The war between Russia and Ukraine is a turning point for Europe and for the European energy supply system. The pressure to consistently restructure our energy system in Europe is growing ever stronger, and the shared search for solutions is more important than ever. To reduce the dependence on fossil fuel imports (at least in Germany) as quickly as possible and to implement the required climate protection measures at full speed, the build-out of renewable energy must be accelerated considerably. The goal of the German federal government is to cover at least 80 percent of Germany’s power consumption with renewable energy by 2030. By 2035, this figure should be nearly 100 per cent – in other words, we have exactly 13 years left.
It is necessary to pull out all the stops when it comes to technological development and innovation.
As a transmission system operator (TSO), we play a key role here: We make it possible for the increasing volumes of renewable energy to be integrated into the system, making them available to society and industry. Due to the development of wind power in the North Sea, the demand for transport to the centres of population and industry is growing. Faster grid expansion is the order of the day. But even another 380 kV AC grid expansion (alternating current) does not by itself live up to this challenge either on a technical level or in terms of public acceptance. New concepts are therefore urgently needed for the integration of renewable energy. The following innovations in the transmission system grid are particularly promising:
1. 525 kV DC cable technology
Until recently, 320 kV DC cables (direct current) were still the state of the art. As a result, all offshore wind farms built so far in Germany are connected to the AC grid via corresponding converters and cables. Now the new German government intends to speed up the expansion of offshore wind farms in the North and Baltic Seas from the current 8,000 MW to 30,000 MW by 2030. The new 525 kV DC cable technology enables transmission capacities of 2 GW per system. The German TSOs are therefore planning to consistently use this technology for all newly approved offshore connection systems and onshore DC lines. This will allow a significant reduction in the number of required offshore grid connection systems compared with use of the established 320 kV technology. This means less space is required, while reducing the impact on natural landscapes and lowering costs.
2. Multi-terminal hub concepts
So far, all DC lines in the world have been designed as pure point-to-point connections. An initial pilot installation in Asia has shown that reliable operation with more than two converters is also possible. At least on a small scale, this opens up the possibility of linked DC systems as long as the consequences of a cable fault do not exceed the limits in terms of balancing capacity in Europe (3000 MW max. permissible power shortfall) and the power load supportable by the AC grid (2000 MW in Germany). A DC multi-terminal hub concept on the coast of Schleswig-Holstein has been confirmed for the first time in the current grid development plan for Germany. Two offshore connection systems will be connected to a single converter on the coast and to a continuing direct current line to Brandenburg. Compared with pure point-to-point connections, this eliminates two converters in the Heide coastal region. At the European level, research projects for standardising the converters have been announced so that systems from various providers can be used together.
3. Wind power hubs for hybrid offshore interconnectors
Currently, TenneT transports offshore wind power via long DC cable connections to the coast, from where – in the worst case – it is hub concepts offshore as well. A cable system from Norway would spare the detour to the coast of Germany and then only have to be run to the offshore wind farms. When the wind is calm and power prices are high, hydropower could be exported to Germany via the offshore connection systems, and when the wind is blowing – making for excess electricity in Germany – the wind power could be exported directly to Norway. However, implementation of this concept still faces European legal obstacles that assign priority to wind power over international energy trading. Questions concerning an offshore bidding zone must also still be answered.
4. DC circuit breakers for meshed DC overlay grids
As already described, linked DC systems are only possible on a small scale – since 525 kV DC circuit breakers do not exist yet that could safely divert a fault in a cable section. ABB in particular has made tremendous progress on the development of 320 kV DC circuit breakers, demonstrating what is possible. The full potential for cost savings and targeted shifting of the load flow across Europe via a DC overlay grid can only be realised once 525 kV DC circuit breakers are available. To resolve this chicken-and-egg dilemma (in other words, the industry will only finalise the development of these circuit breakers once a demand for them is expected), the German TSOs are planning to directly include circuit breakers in the invitation to tender for the planned 525 kV multi-terminal structures – meaning such will be designed as overlay-ready.
5. Innovations in system management – InnoSys2030
Alongside the efforts to establish a DC overlay grid, research projects are currently in progress to increase the capacity utilisation of the existing AC grids. Such grid operations equipment will be installed in the German grid in the coming years – though the corresponding optimisation methods for control by system management are still under development. Furthermore, the batteries that will be available in the future thanks to electromobility and photovoltaic systems for storage will offer great potential for rapidly available flexibility. This will permit a switch from the current practice of preventive redispatching (i.e. the grid is only loaded up to about 80 percent as a precaution in case of a potential fault) to a corrective redispatching approach. In the future, it will only be necessary to initiate measures to reduce the load flow when an actual fault has occurred. This means that utilisation levels near the 100% limit are conceivable during normal operation, and the redispatch costs can be lowered significantly. In order to develop secure methods for control and grid analysis in the control centres, TenneT will install large batteries (so-called grid boosters with 100 MW capacity) in the transmission system grid as an initial step starting in 2023. The processes for SMART control of the small-scale flexibility options should then be available by 2030.
In order for the TSOs to continue offering Germany one of the most secure grids in the world – with a grid availability of 99.9999 per cent – it is necessary to pull out all the stops when it comes to technological development and innovation. New innovations are essential for keeping pace with the growing transport demand and overcoming the challenges of the energy transition.
