An Argument for Superconducting HVDC Interconnects – A Space for My Projects, Thoughts, and More…

Recent years have seen a rapid increase in the availability of REBCO superconducting tapes, commonly referred to as high temperature superconductors (HTS) for their ability to function up to liquid nitrogen temperatures (77K). Current capacity under these conditions is limited however, and much more important particularly in fusion applications is the higher magnetic field tolerance – up to 25T at 20K.

For long distance power transmission, 77K operating conditions may be desirable for practicality depending on the cost of the tape itself compared to the cryogenic cooling system.

Below is a plot of resistive efficiency and power loss for a 1GW, 1000km HVDC line, using an aluminum conductor. The required conductor cross-sectional area depends greatly on voltage (P=I^2 R), with 86% efficiency requiring only 2cm^2 at 1000kV, but 200cm^2 at 100kV.

This provides a strong incentive for increasing voltages up to UHVDC (>800kV), with conductor costs of only around $1-2/GWm at 1000MV, compared to $100-200/GWm at 100kV. A heavy cost is incurred however in the substations and line insulation.

It is at these lower voltages that the use of superconductors begins to look highly attractive from a purely cost perspective. As of 2025 HTS tapes have dropped below $1/kAm, corresponding to power-per-unit-length price of $10/GWm at 100kV, under 1/8th that of a 100cm^2 aluminum conductor operating at only 73% efficiency.

Update – Looks like actual HTS projects have been running since the early 2000’s. There is a US company building LN2 evaporation cooled HTS overhead lines. Power level appears to be 400MW at 69kV (5.8kA) though the number of conductors and AC/DC are not specified.

https://en.wikipedia.org/wiki/Holbrook_Superconductor_Project

https://en.wikipedia.org/wiki/Electric_power_transmission#Superconducting_cables

https://news.mit.edu/2024/veir-transforms-power-grid-with-superconducting-transmission-lines-0626

https://veir.com/

The Importance of Efficiency and Heat

The above comparisons have given two generous allowances to conventional conductors: no consideration for the wasted value of electricity, and no concern for heat buildup in the lines.

If we assume an electricity value at the end destination of $0.20/kWh ($200/MWh), a one GW line would deliver $0.2M of electricity per hour, or $1.75B per annum. A penalty of $1.75M per MW lost per annum, or $17.5M per % is thus incurred.

Heat buildup is a further concern, particular for buried lines. A 100cm^2 conductor at 500kV must dissipate 10W per meter, with that value increasing to 250W at 100kV. Mitigation means either cooling solutions – pressurized oil or gas, or reduced current density, both of which impose costs. A superconducting line experiences none of this, with the only heat flow being that needed to compensate for leakage across the thermal insulation.

Volume Reduction

An additional benefit is the reduction in conductor area. 33 layers of 12mm tape at 77K have a combined current capacity of 10kA, whilst taking up only around 12×3.3mm (3.96cm^2). Consideration must be made of course for cryogen and insulation space, however total area would likely still fall well under that of an aluminium conductor – 100cm2 at 73% efficiency. Such reductions reduce insulation and sheath costs, as well as simplifying the installation process – a 100cm^2 conductor has a weight of over 27,000 tonnes per thousand km even before insulation and sheathing.

Above: Aluminium conductor efficiency and heat generation with respect to voltage for a 100km 1GW HVDC transmission line. Note: title voltage and current range is incorrect.

A Note on the Cost Potential of HTS

(Diagram taken from M. Bonura, L. Bottura, S. Rossi, et al., “Soldered joints—an essential component of demountable high temperature superconducting fusion magnets,” Supercond. Sci. Technol., vol. 29, no. 7, p. 075005, 2016. https://doi.org/10.1088/0953-2048/29/7/075005)

An interesting side point is on the cost potential of HTS. Notably the superconducting layer itself is very thin, only around 1-3um typically, with the majority of the thickness made up by the 50um hastalloy substrate and 20um copper stabilizers. Costs are dominated by the silver layers despite their only ~2um thickness, until the REBCO cost approaches $10,000USD/kg. Even at this price point however, the total material cost only roughly doubles from $0.81/m to $1.72/m.

The conclusion to draw here is that depending on the price of deposited REBCO, HTS tape has the potential to reach prices under $1USD/m, particularly if the silver layers can be eliminated or substituted as is being done in solar panel manufacture.

A Cost per Area Analogy to Solar Panels

In 2025, 500W solar panels can be purchased in New Zealand at an astonishingly low retail price of $140NZD – $280NZD/kW. As a side note, with our nationwide capacity factor of 17%, this works out to a cost-per-kW-continuous of $1647NZD.

Let’s assume a solar panel area of 2.5sqm/500W, which would correspond to an efficiency slightly over 20% to take into account gaps between cells. The area cost is thus $56/sqm, or 0.56 cents per cm2. A 12mm wide by 1m long strip of panel would then cost $0.672. These panels comprise about 3mm of glass, the silicon cells and current collectors, an aluminium frame, and the power connector. Compare that for scale to the ~0.1mm thickness of a HTS tape.