HVDC technology is being increasingly deployed owing to its controllability and efficiency in transporting electrical energy over long distances. The shift towards renewable, but often remote, dispersed and variable means of electricity generation imposes a very different operation profile on the transmission infrastructure, and hence these features of HVDC assets are set to become essential in delivering the energy transition.

A large proportion of renewable generation, especially offshore wind, takes place far away from the load centres where this energy is utilised. Therefore, the electrical network needs a sufficient transmission capability to unlock the installation of large-capacity renewable resources and HVDC transmission is well suited for creating such energy highways.

In the UK, multiple HVDC projects are earmarked for the purpose of enabling the installation of higher wind generation capacity, such as the National Grid and Scottish Power (SPEN) Eastern Green Link (EGL1) connecting the Torness area in East Lothian to Hawthorn Pit between Murton and South Hetton in County Durham. This 2 GW, £1.2bn subsea HVDC link is one of four planned to improve the transmission capacity between windy Scotland and power-hungry England.

As more wind is developed and all of the low-hanging fruit connection points and shallow areas close to shore are exploited, distances inevitably have to get longer to the point where HVDC is the only technically and economically viable solution for integrating such remote resources to the AC (alternating current) network.

The variable nature of the dominant renewable generation methods also means much larger fluctuations in geographical power availability. Controllable HVDC transmission interconnectors will be essential to allow energy trading between generation-rich and generation-poor areas, and reduce the need for large volume online generation reserves.

These three applications, embedded links, renewable generation and network interconnections, will drive increasing demand for HVDC installations. Recent analysis suggests the global HVDC market is expected to grow year-to-year by 9% on average between now and 2028.

However, accelerating market growth presents several challenges for all – original equipment manufacturers (OEMs), developers of wind projects, and the owners/operators of the associated transmission assets.

Recent analysis suggests the global HVDC market is expected to grow year-to-year by 9% on average between now and 2028.  

The path to standardisation
The HVDC marketplace is changing massively. With only a few manufacturers producing HVDC equipment, the three leading Western OEMs – Hitachi, Siemens Energy and GE – all have rapidly increasing order books to a point where not only more scaling up is required, but more efficiency too.

Despite successful efforts to find and train more staff to meet the resource demand, there is still a shortage of skills, knowledge and experience across the sector for clients and OEMs alike.

Conscious of their limits, manufacturers are becoming increasingly discerning about which projects they engage with. Confidence in a project’s profits is crucial. If a project is likely to be cancelled due to unsecured financing, or the technical specifications are too ambiguous or prescriptive in their requirements, or if the risks imposed by the delivery schedule or the contractual terms are too high, their engagement in the bid will be adjusted accordingly. No bid decisions and/or punitive bids are now more commonplace.

Manufacturers are looking to increase output with standardisation of products. The trend to date for HVDC projects had been bespoke solutions that pushed the edges of technology in some form or other, but which were labour-intensive and time-consuming due to the high re-design factor. Now, the technology is reasonably well developed and de-facto standards are settling out in DC voltage, power rating, configuration, control features, valve architecture and contractual arrangements.

Right now, larger serial projects are taking OEM’s focus over smaller individual or more piecemeal developments. This is partly due to the investment cost of highly technical bids, which is expensive, but mainly and more so to benefit from clear efficiencies through the engineering, procurement and construction of the project, the reduction in risk and the quality improvements that can be obtained by running a batch of ‘same spec’ links through design, factory test, commission, on repeat. The objective here is to do more with the resources that we have.

Standard solutions are only partially possible as there is and always will be an element of bespoke engineering in every project. The responsibility for widening the standardisation scope largely relies on the market stipulating consistent requirements for HVDC equipment capability and functionality.

It is important that buyers, such as transmission utilities, focus on formulating functional-level specifications without dictating technical solutions beyond what is required for meeting grid codes and security of supply at the network connection point. In such a framework, OEMs have the freedom to develop their own standardised solutions within the HVDC station boundaries that are built around their technology and design know-how. This ultimately leads to more cost-effective and robust assets.

A good example comes from the Dutch-German transmission system operator TenneT. Its ‘one fits all’ programme was developed in response to the ambitious offshore wind targets of Germany and the Netherlands – 30 GW and 22.2 GW, respectively, by 2030, and generation capacity will require a series of 2 GW, 525 kV HVDC links to be developed.

The 2 GW scheme features an approach that aims to foster harmonisation across all levels –

technology, design, and even using the standard form FIDIC (International Federation of Consulting Engineers) contract structure. Between 2028 and 2031, TenneT and its partners will commission 14 HVDC links, eight in the Netherlands and six in Germany, using this unique transnational model with the potential to become a European template for offshore grid development.

