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Secure supply

At TenneT, our mission is clear: to keep the lights on. Making sure that more than 41 million people across the Netherlands and Germany enjoy uninterrupted access to electricity is the foundation of our business. By investing in new assets, performing necessary maintenance and making sure that we are prepared in case of unforeseen events, we aim to ensure security of supply for society. 

In today’s always-on world, electricity users assume they have power available at their fingertips – never more than a power outlet away.

We have worked hard to meet this expectation on every step of our 20-year journey. This is a complex task, which involves operating, maintaining, upgrading and expanding a network of approximately 23,000 km of high-voltage lines and cables.

In addition, we must transport electricity from a growing number of renewable energy sources (RES) that are, by nature, more difficult to predict and supply. If the wind doesn’t blow in one area or the sun doesn’t shine in another, the market must be ready to flexibly shift electricity from one source to another to meet demand.

Meeting these expectations is not only core to our mission to deliver security of supply, it also links to the wider ambition of SDG 7 – Affordable & Clean Energy. SDG 7 links to TenneT’s role in contributing to national and international climate agreements, as we want to facilitate access to affordable, reliable and modern energy services.

This goal, which recognises a basic need of modern society, is central to TenneT’s role and we are committed to supporting it by operating our grid with maximum availability. Our work to build cross-border electricity transport capacity is an important part of this endeavour, growing our access to supply and thereby helping to lower electricity costs for end-users. To ensure that we are able to secure supply, we are continuously maintaining our grid and monitoring its availability. When an unexpected outage occurs, we report and investigate its nature and impact so we can resolve it as quickly as possible and learn from it to prevent – as far as possible – it re-occurring in the future.


Grid availability201820172016
Grid availability99.9988%99.9986%99.9999%
Energy not transported (MWh)1,1841,07259
Grid availability94.50%97.80%92.00%

1 The 2018 figures are presented based on the former definition. When applying the updated definition, the grid availability remains unchanged (99.9988%), the number of interruptions will be 17 and the energy not transported will be 1,244 MWh

Our onshore security of supply rose slightly to 99.9988% in 2018. Although we work hard to secure supply of energy at all times, several outages occurred that contributed to this result. These included a notable outage in August, in the Tilburg area in the south of the Netherlands, where at least 100,000 households and hundreds of companies lost power for at least 22 minutes and some up to one hour. Another incident occurred in April, in the Amsterdam area. The outage was resolved within a couple of hours, however due to knock-on effects at Schiphol, the main airport in the Netherlands, the impact was visible throughout the next day. Starting 2018, we have updated our definition of interruptions to create further alignment in the Netherlands and Germany. This now includes interruptions of supply, which is not only related to end-use consumers, but also to energy suppliers when they are unable to deliver energy to our grid. 

Expanding, modernising and future-proofing our grid helps us avoid outages as much as possible. TenneT assesses its investments each quarter, adjusting plans and actions as necessary. In 2018 we invested EUR 2.3 billion in expanding and maintaining our grid. We can face delays in this important process for example when approval processes take longer than expected or when late delivery of materials puts projects behind schedule. This occurred in 2018, when the summer drought made the water level in parts of the Rhine river too low for transport. We experienced a notable setback in October 2018 when we terminated the Wintrack II contract, involving the construction of new high-voltage pylons running on two tracks: Eemshaven-Vierverlaten and Borssele-Rilland. This contract was with the Dutch consortium Heijmans Europoles B.V. (HEP). 

Technical data201820172016
Total circuit length (km)22,86222,85722,637
Overhead lines (km)18,72518,97418,830
Underground cabling (km)4,1373,8833,724
Number of substations462462458
Number of HVDC stations181616

With respect to securing supply through new projects, work is progressing well on both the Mittelachse line and the Westküstenleitung line in Schleswig-Holstein. These are important projects for the energy transition. In the future, the connection will transport this renewable electricity to energy users in southern Germany.

DolWin3 is also a significant step in the development of the offshore grid and the North West European market. This 160 km DC connection for offshore wind power became operational at the end of 2018 and is the third in the DolWin cluster. It connects wind farms in the southwestern part of the German North Sea to the onshore transmission grid supplying more than one million households with clean wind energy.

Linking the wind energy hubs of the north with consumption centres in the south is essential for the success of the energy transition in Germany. This will be especially true after 2022, when nuclear power plants will stop generating electricity in Germany. That is why TenneT is working on major projects such as SuedLink and SuedOstLink helping to future-proof the German energy infrastructure. 

We reached a milestone in 2018 when the jacket of TenneT’s first offshore transformer platform for the Borssele offshore wind farm was successfully installed. The project will see two connections of 1,400 MW, come into service in 2019 and 2020. Four AC cables will run from the platforms to the mainland, routed via the Western Scheldt river. Coming ashore near the existing high-voltage substation at Borssele, they will connect to the substation via underground 220 kV cables. The onshore Borssele substation will be expanded to create extra room for the transformers required to convert the voltage level from 220 kV to 380 kV. The national 380 kV high-voltage grid will then distribute the wind energy to households across the country.

