June 2: NorNed cable benefits mainly coal plants
Long distance submarine power cables, like the NorNed cable between Norway and the Netherlands, can buffer renewable power across Europe. At the moment though, it's mainly coal power that benefits from it.
Near Feda, at the Fedafjord in Norway, the Norwegian transmission system operator StatNett has built a station to convert 450 kilovolt DC power from the NorNed cable into 300 kilovolt Norwegian grid. This is the point where power exchange between the Dutch and the Norwegian grid takes place.

The DC-AC converter station near Feda

The 580 kilometre long NorNed cable between Eemshaven (Netherlands) and Feda is the world's longest submarine power cable. It has a power capacity of 700 megawatts – comparable to a medium sized power station – and it was budgetted at 550 million euros. It has been in operation since 5 May 2008. In the first two months of its operation, it generated 50 million euros of income from power companies that rented the facility. Extrapolation learns that the cable could be payed for in two years, instead of the nine years that were originally estimated.
The NorNed is not the first submarine power connection to Norway. Denmark has installed three high voltage direct current (HVDC) power lines from Tjele (Denmark) to Kristiansand (Norway). These Skagerak lines, the first one originating from 1977, were designed to buffer the substantial share of wind power (20 percent in 2009) in Denmark.
Overproduction of wind power may be exported to Norway, where hydro power production could then be reduced, or water pumped into mountain lakes to buffer energy for later use (so-called 'pumped hydro'). Conversely, hydro power from Norway may be imported in case the national power plants don't meet the demand.

A small tunnel connects the two turbine halls of the Tonstad hydro power plant

Other submarine cables are planned between Germany and Norway (Nord.Link) and between the United Kingdom and The Netherlands.
Interconnections like these are a consequence of European treaties to stimulate an internal market and free movement of people, goods and capital. The cables should strengthen the European grid, serve the European power market, connect renewable sources as well as reinforce security of supply.
But NorNed also offers an opportunity of power laundring, a electrical green-wash if you will, where cheap coal power from Holland at night is used to pump up water in Norway and resold later as renewable hydro power.
“I don't like you using that word”, reacts Georg Hamm from the Sira Kvina hydro power plant in Tonstad, some 60 kilometres north of Feda. “I'm not sure what the European regulations are on this.”
“The Tonstad power plant may not be the biggest in Norway, but it is the most productive”, Hamm says, “because we always have enough water to drive the turbines.” The NorNed cable only adds to the productivity. The plant operates two turbines 800 metres inside a granite mountain at a lakeside, totalling about 700 megawatts.

Georg Hamm

At the day of our visit, one of the turbines is being overhauled, allowing us a glimpse at the colossal machinery that normally lies hidden beneath the tiled floor. The other turbine operates at full power, making the concrete floor vibrate. “This is what 320 megawatts feels like”, muses Hamm.
As a Tennet (the Dutch grid operator) film on the NorNed cable explains, coal power from the Netherlands is exported to Norway in the night and hydro power from Norway is imported during daytime.
Although that may seem like power-laundring, Hamm explains this is only part of the game. In spring there is an overproduction of hydro power in Norway that gets exported via, amongst others, the NorNed cable. Also, he adds, buffering coal power allows Dutch coal plants to produce more efficiently. Exchanging coal to hydro power is marginal in the total use of the cable, he says. No figures provided.
The buffering of coal power overproduction from Holland may also be a temporary event (although apparently a highly profitable one) because of the low installed base of Dutch offshore wind (about 200 mw). As offshore capacity increases to the intended 6,000 megawatt, renewable power will need substantial buffering as well.
Additional measures will probably be needed to prioritise renewable energy over fossil power on the NorNed cable if the facility is to contribute to a more sustainable energy system in Europe.