This is the second article in a two-part series about investing in grid technologies. Read the first part here.
In our previous article we explored the challenges that grids around the world face and what needs to be addressed to support the energy transition. Here we ask: what are some of the technologies that are emerging to tackle these two primary challenges of expanding grid capacity and accommodating its increasing complexity?
I explore some of the hardware-based solutions proposed and in development. It is worth noting that many of these solutions are technically-proven and already (or close-to being) commercially available. Some might even argue that it is not a technology problem at all but a financial and structural one—that the main bottleneck is permitting timelines for grid expansion and connections.
We must also acknowledge that there is much innovation happening in grid technologies from a software perspective to (i) enable a smart grid, (ii) allow for more efficient planning and electricity flows and (iii) manage distributed energy resources (DERs) at the grid edge via aggregators and virtual power plants (VPPs). Given that our focus at ZCC is on hardware solutions for the climate crisis (you can read more about our thesis here), I will limit my focus to physical technologies. Let’s take a look!
Technologies to increase capacity
There are a number of technologies that are commercially available, where wider deployment would increase the power capacity of the grid beyond simply building new lines. The value proposition here is that although the upfront cost may be higher than business-as-usual, the increased capacity would improve reliability, reduce congestion and defer T&D upgrades, lowering costs overall. These are covered in more detail elsewhere, including in the DOE's recent Grid Liftoff Report, but we review them briefly below.
Dynamic line rating (DLR): adding sensors and control algorithms to increase the capacity of existing transmission
Transmission lines can only safely handle a certain level of electric current based on thermal and physical constraints before equipment risks damage. The maximum current carrying capacity of any line depends on its thermal limit. This limit depends on both environmental factors such as weather conditions (wind vs sun) and direct conductor properties (like sag, tension and clearance).
Line ratings are assigned to power lines to prevent them exceeding this thermal limit. These ratings are established through modelling and approximations and are usually static, although they are sometimes seasonal to account for different average temperatures.
Dynamic line ratings (DLR) are technologies and methodologies that determine conductor thermal ratings in a dynamic fashion using granular or real-time data based on the environmental and physical factors mentioned above. Direct measurements are usually more accurate but require sensors which are more costly and time consuming to install. Many startups are working on sensor technologies and DLR algorithms, including LineVision (non-contact sensors for DLR), Ampacimon, Atecnum and Prisma Photonics. DLR is currently installed in at least 12 countries worldwide, and can enable up to 40% higher current carrying capacity comparing to static ratings.
✅ Advantages
Capacity increases: static ratings are typically extremely conservative, because reliability and resilience are more important that efficiency.
Sometimes capacity from DLR is more than double that of static rating, usually on cloudy, windy days, when solar irradiance is low and cooling from wind is high
Congestion benefits: more power can travel along a given line = less curtailment.
Cost savings: increasing capacity of existing T&D networks reduces need for new lines
Asset health monitoring as an additional benefit of sensors
❌ Barriers
Insufficient incentives for transmissions owners with current remuneration models
Required operational knowledge–requires new hardware but also new control room software
May not be as good for lifetime to always run line close to its limit–easier to maintain safety with simpler static ratings
Advanced power flow control (APFC) for power quality control (and congestion relief)
The power flow on transmission grids is dictated by the laws of physics—electricity takes the path of least resistance, so power flow can be managed by changing the resistance. Advanced Power Flow Control (APFC) devices are modular power electronics-based devices that can control the resistance/reactance on the transmission grid to temporarily re-route power flows. This results in better use of existing grid infrastructure by minimising congestion, increasing overall capacity, and therefore minimising the amount of additional capacity that needs to be built. These power electronics provides additional services like voltage stability. SmartWires is a key innovator in this space.
✅ Advantages
Alleviate congestion by dynamically re-routing power flows
Optimise asset utilisation through flow control instead of just adding new lines
Enhance grid resilience and stability through rapid response
❌ Barriers
High upfront costs of power flow control equipment
Reconductoring with higher capacity cables: advanced conductors and superconductors
Traditional overhead conductors are made of aluminium and steel, with aluminium as the main conducting material, and a steel core or steel support strands for strength (these are known as Aluminium Conductor Steel Reinforced (ACSR) and Aluminium Conductor Steel Supported (ACSS) conductors).
