Transmission & distribution |
Why we need to carbonise the grid
The grid is being required to carry loads it was never designed to handle. One potential solution is deployment of radically improved conductors based on carbon nanotubes. But to achieve this, carbon nanotube prices need to come down and the manufacturing precision needs to be driven up
Alvin Orbaek White CEO, TrimTabs Ltd
The world is reaching an energy crisis. Higher energy consumption, particularly electricity, is a direct marker of a nation’s development level and as the world population grows, more people will require electricity to meet their increased living standards. With a projected rise in global population from 6.5 billion in 2004 to over 9 billion in 2050, there will be a need for a 100- 400% increase from existing energy production. Producing enough energy is less of a problem than expected; distributing it becomes a more critical issue. Copper and aluminium cables are reaching peak efficiency since power is lost during transmission due to heating effects from intrinsic electrical resistance within the cables, over 10% in the case of the UK, for example.
Grid at a crossroads Electrical conductivity in materials is a phenomenon well-understood by the energy sector. Metals, semiconductors, and electrolytes—each play a pivotal role in the conduction of electricity. Metals, with their loosely bound electrons, stand as the backbone of our current electrical infrastructure. Yet, as demand skyrockets and the push towards renewable energy strengthens, we find our grid at a crossroads. The conduits that have served us for decades are being asked to carry a load they were never designed to handle. At the heart of the grid’s issues lies its ageing infrastructure. Conventional aluminium conductor steel reinforced (ACSR) cables, the grid’s mainstay, are reaching their limits. These lines, heavy and burdened by their steel support, limit the volume of electricity that can be transmitted. Innovations like composite materials for conductor cores promise a remedy by allowing more aluminium, thus more capacity, without requiring new permits. But using that material will cause more of the same problems we suffer now.
Electricity transmission is a surface phenomenon, and this can be leveraged by increasing the cable surface area to improve electrical load. However, this approach makes cables thicker and heavier. It initially increases the current rating, but under continued electrical load, they heat up due to intrinsic electrical resistance and then undergo thermal expansion. The cables sag from expansion, confounded by their density and weight. The metal stretches thinner, constricting the surface
Figure 1. At a magnification of 3000x, carbon nanotubes appear as long strands
area around the circumference, leading to increased resistance. Higher electrical loads compensate for the added resistance, thus causing further resistive heating. The problem can continue until there is a brownout or blackout event. All the while, electrical power is emitted as wasted thermal radiation to the atmosphere. Cables can’t be placed underground unless actively cooled at an additional energy cost to install and maintain.
Vastly improved cable needed The key technical component of a highly efficient power grid is a vastly improved power cable (a ‘quantum’ conductor) with which to rewire the electrical transmission grid, to enable continental and even worldwide electrical energy transport. Carbon nanotubes (an allotrope of carbon) are hollow nanoscale tubes consisting of carbon atoms. A carbon wire employing carbon nanotubes offers the potential keystone technology to enable these low-loss transmission cables. One particular “armchair” structural type of SWCNT (Single Wall Carbon Nano Tube), for example, has 1/6th the weight of copper and can conduct electricity at room temperature with near-zero power loss1,2 over great distances due to ballistic electron transport along the nanotube axis.3
Carbon
cables of this nature are superior to copper wire4
when normalised according to the mass density. However, the fundamental bottleneck in this approach is the length of each SWCNT. Longer SWCNTs reduce the number of tube–
22 | March 2024|
www.modernpowersystems.com
tube junctions, lowering junction resistance along the cable.
The aspect ratio (length-to-diameter) is the most important factor currently controlling strength and electrical conductivity. Large aspect ratios, of the order of “30k” or greater, are required. This correlates to SWCNTs with small diameters (1-2 nm) and ultralong length scales (1-50 cm); the future is transmission cables made from ultralong single-walled carbon nanotubes.
When encountered in the real world, you can tell there is something unique about nanotubes; they are the world’s blackest material and looking inside a nanotube-filled container seems akin to experiencing the event horizon of a black hole. No light escapes because they can absorb up to 99.995% of all incoming light, the blackness seems infinite, and pictures don’t do it justice.
But when we zoom in, some clarity appears; at a magnification of 3000x, the nanotubes appear as long strands (Figure 1), often wavy, but they can also be made to align, which is key to making long-range power transmission as effective as possible.
On an individual scale, seen at a magnification of 630 000x (Figure 2) using a transmission electron microscope, one can see the concentric walls that make up the multi-walled tube. We foresee these intrinsic directional materials being fashioned into global electron highways. At the molecular level, nanotubes are wire shaped and they are also intrinsically large-
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