Analysis: Renewables - but what kind?
How the UK might meet its renewable energy obligations.
The European Commission has presented the UK with two tough climate change targets: to increase its use of renewable energy more than sevenfold to 15 per cent of all energy consumption by 2020, and to cut greenhouse gas emissions by 16 per cent by the same deadline.
Each European Union member state will have to make a specified contribution towards the EU-wide targets of cutting greenhouse gas emissions by 20 per cent by 2020, and boosting the use of renewable energy to 20 per cent.
The Commission, the EU's 'civil service', developed the energy and climate change package for approval by the Council (representing member governments) and the Parliament. It will be the subject of detailed negotiations before a final text is agreed.
UK Environment Secretary Hilary Benn said the proposals sent a clear signal to the world that Europe was taking decisive action to fight climate change: "This plan shows exactly what we are aiming for globally - a comprehensive and effective agreement to tackle climate change, with the carbon market at its heart."
But how is the UK going to meet these bold targets?
The UK may not have sunshine on its side as far as large-scale power generation goes, but our soggy islands have plenty of scope for harnessing the power of water.
Hydropower - mostly large-scale dams in Scotland - currently supplies the greatest proportion of renewable electricity, delivering some 4,605GWh in 2006, or about 40 per cent of total generation from renewable sources.
And while a massive expansion of wind power is expected, industry experts believe hydro can still have a role to play as a well-established conventional energy source.
The Scottish Government and the Department for Business are currently funding reviews into what extra capacity hydropower generation can supply, but British Hydropower Association (HPA) chief executive David Williams estimates there is another 2GW to 3GW that could be exploited - equivalent to the total capacity of our existing wind farms.
Most of the potential would be projects with generating capacity of less than 20MW and would not involve dams but would be 'run of river' schemes diverting water through turbines. Microgeneration water schemes could also contribute a small part.
Even with wind capacity increasing, it is estimated that almost 30 per cent of renewable electricity will be coming from hydropower in 2010; a mix which Williams believes provides a stability of supply. Hydropower is less intermittent than wind, and more predictable.
Scientists and energy providers are also looking offshore to the power of waves and tides to generate electricity.
There are two ways that tides can be harnessed for power - tidal stream, which draws energy from fast-flowing currents, and tidal range, which exploits the difference in water height between tides.
Together it is estimated that the two resources could supply at least 10 per cent of the UK's electricity if fully exploited - about 5 per cent each. But the most high-profile proposal for a tidal range project is also highly controversial: a barrage across the Severn Estuary which could alone generate about 4.4 per cent of UK electricity supplies.
The Severn Barrage - with an estimated cost of some £15bn - could generate large quantities of low-carbon electricity for 120 years but would destroy some 11,000 hectares of natural habitat in the estuary.
Last October the government said it would carry out a multi-million pound feasibility study into a barrage. The Sustainable Development Commission declared its support for the idea just days later, tempered by a warning that any scheme must be a public project complying with environmental laws.
However, many environmentalists - who support renewable energy - are critical of the proposed barrage because of the threat it poses to wildlife.
Announcing further details of the Severn tidal power study, Business Secretary John Hutton said the potential scale of the project and the impact it could have on securing energy supplies and tackling climate change would be breathtaking.
The study will consider both tidal barrages and lagoons, and will analyse the potential environmental, social and economic impacts of projects.
Friends of the Earth has welcomed the examination of a tidal lagoon system in the estuary, which would generate electricity from tidal water captured in lagoons to flow through offshore turbines. FoE says this would be cheaper and less damaging than a barrage.
Another form of renewable power is wave technology, which can generate electricity in a number of ways - for example, through floating structures producing power through movement or through turbines driven by water.
While wave power is a technology in its infancy, with only a handful of demonstration projects up and running, UK waters have some of the best potential in the world.
While experts say the UK needs an energy mix from a number of different sources to ensure a secure supply, on the renewable front it is clear that wind will have to lead the way.
Hydropower is currently the largest source of renewable electricity, followed by landfill gas, but it is wind where the big expansion is planned, with the government earmarking it as the dominant source to meet the EU renewable energy targets.
Gordon Edge, director of economics and markets at the British Wind Energy Association, says that wind "is going to have to do the heavy lifting". "Wind is the only low-carbon source of energy that can deliver at scale in 10 to 15 years," Dr Edge commented.
But with just 8.2 per cent of overall energy from renewable coming from wind in 2006, there's a long way to go.
Operational wind farms currently account for just under 2GW of capacity onshore and less than half a gigawatt offshore. There is a further 1.5GW of capacity under construction on and offshore, and another 4.5GW which have been given the go-ahead.
In December, Hutton announced plans to open up the UK's seas to a potential 33GW of wind farms. That would require an extra 25GW of capacity on top of what is planned from offshore wind and 50 times the current operational level, and would see the installation of thousands of turbines around the coast.
If the sort of expansion being talked about goes ahead, wind could be providing more than a quarter of the UK's electricity by 2020.
It's an option the BWEA says is achievable, although there are obstacles such as planning and grid issues onshore and investment in the technology for offshore wind.
The main planning obstacle onshore comes from radar and aviation concerns. Offshore, plans are needed for the next generation of turbines which will have generating capacity of 7MW to 8MW, more than twice that of today's 3MW turbines.
But Edge said the UK is ideally placed to exploit its offshore wind capacity, not just because it is windy around our coasts, but because the nation has transferable skills from the offshore oil and gas industries.
And while wind still needs support to make it competitive, costs are coming down, turbine production can stimulate manufacturing industries and a 3GW turbine takes just over six months to pay back in clean energy the carbon used in its manufacture and installation, according to Edge.
Moreover, he pointed out, once the up front costs of building a wind farm have been met the energy input - wind - is free, so prices are more stable than sources dependent on fluctuating oil markets. "It's now clear that wind is never going to go away. Even in the US they have decided they're going for it, so people are investing," he said.
Before too long massed arrays of turning blades could change our seascapes forever.