Transmission fortnight: burying power lines next to rail & roads to make a national transmission grid

Happy Monday! Welcome back to Transmission Fortnight here at Volts. Today’s a fun one.

In my previous post, I described the many difficulties facing new high-voltage, long-distance transmission projects, from planning to financing to permitting and siting. It’s a bureaucratic slog.

Today we’re going to look at a clever idea for bypassing many of those problems, namely, stitching together a national power grid by burying power lines along existing rail and road infrastructure, where rights-of-way are already established, thus eliminating the endless haggling with local governments and landowners.

The idea has been gaining steam in the policy community for the last few years. FERC issued a report in June on challenges to transmission; siting along existing infrastructure was cited as a promising solution. In his Build Back Better plan, Biden promised to “take advantage of existing rights-of-way — along roads and railways — and cut red-tape to promote faster and easier [transmission] permitting.” This op-ed in The Hill sums up the benefits quite nicely, both of a national grid and of building it without siting battles.

The vision is taking hold. And at least one small piece of that vision has gone beyond speculation into an actual permitting process.

The SOO Green line will carry Iowa wind power to Chicago

A company called Direct Connect is currently in the development and permitting phase of a privately financed, $2.5 billion project called the SOO Green HVDC Link, a proposed 349-mile, 2.1-gigawatt (!), 525-kilovolt transmission line to run underground along existing railroad from Mason City, Iowa, to the Chicago, Illinois, area. It aims to go into operation in 2024.

Going underground will allow the line to minimize environmental and visual impact. It will be much more resilient than an overhead line against weather, temperature shifts, sabotage, or squirrels.

Two side-by-side cables will run through tubes of Cross-Linked Polyethylene (XLPE) and will be self-contained, lightweight, and easy to handle. They won’t get hot, interfere with signaling equipment (unlike AC lines), or affect rail operations. There are fiber-optic sensors along the lines to monitor sound and heat for any problems.

(Nemo Link, the world’s first 400 kilovolt line using XLPE, runs undersea between the UK and Belgium; it began operation in January 2019.)

Running alongside the railroad means SOO Green will have no need to claim land via eminent domain. Almost all of that railroad is owned by Canadian Pacific (one of seven large “class one” railroads in the US), so there are a tractable number of parties to deal with.

A deal like this offers railroads a new passive revenue stream; royalty fees well exceed what they get from similarly buried fiber-optic lines, of which there are more than 100,000 miles along US railroads. And it’s also a chance for railroads to be part of a positive sustainability story.

The project is privately funded, so there will be no need for any complicated cost-allocation formulas. The financiers (including Siemens, which very rarely puts direct capital in transmission projects) will make their money back from those who use the line — the suppliers that put power on it, the shippers that sell power across it, and the buyers that consume the power — through competitive bidding for capacity. SOO Green is holding an open solicitation right now to allocate its 2,100 megawatts among them.

The aim is to create a more robust energy market by, for the first time, connecting the MISO and PJM territories. (MISO and PJM are regional transmission organizations; see previous post for details.) Wind power projects are backed up in MISO, waiting to connect, stymied by grid congestion. Meanwhile, nextdoor neighbor PJM is the largest liquid energy market in the world.

The idea is that SOO Green will unlock renewable energy development in MISO; Direct Connect projects four to six new gigawatts. That energy will be transported to population centers in PJM, easing grid congestion, reducing the carbon intensity of the East Coast energy mix, and lowering power prices.

The connection will also allow MISO and PJM to share reserves for the first time, which could reduce the need for reserve capacity, increase reliability, and save consumers money.

Because the MISO side will be drawing from such a geographically broad region, it is likely to be in use almost continuously. “When the wind isn't blowing in North Dakota, it likely is in Minnesota,” Trey Ward, the CEO of Direct Connect, told me. “We anticipate upwards of 90 percent line utilization.”

“It's as if we teleported a 2,100-megawatt wind turbine with a 90 percent capacity factor from Iowa into suburban Chicago,” he says. In fact, the converter station in PJM has applied to be treated as a capacity source in that market. (That will require some updating of regulations, just as power market regulations had to be updated to accommodate batteries.)

The converter stations at each end of the line are worth looking at more closely. They will use the latest generation of Voltage Source Converters (VSCs) to exchange power between the HVDC line and the regional high-voltage alternating current (HVAC) systems already in place.

VSC technology has been around since the late 1990s, but it has only recently gotten efficient, compact, and cheap enough to compete against the thyristors (solid-state valves) in common use today on HVDC lines.

VSCs boast several important advantages. Thyristors need strong AC systems on both sides of the line, they require power filtering, and they have limited control over reactive power. (Do not ask me, or anyone else, what “reactive power” is. That way lies madness.)

VSCs, on the other hand, are “self-commutated converters,” which means they can generate AC voltages (using IGBT capacitors) without relying on an AC system. They can control power independently, even with a weak AC system or no AC current at all; they can “black start” a grid from a blackout automatically, without any workers out throwing switches.

VSCs allow precise and instantaneous, bi-directional control of both active and reactive power. They can provide services to the grid other than just energy — things like voltage and frequency regulation or “synthetic inertia” to support