Germany, France, Belgium, the Netherlands, Luxembourg, Denmark, Sweden and Ireland and the UK are all working on a Europe wide supergrid of renewable energy. One of the main problems with renewable energy is that it relies on a particular kind of weather (depending on the type of renewable energy used) to be effective and a supergrid would help prevent the unreliability of renewable energy by combining different sources. The countries involved are investing in high voltage direct current cables rather than alternating current cables, as less energy is lost over long distances using the direct current cables.
Only a couple of cables have been constructed so far – one between the UK and the Netherlands, and one between the UK and France. A cable between Ireland and England is also due to be operational by autumn 2012.
The image below is taken from the article by the Guardian (link below) and shows the existing and proposed cables.
The UK is currently in talks with Iceland about adding their geothermal energy to this European supergrid. The cables to reach Iceland would need to be 1000-1500 km in length, which would make them the longest in the world.
To me, this seems like a really good idea, as even though the start up costs are expensive, having a system linking different sources of renewable energy will help to keep energy prices stable and (hopefully) reduce the need for countries to depend on coal, oil and gas as a main energy source.