What are carbon nanotubes?


The discovery of carbon nanotubes (CNTs) has the potential to change every industry. Navigant Research explores these tiny marvels in more depth.

This article was originally published in Smart Energy International 4-2018

A CNT is a small carbon cylindrical structure, and eventually will be implemented into high-performance products in many industries all over the world. Among the most significant scientific discoveries of our time, a CNT is extremely strong for its size and weight, and highly conductive, making it an ideal material for electrical transmission and eventually distribution networks.

CNTs can take many shapes, and each variance has its own set of advantages and challenges in manufacturing and deployments.

Navigant Research assessed the current status of the market for CNTs for grid applications in a recent report, concluding that manufacturing and reductions in cost are pivotal to eventual deployment. However, CNTs have already begun providing transmission and distribution (T&D) cable manufacturers the opportunity to partner with CNT manufacturers to build a cable that is superior to anything that currently exists. In May 2017, Prysmian Group, one of the world’s leading industrial cable manufacturers, partnered with Nanocomp Technologies to “fit nanotechnologies to cable systems for power grids.” Partnerships like this will push up the timeline for the eventual widescale integration of CNTs into T&D networks.

Carbon nanotubes on the grid

The strength, weight, elasticity, and conductivity of CNTs make them ideal for deployment on the electrical grid. With a tensile strength of up to 100 times greater and a density of just one-fifth that of steel, CNTs display a strength-to-weight ratio unmatched by any material currently used for T&D networks. Additionally, CNTs require five times more force to bend than steel, are five times more electrically conductive, are 15 times more thermally conductive, and can carry 1,000 times more current capacity than copper.

These characteristics position CNTs with the ability to deliver high amounts of power over long distances using very small and lightweight power cables. However, there are significant drawbacks and roadblocks that must be overcome before this goal can be attained.

The first is the size of a CNT. Typically, the diameter of a CNT is measured in nanometers, with one nanometer being 10,000 times smaller than a human hair. With its microscopic size, manufacturing a CNT into a cable is not possible at this time. However, CNT vendors and labs have begun to integrate CNTs into carbon fibre materials, including bicycles, hockey sticks, tennis racquets, car parts, and other items. CNT fibres are often constructed into a variety of materials including yarn, fibres, pulp, paper, fabric, laminate and other products as well. These are the types of materials that cable manufacturers and energy industry engineers are exploring for applications to the grid.

Due to the extremely small size and complex construction of a CNT, manufacturing prices are currently astronomical. Reported manufacturing costs range from $50 to over $1,000 per gram of pure CNT material. In addition to the costs, there are limitations on current CNT manufacturing capabilities, and the efficient construction of tubes longer than several centimetres still sits as a major roadblock to deployment in many industries – particularly for T&D applications. However, with the development of new CNT constructions such as tape, coatings, and yarn, and hybrid constructions with other materials, the eventual integration of CNTs on the grid is beginning to look more and more like a reality.

Application: Insulative coating

When and if CNTs are eventually deployed on the grid, expect a variety of material combinations, CNT constructions, and integration with existing grid equipment. For example, one specific application for CNTs on the T&D grid is the use of a CNT coating for cable insulation. In their 2016 study, High-Ampacity Overhead Power Lines with Carbon Nanostructure-Epoxy Composites, Kumar, Kumar, Pal and Shah discuss a CNT coating for electric transmission lines. By layering a CNT coating around an aluminium conductor transmission line, the operating temperature can be reduced and the overall transmission efficiency can be drastically increased. This application takes advantage of the insulative properties of specific CNT constructions, rather than the conductive properties of others. This will allow cable manufacturers to drastically reduce cable weight, saving on network infrastructure costs and insulation material manufacturing. The study found a reduction in aluminium of 25% and an increase in possible span length of 30% by applying the CNT coating technology to an aluminium conductor-composite core transmission line.

What about the distribution network?

The distribution network will likely lag behind the transmission network in the eventual applications of CNT technology due to foundational differences between the networks. Transmission lines are heavy, carry high capacities and voltages, and span long distances. The integration of CNT technology stands to significantly enhance and even transform every aspect of a transmission line. Distribution lines, on the other hand, are shorter, lighter, smaller, and carry less power. While the advantages of a CNT-enhanced cable would definitely apply to the distribution network, the technology in its current and near-future state will likely prove too expensive to justify the scale of the benefits.

Looking ahead

As the T&D networks evolve, so to will the technologies used to create them. CNTs stand to deliver benefits unmatched by any other material for power transmission, and the onus now rests on market participants across the value chain to continue to find ways to integrate the technology. Yet, with continued scientific progress, strong partnerships across all industry participants, and a drive by utilities to revolutionise their electric grids, CNTs might just have a chance to change the industry. SEI

You can find more information in the report: Improving Transmission Efficiency with Carbon Nanotube Technology.