Advanced core conductors use innovative materials like aluminium alloy, carbon fibre, and composite cores to replace traditional steel cores, these are lighter weight, with reduced sag and therefore have higher current carrying capacity under high loads. About 200 reconductoring projects using advanced conductors have already been installed in the U.S.. Some examples are Aluminium Conductor Composite Core (ACCC), Aluminium Conductor Composite Reinforced (ACCR), and UltraCoreTM.
By replacing existing cables with higher capacity advanced conductors, grid operators can increase capacity and reduce congestion whilst taking advantage of existing rights of way, and deferring the buildout of new lines.
Smart wire technologies go even further, integrating fibre optic sensors into these advanced conductors to enable real-time monitoring of key parameters like temperature, sag, strain, and local weather. This facilitates dynamic line rating and asset health monitoring as well as increasing current carrying capacity.
High temperature superconductors (HTS) like yttrium barium copper oxide (YBCO) allow close-to loss-free power flow when cooled to cryogenic temperatures using liquid nitrogen–these require temperatures of around 77 K. HTS cables can carry 5-10 times more power than conventional lines. Companies like American Superconductor, Nexans, and VEIR are developing HTS solutions.
✅ Advantages
Increased capacity–can carry 2x to 4x more current than conventional conductors
Reconductoring reduces cost overall by reducing amount of new transmission required
Reduced sag and improved thermal performance under high load conditions
Higher strength-to-weight ratio allowing longer spans between towers
❌ Barriers
Higher upfront costs: 2-4x higher CAPEX hard to justify even if lower OPEX
Licensing of new designs and potential grid integration challenges.
High-voltage direct current (HVDC) grids
Direct current grids are less widely used than AC grids to date. The main reason for this is that AC systems can readily step the voltage up or down using transformers, whereas DC systems require more expensive converters.
However, high-voltage direct current (HVDC) has some key advantages that make it a useful tool for decarbonisation, particularly for long distance high-voltage transmission, integration of offshore wind, and interconnection of asynchronous grids. So the ask here isn’t so much for investment to develop the technology, but rather a system-level investment into building higher-efficiency (and certainly least-cost overall) HVDC networks, as has been done in China. China has rapidly deployed a HVDC supergrid to connect remote (currently coal-fired) power stations to densely-populated load centres like Shanghai.
There are number of HVDC links in Europe: mostly the sea-crossing interconnectors between countries (check out ENTSOE’s map of the European transmission network), and connecting offshore wind to mainland grids. And HVDC has long been touted as a decarbonisation tool in the US—to connect wind farms in the Midwest to load centres on the coast, or to connect grids’ solar output to different time zones—but the fractured nature of grid planning has limited it’s deployment.
✅ Advantages
Lower losses
DC is all active power and no reactive power (the part of AC that allows the current to flow)
Increased efficiency of HVDC over HVAC reduces losses from 5-10% in an AC transmission system to around 2-3% for HVDC.
Cheaper over longer distances: for transmission of 600 km or more, it becomes cheaper than AC (lower losses for all distances but the higher cost converters & substation equipment only amortised over longer distances)
More effective underground/under bodies of water since AC current experiences interference when buried, to connect offshore wind to a mainland grid for interconnectors e.g. from the UK to mainland Europe
Can be used to connect asynchronous AC grids
most countries run at a frequency of either 50 Hz (including the UK) or 60 Hz, and Japan has grids at each of these frequencies (because the US and UK each rebuilt one side of the island!)
Lower material requirements for DC because of skin effect due to Eddy currents in AC wires
❌ Barriers
Limited domestic supply chain (in US) due to low HVDC demand currently
Technologies to enable renewables penetration
Increasing the capacity of the grid is important, both using traditional T&D expansion and by employing the technologies discussed above. The following technologies are those that are required to enable full renewables penetration and bidirectional power flows. These are generally less mature technologies with further R&D and deployments required to be used at scale.
