any additional profits generated by a lifespan extension. Sal Oppenheim analyst Matthias Heck estimates that if RWE and E.ON were allowed to operate their nuclear plants 15 years longer and gave up 50 percent of new profits, the gains could total as much as 9 euros per share for RWE and 4.2 euros for E.ON.

RENEWABLES - The commitment to renewables in a centre-right coalition might not be as strong as it was under a government that included the SPD or Greens, but all three parties are committed to the long-term goal of raising the share of renewables in the energy mix.

CLIMATE CHANGE - A centre-right government would likely take a more pro-business approach, refusing to set speed limits on national motorways or taking steps that would hurt the German car industry. The parties support a successor to the Kyoto Protocol and EU goals to reduce CO2 emissions.

GRAND COALITION (CDU/CSU and SPD)

NUCLEAR ENERGY - The SPD is unlikely to budge on its nuclear phase-out plan as it has been a centre-piece of party policy and remains a key campaign plank. Merkel's CDU/CSU would nevertheless push for a softening of the phase-out law in coalition talks and over the next four years. A failure to extend the lifespan of Germany's nuclear plants would have a limited negative impact, if any, on the share prices of leading German energy firms like RWE and E.ON. There would also be clashes over the need to identify a final repository site for nuclear waste. Conservatives want it to be Gorleben in Lower Saxony while the SPD wants a diverse, longer, discourse which so far has gone nowhere.

RENEWABLES - The conservatives and SPD revised a law last year on subsidising renewable energies such as wind, solar power and biomass, securing support levels for at least six years but also creating greater fairness and balance. Germany now gets 15 percent of its electricity from renewable sources and its goal is 27 percent by 2020 and 45 percent by 2030. The SPD would likely push hard for new energies as part of its programmes to create alternatives to fossil fuels.

CLIMATE CHANGE - A grand coalition would continue pursuing Germany's goal of reducing CO2 by 40 percent by 2020 from 1990 levels. There would be conflicting views on coal generation. The conservatives are largely pro-coal and support CCS (carbon sequestration and storage) process technology. Despite reservations about coal, the SPD could ill-afford to risk losing thousands of coal-to-power station jobs in western Germany and in eastern brown coal mining areas as they are key voter bases. The SPD supports stricter speed limits on motorways but the CDU/CSU oppose this.

OTHER CONSTELLATIONS

The three other coalitions that are considered possible after the German election are a CDU/CSU partnership with the Greens, an SPD coalition with the FDP and Greens and, least likely, a CDU/CSU government with the FDP and Greens.

All these constellations would have trouble bridging differences on nuclear energy and the two variations that include both the FDP and Greens would be at loggerheads over how far to go on climate change and renewables policies that risked hurting German business.

(Reporting by Erik Kirschbaum, Peter Dinkloh and Vera Eckert; Editing by Charles Dick)