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The shortage of silicon, the key ingredient in solar panels, is being caused by demand far outstripping supply. Silicon is used in a number of technologies besides solar panels such as microprocessors for computers. As a semiconductor for tranmitting electricity it is extremely efficient, but is not so efficient at converting solar energy into electricity, only converting 12%, typically.

There are a number of emerging technologies such as polymer solar cells which are seeking to displace silicon. Compared to silicon-based devices, polymer solar cells are lightweight, disposable, cheap to make and flexible.

In the short-term however, reports suggest that the current silicon shortage will lead to a glut as producers seek to meet the demand, leading to lower prices for solar panels. Ultimately, because of the complexity of production, other cheaper materials will take silicon's place.

Plans to cut carbon dioxide emissions and meet more of Britain's energy needs by an expansion of offshore wind farms have had to be revised, because experts now believe the chances of building them before 2010 at the earliest is unlikely.

?There is a worldwide shortage of wind turbines,? said Dr Gordon Edge, director of economics and markets at the British Wind Energy Association, who claimed that a recent series of tax credits introduced in the US for the American wind power industry had sparked a construction boom.

?The US industry is going hell for leather at the moment and relying on imports of wind turbines from Europe. All new projects are having to negotiate a long time in advance. People are ordering turbines now for delivery in 2009 and smaller players with not so much market power are losing out even more. Globally, it's going to take two or three years for us to catch up with demand.?

There are now 1,866 turbines in operation at 148 sites in the UK, with an additional 352 sites either under construction or planned. For many rural communities in Scotland and the rest of the UK, wind farms have long been seen as a potential economic boom and several small communities have set up their own projects, but shortages may threaten them.

?A lot of the turbine manufacturers won't even talk to small community projects looking for just one, two or three turbines,? said Ian McLean, of Renewable Devices Energy Solutions, an Edinburgh-based company that has been involved in the development of about a dozen small wind farms.