Energy giant Scottish & Southern Energy today ramped up its renewable energy target for the next five years.

The Perth-based group said it was now aiming to generate 4000 megawatts (MW) of green energy from windfarms, hydro-electricity and bio-mass plants by 2013, up from 3500MW previously forecast.

The new target is double SSE's current renewable output, and equivalent to around 7% of the UK's electricity needs.

It comes after SSE under-estimated previous development capacity following the £1.1 billion acquisition of wind farm developer Airtricity, which was agreed earlier this year.

But the Southern Electric, Scottish Hydro Electric and Swalec operator said it was also looking for a potential new hydro electric plant in the Scottish Highlands.

The 4000MW goal - which SSE warned was subject to projects securing all of the approvals in a "timely" manner - comprises 1500MW from hydro-electric plants, 2250MW of on and off-shore windfarms, and 250MW from bio-mass generation.

Windfarm schemes in the pipeline include a 483MW scheme in the south of Scotland, and a proposed 504MW site off East Anglia. A 100MW hydro-electric plant at Glendoe near Loch Ness is also due to come on stream this year.

SSE has pledged to spend £2.5 billion on capital investment for its renewable energy schemes over the five year period.

Announcing the target, the firm also said its green generation capacity passed the 2000MW mark this month.

Among its existing renewable power sites are the 120MW windfarm at Hadyard Hill in South Ayrshire, and a 215MW hydro plant at Tummel Valley in Perth and Kinross.

It also operates gas-fired stations, including one at Peterhead in Aberdeenshire, and a coal-fired plant at Ferrybridge in West Yorkshire. SSE's total electricity generation is 10,000MW.

Chief executive Ian Marchant said the group's aim for 2013 was "realistic and achievable", but also subject to the UK's policy and planning framework.

He added: "The logic for renewable energy is compelling and we have the commitment and financial strength to realise the opportunities that will flow from it - opportunities that were materially enhanced by the acquisition of Airtricity."

As well as power generation, SSE also supplies household energy in the UK and last week announced price hikes of up to 15.8% for gas and electricity customers. It was the last of the "big six" suppliers to hike bills this year amid soaring wholesale energy costs.

SSE's energy plans are in tandem with EU demands for 20% of electricity to be derived from renewable sources by 2020.

The group is currently trying to secure planning permission for a controversial pylon line upgrade through some of the most picturesque countryside in Scotland.

SSE says the 137-mile Beauly-Denny line, which would see giant pylons erected through parts of the Cairngorms and the southern Highlands, will help transmit renewable energy from the north of Scotland to the UK national grid.

The project has been the subject of a long-running inquiry the outcome of which will be decided upon by Scottish ministers this year.