Industry bodies like CIGRE (Conseil International des Grands Réseaux Electriques) are also trying to drive the body of knowledge forwards. There are approximately 260 CIGRE Working Groups, some of which are very specific to driving HVDC technology and its various applications to bulk power systems.

As market needs evolve and new technologies become available, there will always be a need for the standards to change and keep up. As an example, cyber security is a growing area of disconnect and risk in the HVDC marketplace as expectations in level/method of protection vary wildly around the globe, with competing and evolving standards in a rapidly changing field.

Considering the volume of the booming European offshore wind market around the North Sea, multi-terminal HVDC schemes promise better asset utilisation and availability compared to traditional point-to-point connections. This inevitably leads to multi-vendor projects, where HVDC stations delivered by different OEMs will interact directly within a common HVDC transmission infrastructure. A new level of legal, commercial and technical standardisation will be required to facilitate all the new interfaces that will open under such a market paradigm for all project delivery stages.

Multiple efforts are being made, such as the InterOPERA project under the EU’s ‘Horizon Europe’ framework, to pave the way.

The asset transfer challenge
Other areas that will benefit from greater standardisation are operations and maintenance. UK regulations mean a developer can build and commission a wind farm, but the transmission asset must be divested to an offshore transmission operator. Several groups currently operate around the UK, known as Offshore Electricity Transmission Operators (OFTOs). One of the reasons for the development of this structure is to reduce operations and maintenance (O&M) costs.

An important enabler for O&M is for the O&M staff to understand the asset. However, where each asset is unique and bespoke, this knowledge is best gained through the design phase, factory testing of the control systems and all other plants, through to commissioning.

Given that HVDC assets are expected to have a life of approximately 40 years, there is a significant likelihood that these assets will change hands over such a long period. Transferring the already built and commissioned asset effectively excludes new owners from the vital ‘ground floor’ training for O&M. This can leave those purchasing the asset vulnerable.

Purchasers are almost coming in blind on O&M, so they are a lot more reliant on the existing provider, especially for the converter and control systems. That’s where much of the O&M cost lies and is one of the significant challenges compared to a comparable AC link.

Larger transmission entities like RTE, utilities with a fleet of HVDC and appetite for more, can develop teams with a deep skills base, retain staff who have been in at the start, and have multiple assets to keep their skills honed. This presents opportunities to hold on to staff and bring together a common control room that will serve numerous links, with staff being able to work on all of the links.

For smaller owners, such as those with a single link serving a large offshore wind farm, that is not possible. It leaves those owners generally relying on the OEMs for long-term O&M services, which is both a commercial risk and a significant cost.

Although sales of HVDC links have to date been moderate, merchants are now developing HVDC systems that are more likely to be sold once they are operational. As those assets reach the market, potential purchasers must understand the role of due diligence and thinking forwards when considering elements like O&M. Due diligence of HVDC assets is just starting in the UK and will present one of the most challenging asset classes to get right.

Where continuity of O&M staffing is unavoidably broken through the sale of an asset, there needs to be considerable thought, effort and investment put into rebuilding and maintaining the capability.

Standardisation will certainly help here, particularly for O&M. It is likely that as standard systems emerge and become commonplace, training and transferrable skills become more readily sourced, and in-house staff who can execute O&M across a range of assets can be developed. For the future, we need to further develop our standard models and appropriate governance systems with the input of Ofgem, OFTO’s OEMs and other regulatory authorities. These systems must enable joined up thinking such that owners and operators can reap the benefit of the design, testing and commissioning phases of the project to inform the O&M effort.

Until that happens, though, working with experienced partners who understand HVDC asset operations and can consider the pitfalls and opportunities over the long-term life of the asset can help manage the high O&M costs and risks.

Looking ahead
HVDC assets are rapidly scaling up, and rightly so; they are a crucial element of our net zero ambitions. At the same time, a more fluid and commercially driven industry raises significant opportunities for efficiency and cost savings. But it’s also critical that market players don’t lose sight of the practical realities of operating and maintaining HVDC systems when considering a due diligence exercise.

Developers must ensure they are attractive on several fronts to secure the necessary OEM engagement and, unless everything is in place, it will not be possible to progress the project. Planning and executing an HVDC project scoping and procurement exercise to the highest standards is mission-critical, as is early engagement with the supply chain, regulator and transmission system operator, and keeping an open mind and exercising restraint in drawing ‘must have’ lines in and around the specification, favouring the reasonable risk sharing, the prevailing standard OEM offering and leveraging the economies of scale – it being cheaper by the dozen.

Standardisation is organically happening right now in the marketplace across all areas – power carrying capacity, voltage, configuration, interfaces and interoperability. This shift will present many efficiencies and positives throughout the project lifecycle, increase global HVDC production capacity and reduce risk for all.