Europe has big plans for greatly expanding its renewable energy sources, but there’s a problem: weak connections between a patchwork of national power grids. The situation is particularly problematic for wind power, because smaller, isolated grids have more difficulty absorbing the variable power generated by wind farms.

Last month a Dublin-based wind-farm developer, Airtricity, and Swiss engineering giant ABB began promoting a bold solution to the continent’s power grid bottlenecks: a European subsea supergrid running from Spain to the Baltic Sea, in which high-voltage DC power lines link national grids and deliver power from offshore wind farms. When the wind is blowing over a wind farm on the supergrid, the neighboring cables would carry its power where most needed. When the farms are still, the cables will serve a second role: opening up Europe’s power markets to efficient energy trading.

The result would be a more integrated and thus more competitive European market, delivering power at lower prices. And it would enable Europe’s grid to safely accommodate even more clean, but highly variable wind power. That accommodation will be needed because the European Union has set a target of 21 percent of electricity from renewable sources by 2010, and much of this will come from wind farms. “The primary benefit of the supergrid is that it aggregates wind power across geographically dispersed areas, and, by doing so, it smoothes the output of those wind farms,” says Chris Veal, the Airtricity director promoting the supergrid. “If the wind isn’t blowing in the Irish seas, it’s likely to be blowing in the North Sea or the Baltic. The wind is always blowing somewhere.”

By solving two problems at once – interlinking grids and providing hookups for more offshore wind farms – Veal thinks Airtricity has found a solution that’s economically feasible. “It’s something the market can do,” he says.

Airtricity proposes to start by building a massive 20 billion euro ($23.8 billion) project in the North Sea. Last November, Swiss-based ABB completed a study mapping out the power links for a group of wind farms that Airtricity would like to build in the southern half of the North Sea. (Airtricity is vague on the exact location, since it is still staking claim to the seabed, which lies in the U.K., German, and Dutch waters.) The wind farms would produce 10,000 megawatts of electricity – 50 times more than today’s biggest offshore farms.

A 5,000 megawatt DC power line would carry power west to the U.K., and a second 5,000 megawatt line would run east to continental Europe, perhaps to the Netherlands. When the wind is too calm to produce power – about 60 percent of the time at Airtricity’s North Sea sites – the lines would go into interconnect mode, carrying 5,000 megawatts of electricity in either direction. This would, for example, more than double the U.K.’s energy-trading capacity, making that country’s grid more stable and giving its consumers access to a wider range of power producers.

This flexible DC network would be made possible by digitally controlled, high-voltage DC power converters, a technology that has been entering the market over the past five years. The key, says ABB project manager Lars Stendius, is the newer technology’s ability to reverse a line’s current without changing the “polarity” of its voltage.

Veal says the ambitious project would take five years to build and construction could start as soon as 2010. At the moment, Airtricity is looking for partners to help finance it, including transmission players who could profit from the proposed energy trading.

Hydropower could play a key role, too. Gregor Czisch, an energy systems modeling expert at the University of Kassel in Germany, says the benefits of a European supergrid linking Mediterranean and North Sea wind farms with Norway’s immense hydropower reservoirs would be “considerable.” Those reservoirs could be tapped during periods of low wind, providing a renewable backup to the wind power.

But, to Czisch, solidifying the European grid is just a first step. His optimization studies show that the benefits of the supergrid multiply if one extends high-voltage DC lines beyond Europe to North Africa and the Middle East. By doing so, he says, one could ensure that there was always enough output from renewable sources, such as wind plants and solar panels, to power an area spanning 50 countries and 1.1 billion people.

In Czisch’s visionary scenarios, wind power alone provides 70 percent of the region’s total power, thanks largely to excellent wind resources in Egypt and Morocco that flow more powerfully and more consistently than Europe’s. And it’s affordable: including the power lines, Czisch estimates that under his scheme electricity consumed in Europe (including the African wind power) would cost about 4.6 eurocents per kilowatt-hour – about the same as the European average. “It’s no more expensive than our existing power supply, with no fossil fuels and no nuclear,” he says.

The challenge is to get the supergrid onto the policy agenda. Because it’s a big-energy concept, Czisch says, it runs counter to the thinking of many renewable energy advocates, who he believes prefer to see renewable energy as local energy sources, such as solar panels on rooftops. “You would have to build huge high-voltage DC lines, huge wind-power plants in Morocco, and so on. This is something that could easily be done by the big utilities – but the utilities are the enemy of the renewables people,” he says.

Airtricity’s Veal is hoping to get some help from the European Commission, which just released a proposal for an integrated European energy policy. “We’re not going to solve all of the EC’s problems,” Veal says, “but we can be a major contributor.”

Peter Fairley is a TR contributing writer based in Paris.