This is one stage of integrating Europe and Northern Africa into one large grid. Spain has excellent wind and solar resources and has done a very good job of installing wind turbines and solar panels. This new line will let Spain sell some of their clean power into the rest of Europe, letting Europe cut back on their use of fossil fuels.

It’s working….

The Edison/DC and Tesla/AC is correct. But from there on…

DC is less lossy over longer distances. There is a small loss at each end (~0.75%) in the conversion process so over shorter distances AC is used.

Early HVDC systems used mercury arc rectifiers, which were unreliable. Today almost all HVDC systems use thyristor valves.

The world is kind of full of HVDC transmission lines. The oldest still operating were built in the 1960s.

In the US we’ve got the Pacific Intertie which runs between the Pacific Northwest and SoCal, the Intermountain Intertie between Utah and SoCal, the Neptune between Long Island and New Jersey, ….

Here’s a list of HVDC lines.

http://en.wikipedia.org/wiki/List_of_HVDC_projects

Here’s a pretty thorough piece on HVDC transmission…

http://en.wikipedia.org/wiki/High-voltage_direct_current

AC does NOT have huge losses over distance, that’s why it is used. One of the main advantages of AC is that it’s easier to step up and down in voltage using relatively low tech transformers. Long distance AC lines run as high as 500kV (that’s 1/2 a million volts) and can easily be stepped down to residential voltages. The higher the voltage the lower the current in the wires and as a result the lower the line losses.

You can’t use transformers to step up/down with DC so creating the high voltages necessary for long distance transmission and stepping it down for local use is simply much more expensive. Up until now they’ve only been used for underwater systems where AC isn’t suitable.