Distribution-level power flow control
In addition to the innovations at the transmission level, there is also significant progress in distribution-level power flow control technologies. These solutions are designed to address the increasing complexity and bidirectional power flows on the distribution grid, as it integrates more distributed energy resources (DERs) such as rooftop solar, energy storage, and electric vehicles.
At the distribution level one of the major challenges is the addition of new, large, DC loads–with EV charging as the main example—which affects the power quality, that in extreme circumstances, could lead to blackouts. A number of technologies are emerging to help to manage different aspects of the power quality, including power factor correction, voltage, harmonics removal and fault isolation.
Advanced transformers and power electronics
Transformers are used on the grid to step the voltage up—for efficient transmission—and down—for safer distribution and use. The working principle involves electromagnetic induction between two or more windings wound around a common magnetic core, where the ratio of the number of turns in the primary and secondary windings determines whether the transformer steps up (more turns in the secondary) or steps down (fewer turns in the secondary) the voltage. And whilst these traditional transformers are reliable and cost-effective, they are limited by their inherent unidirectional power flow, limited voltage regulation and monitoring capabilities.
Traditional distribution transformers are being replaced by more advanced, so-called solid-state transformers based on power electronics that provide features like voltage regulation, reactive power compensation, fault isolation, and bidirectional power flow capabilities. Startups like Amperesand (Singapore) and Solid State Power (USA) operating in this space.
ZCC portfolio company Ionate is developing their own Hybrid Intelligent Transformer (or HIT), that acts as a drop-in for existing transformers, but with added monitoring and dynamic control of the power quality of distribution grids. They are currently conducting their first field trials in Portugal and Spain with EDP
✅ Advantages
More monitoring and control
Faster response
Enable bidirectional power flows
❌ Barriers
High costs currently
Need for new standards and safety testing for power electronics
Inertia synthesis and control to enable an inverter-based grid
Inertia refers to the stored rotational kinetic energy in conventional power generators. This inertia inherent in large spinning masses like the turbines of thermal power plants and hydropower helps maintain the stability of the grid. Grid frequency (a measure of the balance of supply of electricity and demand) can drop if a large power plant or transmission fails. Inertia resists this drop in frequency, giving the grid time to rebalance supply and demand.
Inverter-based variable renewables do not naturally provide inertia. As these renewables replace conventional dispatchable capacity, system inertia is declining, raising concerns over grid stability and resilience. Replacing conventional generators with inverter-based resources has two counterbalancing effects. On the one hand, these resources decrease the amount of inertia available, but the fast response times of inverter-based technologies like Li-ion batteries allow for near-instantaneous frequency response, in turn reducing the need for rotational inertia. In an ideal grid with instantaneous response capabilities, inertia wouldn't be needed.
Grid-forming inverters
Most inverters today are “grid-following”. This means that whilst they can respond quickly to changes in frequency to alter energy output, they rely on an external voltage (from the grid) to “follow” the frequency, but they do not have black-start capabilities to restart the grid in the case of an outage or shutdown. In a world with very high renewables penetration and therefore fewer other resources that have black-start capabilities, this becomes a problem. The development of new “grid-forming” inverters—that can manage voltage and frequnecy independently—enable inverter-based resources to take a more active role in maintaining reliability and facilitating a purely inverter-based grid. It’s estimated that a 100% inverter-based grid could be supported if 30% of those inverters had grid-forming capabilities.
✅ Advantages
Grid-forming inverters can provide synthetic inertia, voltage control, and black start capability like synchronous generators. This enables stable inverter-dominated grids.
Fast frequency response from renewables and batteries can minimise the rate-of-change of frequency after disturbances, reducing the inertia needs.
❌ Barriers
Requires extensive modelling and field testing to develop advanced grid-forming inverter control paradigms.
Interoperability challenges integrating grid-forming capabilities with other grid assets and protection systems.
Switchgear
Switchgear is a critical component of the electrical grid, responsible for controlling, protecting, and isolating electrical equipment.
