Gotland, off Sweden's east coast in the Baltic Sea, has an isolated power grid connected to the mainland by a high voltage DC cable, which can only transmit power in one direction -- from the mainland to Gotland. The over production is not a serious problem yet -- stopping a few turbines for a few hours hardly affects economic returns, say the operators. But Gotland is likely to double its wind power capacity in the next few years, hastening the search for a solution.
Local utility GEAB's priority is a grid reinforcement allowing more wind generated electricity, estimated to cost SEK 150 million. Following the summer's wind surplus, the utility has doubled the grid connection fee for wind turbines from SEK 600/kW to SEK 1200/kW as a way to help finance the reinforcement. GEAB reports the fee increase was in response to a complaint from a consumer demanding that reinforcements for wind power be financed solely by wind power producers, not consumers. The utility's Christer Liljengren says he would have preferred a special grid levy on the kWh price of wind output, but current regulations do not allow that.
The Gotland wind power association GVP has reacted strongly to the move. While such fees do not exist on the mainland, the SEK 600/kW grid connection fee had been based on a mutual agreement between the utility and the wind plant operators. Raising the fee without prior consultation with GVP is seen as a move to stop further development without any backing in laws or regulations. The association claims the SEK 1200 will effectively stop further wind development in its tracks.
GEAB is discussing the matter with central authorities, looking for state financing to offset the reinforcement costs, which the small utility says should not be borne by itself alone. Since 1990, GEAB has reinforced the grid twice after wind power development at Gotland's Näsudden site was much faster than expected. And now the country's first offshore wind farm is being built off the Näsudden coast.
The level of grid reinforcement needed to handle wind power development over coming decades is hard to estimate. Today's 32 MW capacity at Näsudden could double within a few years -- and there are plans for groups of several 1.5 MW turbines in other areas of Gotland as well as a series of offshore wind farms of 30-50 MW around the island's coastline.
GVP has suggested retrofitting the DC mainland link to a two-way connection by using the stand-by cable, a task estimated to cost SEK 5 million. GEAB is considering this suggestion, but Liljengren notes that the risk of power outages would increase without another standby cable.
Another proposal calls for a new DC link from the wind power concentration at Näsudden to a substation close to Visby, where the mainland cable connects to the local grid. This way the power from Näsudden could be used in Visby, Gotland's largest city, and at the cement factory in northern Gotland; any surplus power could be transmitted to the mainland. The local grid in southern Gotland could thus take more power from other areas.
GEAB is also considering a test of new technology developed by international electrical engineering company Asea Brown Boveri (ABB), which allows large, offshore wind farms to connect to a mainland grid with a minimum of loss. Due to its R&D nature, the project could be financed by government agency Nutek and other central institutions. If all parties decide to go through with it, the link could be in operation within two to three years.