Tres Amigas LLC, the partnership planning a superconducting, direct-current transmission hub to connect the Texas, Eastern and Western U.S. grids, has raised $12 million from Japanese financial giant Mitsui & Co. The investment adds to $3 million raised in November to complete a planned $15 million round.

That's a good first step, but still far away from the $1.5 billion in anticipated costs for Tres Amigas' ambitious plans to create a first-of-a-kind power exchange and balancing hub for the U.S. power grid system. We're seeing similar interesting grid-balancing projects emerging, such as Japan's Digital Grid Consortium. Here's what Tres Amigas is planning to do with the money it has raised.

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The Tres Amigas partnership -- a sprawling collection of grid and infrastructure giants like U.S.-based CH2M Hill and France’s Alstom and startups like battery maker Xtreme Power and microgrid software vendor Viridity Energy -- wants to build a massive triangle of battery-backed transmission lines to connect the three main U.S. grid systems near the town of Clovis, New Mexico, where they happen to be pretty close to one another.

The United States has three separate grid systems -- Eastern, Western, and Texas -- that don't interconnect. But there are a lot of West Texas wind farms that need more customers for their power, as shown by the negative prices Texas wind farms sometimes pay to supply excess wind power to the Texas grid. Soon enough, there could be a lot of southwest solar power coming online that could really use spare transmission lines to get the power to the cities that need the juice.

Tres Amigas plans to build superconducting high-voltage, direct current lines to connect the three grids, then broker power exchanges between the three grids, kind of like the way a tollkeeper on the Triborough Bridge brokers the flow of vehicles between Queens, Manhattan and the Bronx. Revenues from the Tres Amigas operation, projected to be as high as $4 billion a year by the project’s backers, are meant to pay back the $600 million to $1 billion in estimated construction costs.

It’s the kind of audacious plan that will require a lot of regulatory changes to make work. Last year, the Federal Energy Regulatory Commission (FERC) ruled that the project could go forward, but held off on giving the project expedited approval until ERCOT, the Texas grid operator that’s partly free of federal oversight since it operates within one state’s boundaries, subjects itself to some sort of federal authority over how it interconnects with other states.

In September 2010, FERC denied a protest (PDF) to that ERCOT ruling filed by Occidental Chemical Corp., Occidental Power Marketing and a Texas industrial energy consumers trade group. In August, Tres Amigas said (PDF) that its plan was to “focus on the linkage between the Eastern Interconnection and the Western Electricity Coordinating Council (WECC),” or just the Eastern and Western grids, until the FERC-ERCOT issue was resolved.

Tres Amigas also announced in August that was negotiating with a potential first anchor customer for its brokered power and hoped to name that customer by year’s end. It also said it was negotiating interconnection agreements with Amarillo, TX-based Southwestern Public Service (SPS) Company and Albuquerque-based Public Service Company of New Mexico.

If built, the project will be one of the largest in the world delivering large-scale power via superconducting direct current (DC) lines, as opposed to alternating current (AC), an innovation that should cut down significantly on the power lost in transmission. American Superconductor is supplying the superconducting wire, and Alstom will use it to build the DC transmission lines.

Tres Amigas’ SEC filing listed no profits (not surprising), and noted that $1.1 million of the $15 million being sought is expected to go to executive officers, directors and “promoters” of the project. No word yet on progress on raising the investment needed to get the thing off the ground.

A billion dollars sounds like a lot, but it pales in relation to figures like the $200 billion the Western Interconnect expects to need to spend to upgrade its system to manage all the renewable power and new customers it serves. Big transmission needs lots of cash. No word from Tres Amigas on how project financing is going, but the partnership is aiming to start construction in 2012 and have the hub up and running by 2014.

Tags: alstom, ch2m hill, smart grid, solar power, southwest, superconductor, texas, transmission, tres amigas, viridity energy, wind power, xtreme power