In September, TenneT signed an agreement with Enecogen for the provision of a 'black-start' facility at the Enecogen gas station in Rotterdam-Europoort. In the event of a black out, this emergency provision can be used to put the high-voltage grid back into operation. TenneT now has three such facilities available in the Netherlands, contributing to a stable and reliable energy supply. In Germany we continue to work on facilities to secure and restore supply in case of local grid situations. By law, we are permitted to assign third parties to build and provide these facilities. We are currently reaching an agreement for this purpose with Amprion and TransnetBW in Bavaria, Baden-Wuerttemberg and South Hesse, with the intention to finalise in Q2 2019. We have also contracted additional reserves in southern Germany and outside of Germany.

Looking to the future, when wind and solar generation will account for higher amounts of electricity feeding into the grid, TenneT believes that the use of green hydrogen will be an important addition to our energy system. Produced through the electrolysis of water by renewable electricity, green hydrogen is carbon-free and is considered alongside other renewables in the Dutch Climate and Energy Agreement. As it can be stored, green hydrogen is a flexible controllable energy source, which will benefit security of supply.

Our ongoing goal is to provide a secure and reliable supply of energy. We aim to do this as cost efficiently as possible to provide affordable electricity. This is why we invest in innovation as we believe this will make our grid more resilient and futureproof providing long-term value for society. However the current reimbursement structure does not always compensate for innovation, especially with respect to IT driven solutions, which we believe will benefit the security of supply. In this context, we need to balance the financial health of the company with the cost of innovation projects that will be beneficial for society in the future.

Also, when planning and tendering our projects, we acknowledge that increasing standards we expect from our suppliers are a challenge. However, as we feel that we are a company that wants to meet these standards, we want to help our suppliers and reach the level we desire, rather than lower the bar for ourselves.


Secure supply
1The investment portfolio leads to high workload along the entire supply chain. TenneT faces scarcities in the supplier markets caused by a strongly increasing market demand on power transmission components and especially for overhead-lines and cables. With this high workload we also see a lack of qualified staff for TenneT and its suppliers, which we see as a challenge related to our investment portfolio. This could result in a delay of projects.We settle framework agreements, bulk orders, enforce standardisation, increase storage capacities, improve demand forecasts, actively support development of new technologies (e.g. 525 kV DC-cables) and look for alternative supplier and service providers worldwide. Furthermore, we extend employment of external project management service providers to staff construction projects in the onshore grid. To mitigate a lack of internal resources, we pro-actively perform analysis to have an adequate succession plan of our staff.
2Due to faster RES integration and increased activities on our existing grid reducing the outage planning is essentialWe continue to develop new and innovative ways to further improve our way of working to be able to secure supply of electricity. TenneT had some successes in 2018 in keeping systems up during maintenance, thanks to innovative uses of technology. For example, when we discovered that a high voltage cable buried under the seabed of the North Sea was beginning to surface due to sediment movements of the actual seabed, our engineers successfully managed to re-bury them whilst the cable remained in service, thereby minimizing the down-time to a short interruption that was required for technical reasons. TenneT has also executed a pilot project with a spin-off company of ETH Zürich to investigate if a four-legged robot can execute inspections in support of unmanned phases of the offshore platforms.
3The low carbon emission ambition resulting in increasing RES integration creates new challenges related to system balancing, as RES output predictions prove to be more volatile due to fluctuations in the real time weather conditions.Being able to better predict weather conditions and translating this properly will become increasingly important. Unlocking flexibility and investing in broad spectrum predictive RES output modelling in a progressive market design is essential. With this we can better inform and challenge other market parties in system balancing.

Strategic risks

Most relevant risks regarding security of supply are related to the ageing of infrastructure assets, resource constraints in the supply chain, scarcity of qualified personnel, uncertainty in energy markets and politics terror/cyber-attacks as well as major delays of large infrastructure projects. However, there are also opportunities, particularly in the use of digitalisation and the development of new technologies.

The likelihood of unplanned outages increases as TenneT’s infrastructure assets grow older. The growing share of renewable electricity can also add to the risk of outages; as wind or solar-generated energy is less predictable, it is more challenging to shut down parts of the grid to perform maintenance works. To mitigate this risk, additional resources are made available for maintenance works and we are increasing the efficiency and flexibility of our maintenance programme by monitoring and simplifying internal processes.

