FRANKFURT (Reuters) - Margins at German energy group RWE's (>> RWE) gas-fired power plants were higher than expected in the first half, it said on Monday, helping it forecast full-year profits at the upper end of its outlook range.

Overcast, calm weather meant less wind and solar generation, so RWE's gas and coal-fired power plants were called into action more often rather than losing money on standby, conditions which Chief Executive Rolf Martin Schmitz said were "very profitable".

That helped the group raise first-half adjusted core earnings (EBITDA) by 7 percent to 3.21 billion euros ($3.8 billion), in line with the 3.19 billion average forecast in a Reuters poll of banks and brokerages.

Schmitz said the group's gas-fired power plants ran an average 1,000 full-load hours in the first half of 2017, twice as many as in the same period last year.

Shares in RWE, which focuses on conventional power generation and energy trading, were up 1.3 percent by 1025 GMT, hitting their highest in nearly two months and making them the best performers among German blue-chips <0#.GDAXI> so far this year.

The group last year carved out its better-performing assets in renewables, grids and retail, listing them as Innogy (>> Innogy SE), in which RWE retains a 76.8 percent.

Schmitz repeated this might be reduced at some point but added: "We are not under pressure to sell".

Sources told Reuters earlier this year that RWE was studying a possible swap of its Innogy stake for a minority position in French group Engie (>> Engie).

RWE said it expects 2017 adjusted core earnings at the upper end of its target range between 5.4 billion and 5.7 billion euros. It also sees adjusted net income at the upper end of its forecast range of 1 billion to 1.3 billion euros.

It raised its outlook for the European Power segment, which is now expected to significantly grow adjusted core earnings, having previously forecast a substantial decline.

RWE said it would also benefit from the sale of most of its 1,140 megawatt Littlebrook oil-fired power station in Britain to property investor Tritax Big Box REIT (>> Tritax Big Box REIT PLC), expected to be completed later this year.

(Editing by Susan Thomas and David Holmes)

By Christoph Steitz

Stocks treated in this article : Engie, RWE, Tritax Big Box REIT PLC, Innogy SE