Skagerrak is the name of a 1,700 MW high-voltage direct current (HVDC) transmission facility between Tjele (Denmark) and Kristiansand (Norway). It is owned and operated by Statnett in Norway, and Energinet in Denmark. The lines connect the hydroelectric-based Norwegian grid and the wind and thermal power-based Danish grid. In operation it enables more renewable energy in the energy mix, and more efficient use of electricity. Technical features The Skagerrak 1–3 scheme consists of a overhead line and a underwater cable. It has a capacity of 1,050 megawatts (MW). Both land parts in Denmark and in Norway uses overhead lines from the cable landing point to the converter stations. The overhead lines in Denmark are set to be renovated in 2016 for increased lifespan. The towers were originally constructed for four poles, but were rebuilt for three conductors (three poles) when Skagerrak 3 was established. Near Aggersund HVDC Skagerrak crossed Aggersund strait overhead on towers with a span, but were later converted to underground cables. The pylons of this span were the tallest electricity pylons of an HVDC line in Europe. For such a long submarine cable, an AC transmission scheme would not be feasible since too much of the cable's capacity would be consumed by the capacitance of the cable itself, and the power systems in Norway and Jutland are not synchronous. The transmission has a loss rate of 4%. The waste heat of the transformers is enough to supply district heating economically for 1,000 homes in nearby towns, but taxes prevent that project. The adjacent Apple Datacenter (supplied in part by the Skagerrak cables via Tjele) was expected to work around the tax issue when supplying district heat to Viborg. Skagerrak 1 and 2 Skagerrak went in service in 1977 as a bipolar HVDC scheme. This facility was built with thyristor valves. When installed this underwater cable was the world's longest and deepest underwater HVDC power cable. The cable, manufactured by Alcatel, is laid in a maximum water depth of . Both cables have a capacity of 250 MW at 250 kV. Skagerrak 3 In 1993 the scheme was extended by HVDC Skagerrak 3. Skagerrak 3 is a monopolar line for a voltage of 350 kV with a capacity of 440 MW at 350 kV. In installing Skagerrak 3, the old poles Skagerrak 1 and Skagerrak 2 were converted to monopolar HVDC schemes, which run with opposite polarity to