In today’s cross-border energy market, security of supply is enhanced by the interconnectivity of the European transmission grid, from Portugal to Turkey and from Scandinavia to Italy. However, misalignment in the energy policies of individual European countries – such as stalling plans to invest in nuclear power, stopping the development of coal or lignite plants, or increasing the development of renewables – have a significant impact on the entire European grid. As such, the challenge of dealing with European grid issues becomes more of a daily occurrence, especially as the further integration of renewables and lower availability of conventional power production increases the likelihood of critical situations. This is particularly true during autumn and winter. This requires international alignment of political targets. TenneT works towards this by engaging in and providing transparency in political discussions.

Our planned investment projects all involve a high degree of organisational complexity. This can include communicating with a large number of stakeholders, assessing different technological options, routing options, interdependencies of work packages between different projects and challenges in the political environment. Delays in licensing (especially necessary permits from the authorities) as well as challenges arising from the use of innovative technology (HVDC, Wintrack-II respectively) can also throw a project off schedule. TenneT works to mitigate these risks by communicating transparently with regional stakeholders, working closely with authorities, enforcing high quality standards and closely monitoring its suppliers and deliverables. Additionally, TenneT continuously works to optimise its organisational processes , including lean decision making processes, an emphasis on employee training and use of probabilistic schedule analyses.

Nonetheless, technology plays a crucial role in mitigating risks around security of supply. In particular, TenneT sees an opportunity in using digitalisation to improve the utilisation of the grid, without increasing black-out risks. To this end, we are exploring the potential of big data to improve our capacity to predict the weather and assess levels of consumer demand. Sophisticated data analytics can also help us determine the condition of our assets and reduce demand on the grid at peak times by connecting decentralised batteries together (so-called “peak shaving”). Owning, or at least having real-time access to, specific data while complying with the requirements of the EU General Data Protection Regulation (GDPR) certainly presents risks for TSOs. It also means high requirements for IT skills and capacity, requiring data to be processed in real time.

TenneT takes the possibility of a severe outage resulting from a terror or cyber-attack very seriously. We regard the risk of a politically-motivated attack, either government-backed or non‑state cyberterrorists, higher than “usual” computer fraud crime. Hence, a successful attack cannot be ruled out entirely, despite us having physical and digital prevention measures in place that are continuously assessed, optimised and tested. To this end, we develop, align and carry out contingency plans together with national authorities. In Germany, TenneT achieved ISO27001 certification in 2018.


Maintaining a reliable and safe electricity supply by improving and maintaining the high-voltage grid is only part of the challenge. As society demands more renewable electricity, all grid operators face the challenge of maintaining security of supply in a more volatile energy environment.

On the 26th of January 2019, the coal commission presented a consensus on the phase-out of coal fired power plants in Germany. The main cornerstones are a 12.5 GW reduction of coal-fired power plants by 2022, a further reduction of 13 GW until 2030 and a complete phase-out by 2038. This might influence our grid extension plans until 2035 and beyond.

As we advance with the energy transition, the task of maintaining this balance becomes more complex and involves more market players, including large generators and small-scale domestic producers. These players now actively participate in an increasingly decentralised electricity market.

In this scenario, TenneT – along with other grid operators – needs more sophisticated solutions and flexible commercial agreements to balance electricity demand and supply. Existing market designs can become barriers to innovation and progress and may need to be changed. Significant grid innovations will be essential to prevent energy shortages and realise society’s green energy ambitions.

Case study

This is one of our most recent offshore projects taken into operation. This offshore converter platform connects renewable energy from wind farms through a 135 km long cable to the onshore grid. The development of these offshore projects is essential to realise climate ambitions. Construction of this platform started in 2012 and with a transport capacity of 916 MW, DolWin2 has the potential to supply more than one million households with clean energy per year. 

As we aim to invest a significant amount to expand and maintain our grid, we are aware that our impact goes beyond the financial 'bottom line'. Our assets, have both positive and negative impacts for society. To gain more insights of these impacts, we have monetised environmental, social and economical factors related to DolWin2. Our case study has focused on specific steps in the value chain, from raw material extraction to the operation phase of this project. 

We realise that this case study is a part of the first steps we are taking to gain insights on the True Value of our operations. In recent years, we have performed similar pilot projects for our onshore operations. That is why we have chosen an offshore project for this year's case study. We aimed to collect data for the most material impacts of each phase of DolWin2 and monetise these impacts with a Euro value, to have one common denominator at the end of this case study. 

The results of this case study show that the main impact of DolWin2 is environmental. Negative environmental impacts are mainly related to material extraction and constructing the platform. However, by realising this project, we are able to avoid carbon emissions that otherwise would have been emitted by less sustainable sources such as coal plants. This case study shows that next to the economical costs and benefits, the true value of this project lies in the environmental impact this project has for society, 

We acknowledge that impact reporting is still an area that is under development. That is why we work together with other companies in the Dutch infrastructure sector and MVO Nederland in the 'Groene Netten' coalition to take next steps and create a common language. This will help our stakeholders gain more insight into the impacts we as companies in this sector have. It can also help us internally in our decision-making process. More details on this case study can be found on our website.