A new target to generate the equivalent of half of Scotland's electricity needs from renewable energy by 2015 has been set by the first minister.
Alex Salmond revealed the target at the RenewableUK conference in Glasgow.
The SNP claimed the new goal was achievable, after the government confirmed Scotland had beaten a 31% target for 2011 by about 4%.
But the Scottish Greens warned that without ending the use of fossil fuels the long-term targets would not be met.
The first minister told delegates the renewables industry presented a "massive economic opportunity".
He said the new target would help build on the current 11,000 jobs in green energy following a "bumper year" for investment, with projects estimated to be worth £2.3bn.
Investment in jobs
The Scottish government's new interim target for 2015 is contained in a refreshed Routemap for Renewable Energy for Scotland.
According to figures published in July by the UK Department for Energy and Climate Change, the period between April 2011 and June 2012 saw £2.3bn of investment announced in Scotland on green projects. SNP ministers hope that will create up to 4,500 jobs.
Earlier this year, the Scottish government confirmed Scotland had beaten its 2011 target on renewable energy.
Official figures revealed that about 35% of Scotland's electricity demand was met by green energy - beating the target of 31% set in 2007.
Mr Salmond told the conference: "When I became first minister in 2007, I inherited a target for 50% of Scotland's electricity to be produced by renewable sources by 2020.
"We now know that we can achieve much more than that, more quickly - having already exceeded our 2011 target.
"Last year, we published a Routemap for Renewable Energy for Scotland, outlining how we would meet the equivalent of 100% of Scotland's electricity demand from renewable sources by 2020.
"Today, we are publishing an update to that Routemap. It shows clearly the progress that has been made in the last year.
"In the light of that progress, I can announce that we have set a new interim target - by 2015, the equivalent of 50% of Scotland's electricity demand will be met by renewable sources.
"This target is ambitious, but also achievable. It is based on current data about capacity which is operational, under construction, or has been consented."
But last week the Scottish government was attacked for failing to meet its own climate change targets in 2010, according to the latest official figures.
They showed greenhouse gas emissions rose by 1.9% on 2009 figures, after taking emissions trading into account.
At Holyrood, Environment Minister Paul Wheelhouse blamed "exceptional cold snaps" among other factors for missing the target. But opposition politicians said the SNP had resorted to blaming the weather instead of their record on climate change.
Responding to the announcement of the new target, Scottish Green co-convener Patrick Harvie said: "50% by 2015 is clearly achievable but the most important target is the long-term reduction in greenhouse gas emissions.
"Renewable energy will help us to get there but only if we reduce fossil fuel consumption at the same time, sadly something the SNP are less keen on."
Scottish Conservative MSP Murdo Fraser, convener of the Holyrood energy committee, said: "The biggest problem with the SNP's renewable energy target is that it's completely underpinned by wind power.
"Not only is that an unreliable and intermittent source, but it's led to turbines blighting communities across the whole country."
WWF Scotland said it was vital to match the progress made with similar ambition to improve energy efficiency in homes and tackle emissions from transport.