Germany's economy minister wants to cut the support price paid for electricity from solar and wind power generators by about a third by 2015, according to a draft proposal for one of the most challenging economic reforms facing Chancellor Angela Merkel's new government.

Under the draft proposal the feed-in tariffs paid to renewable power generators will be cut to an average across all technologies of 12 euro cents per kiloWatthour (cent/kWh) by 2015 from 17 cents/kWh currently.

And Economy Minister Sigmar Gabriel, who also leads the Social Democrats (SPD), wants the reduction to start taking effect for some new projects from as early as next week, according to the draft seen by Reuters on Saturday.

"The old rates of support (under the old renewable energy law (EEG)) are applicable for wind energy plants that start operating by Dec 31, 2014 and that were authorised ... by Jan. 22, 2014," said the draft outline prepared for a cabinet meeting this week.