A short answer from a GE engineer to "Why are wind turbines so big these days?"
The bigger the blades, the more wind energy can be captured. Also, the higher the tower, the stronger the wind (in most places). Both of these translate into more electricity generated.
The trade-offs can mostly be summarized as extra costs that offset the benefit of extra production:
Bigger blades and towers are more expensive to transport
The larger the component, the stronger it has to be to withstand the wind force. Therefore, more structural material needs to be used, increasing cost.
The larger, taller turbines are more expensive to install. Bigger cranes are needed to lift the components and larger foundations are needed to hold them in the ground.
The industry has trended over the years to bigger and bigger machines - with new, bigger models coming out every year. This trend has slowed recently (but not stopped) as some of the cost barriers have been reached. Turbine designers are working now on new designs to overcome some of these challenges: lighter, stronger blades made out of carbon fiber, for example; or blades that can be shipped in two pieces and then assembled on site.
The American Wind Energy Association (AWEA) website
www.awea.org is a great place to start an investigation into wind energy. It contains a lot of basic turbine information (
http://www.awea.org/faq/wwt_basics.html ) and has links to more in depth information.
There are also some links for educators (
http://www.awea.org/pubs/documents/TeachersGuide.pdf )