SF6-free switchgear
Sulfur hexafluoride (SF6) is a gas that is commonly used as an insulating medium in traditional switchgear. However, it is also a potent greenhouse gas with a global warming potential of 23,500 CO2e. There is a push to develop alternative insulating materials and technologies that can replace SF6 while maintaining the required electrical performance and safety. Examples of SF6-free solutions include vacuum, solid state insulators and new gas mixture. Nuventura are a Germany-based startup developing these alternatives.
DC circuit breakers
As the grid incorporates more renewable energy sources and high-voltage direct current (HVDC) transmission, the need for reliable DC circuit breakers becomes crucial.
Circuit breaker technology for AC is relatively simple, because AC current goes to zero every time the current changes direction, whereas DC the magnitude is constant, so breaking the circuit becomes more difficult as the current gets larger. Emerging solid state DC circuit breakers (e.g. Blixt Energy) aim to be smaller and more efficient than existing mechanical circuit breakers.
Undergrounding to overcome planning barriers to grid expansion
Undergrounding is the process of enabling cables to the laid underground rather than as overhead lines. This would circumvent some of the key barriers to grid expansion like NIMBYism and permitting challenges, but is currently much more expensive. Whilst the construction of underground lines will likely never compete with overhead transmission, lower costs could allow make underground competitive at a project level – the time cost of permitting delays and re-routing of overhead transmission could make undergrounding attractive enough. There is even controversial regulation in Germany that favours undergrounding instead of overhead power lines for new transmission
✅ Advantages
Safety: underground cables are less susceptible to extreme weathers events or deliberate attacks
Overcome NIMBYism: easier to permit underground cables along existing rights-of-way like motorways
❌ Barriers
Higher cost
Maintenance more challenging
The companies leading the charge
A nod to energy storage and microgrids
Energy storage is often cited as a critical technology to defer transmission and distribution upgrades. By placing energy storage systems near areas of high demand or constraint on the grid, they can be charged during periods of low demand and then discharged during peak periods to help meet the increased energy demand. This load-shifting can alleviate stress on existing T&D assets. Storage assets can also offer grid services such as frequency response to manage power quality challenges like inertia.
Microgrids are essentially self-contained grid in a limited geographic area that allows for additional resilience and takes power from local, distributed energy resources. They can be connected to the main grid or not, but the value proposition lies in additional resilience, lower transmission losses and less reliance on transmission upgrades, allowing for greater deployment of energy generation locally. Big load centres like hospitals and industrial users often have separate microgrids to ensure resilience to blackouts. Microgrids are also a growing phenomenon in emerging economies where transmission build-out is slower than renewables (mostly solar) deployment.
DC microgrids are a subset of microgrids where DC-based generation and use are connected together to minimise the losses associated with converting from DC to AC and back to DC. An example would be a large charging station where solar generation, battery storage and EV charging are all connected to a DC microgrid.
Other market and policy mechanisms can also help
But expanding and improving a system as complex and fundamental as the grid is not just a technological problem. There are other key market and policy mechanisms and that support deployment of the necessary technologies and speed up the rate of deployment.
Policy amendments to change permitting policies.
Grid access, planning and permitting. Permitting timelines for grid connections are long. Getting a UK grid connection was an 18 month average wait in 2019. In 2023 it’s 5 years, and over 40% of queueing projects have a connection date beyond 2030. But this is changing. In November 2023, Ofgem approved a proposal for the ESO to actively manage the connections queue to remove the blockers caused by speculative ‘zombie’ projects. And in Austria and the Netherlands permitting procedures for construction of generating assets and their connection to the grid is carried out in parallel to speed up deployment.
Different remuneration mechanisms
Ofgem’s regulatory framework RIIO (Revenue = Incentives + Innovation + Outputs) offers incentives for innovation and improvements.
New markets and/or market structures
There is currently strong debate in the UK around introducing locational pricing. Locational pricing provides locational and temporal signals to guide optimal siting of new generation capacity or new loads, in order to make better use of the existing grid infrastructure. This will reduce the amount of grid expansion and investment required overall.
And timing is critical: if grid stakeholders are too slow to act we will have a suboptimal grid with resulting in higher emissions than we should have, and higher bills than we we would like.