Michael McCarthy: We need every megawatt the sea breeze has to offer

A new British seascape is on the way, because of the fight against climate change. Once it was ships' sails we saw on Britain's maritime horizon. Then, for a century or so, it was the funnels of steamships. But, in the century to come, it will be windmills.

Increasingly, whenever we look out to sea from our coastline, the turning blades of wind turbines will be visible in the distance, glinting in the sun as they revolve. For offshore wind power is likely to take the lead as the main generating source in Britain's renewable energy sector, probably within the next 10 years.

Putting wind turbines in the sea is technically more difficult than siting them on land, and more expensive – at between £1.5m to £2m per megawatt of generating capacity installed, it costs perhaps twice as much. But an offshore wind farm has several major advantages that its onshore equivalent does not possess. Firstly, it is much less likely to get caught up in the planning process before construction, as there is no one living near by to object (the amount of onshore capacity that is held up in the planning system is about four times greater than the amount that is actually installed).

Secondly, the "wind resource" – the amount of wind that actually blows for a given amount of time – islikely to be much greater out at sea than on land.

And thirdly – and this is perhaps the most important consideration – the whole project can be very much bigger. In fact, it can be gigantic.

Take the London Array, potentially the world's biggest wind farm, likely to get under construction soon. It will consist of 270 turbines generating about a gigawatt (a thousand megawatts) of electricity – as much as a large coal-fired power station. But there is nowhere at all in southern England, or perhaps even in England as a whole, or perhaps even in all of Britain, where such a gigantic project could be accommodated – so it is being located in the middle of the Thames Estuary.

This ability of offshore wind farms to be so big will shape the whole development of wind power in the UK, because at some point, some sort of limit will be reached to the number of wind turbines than can be accommodated on land – but at sea, that limit is likely to be very much further away.

At present, the installed capacity of onshore wind in Britain totals about 2,000 megawatts, compared to about 300 megawatts of wind offshore. But before too long, those positions will be reversed. By 2020, the British Wind Energy Association, the industry's umbrella body, thinks there could be about 13,000 megawatts of generating capacity installed onshore – which would supply 10 per cent of Britain's electricity demand – but as much as 20,000 megawatts of capacity out at sea (supplying a further 17 per cent of our power).

Britain will need every megawatt of this if we are to meet our EU obligation to supply 20 per cent of our energy from renewable sources by 2020. So expect a further mass sprouting of turbines over the hills – but even more, over the waves.