A group that includes a unit of Siemens has acquired a planned project to build a nearly 350-mile-long, 2,100 megawatt (MW), high voltage direct current (HVDC) electric transmission line to link wind energy resources in Iowa with demand load centers in the eastern U.S.

The 525 kilovolt (kv) project would cost around $2.5 billion and could enter service by 2024. Local, state and federal approvals would be required before construction can begin.

If approved, the SOO Green project would follow a route from Mason City, Iowa, to grid interconnect points near Chicago. The route in part would follow existing railroad lines, primarily along the Canadian Pacific railroad, and would be buried.

Primary investors include Copenhagen Infrastructure Partners, Jingoli Power, and Siemens Financial Services. Direct Connect Development Co. is leading the project team.

HVDC works by taking electric power from one point in a three-phase AC network, converting it to DC in a converter station, transmitting the energy to a receiving point by line or cable and then converting the current back to AC in another converter station and injecting it into the receiving AC network.

About 130,000 MW of HVDC transmission capacity is installed in more than 140 projects worldwide. One of the first commercial HVDC schemes was commissioned in 1954 and linked the Swedish mainland with an island in the Baltic sea. The power rating was 20 MW and the transmission voltage was 100 kV.

The technology improved in 1970 when thyristor valves replaced mercury arc valves. This reduced the size and complexity of HVDC converter stations. More recently, microcomputer control equipment has led to additional improvements.

In the proposed Iowa project, the cables would be buried in a 2.5 ft wide x 5 ft deep trench, mostly along the railroad right of way. Burying the lines and co-locating the project with the railroad is expected to streamline permitting and avoid at least some landowner opposition.

SOO Green would be a merchant transmission line, meaning that utilities or other wholesale power customers that buy transmission service on the line would pay for it.

Wind leader

The American Wind Energy Association (AWEA) said that in 2017 Iowa generated 37% of its electricity from wind power. The state ranked first in the nation for wind energy as a share of total electricity generation. Iowa ranks second in the nation for installed capacity with 8,422 MW from more than 110 projects. Another 1,667 MW of capacity is under construction. AWEA said that 1,600 MW is in advanced stages of development.

The SOO Green project initially was owned by an unnamed group of private investors and Canadian Pacific, the Des Moines Register newspaper reported. In addition to becoming a new investor in the project, Siemens was tapped to manage design, engineering and manufacturing of HVDC converter stations.