100 per cent integration of renewable energies
With the planned REGEES project, scientists are investigating how the electricity grid can also integrate renewable energy in the future while continuing to work safely. REGEES stands for optimum operating and control strategies for a reliable electrical energy supply system in Germany with a fully integrated infeed of renewable energy sources in a timeframe to 2030. To this end they are developing new operational management and control strategies, whereby if possible they want to fully integrate intermittently generated energy.
The distribution and transmission systems are already facing major challenges. Although a further expansion of renewable energies is planned, the increasing number of decentralised feed-in points is placing a burden on the electricity grid, which was conceived for just a small number of large-scale power plants. The resulting loads on the grid have not yet been scientifically investigated in all their facets and present a considerable challenge for the operators. One aspect, for example, are bi-directional power flows: with certain weather conditions consumers become generators. Depending on the topological distribution and the local weather conditions, this results in very different dynamics and volatility with respect to the infeed requirement situation.
At present, various measures can ensure that 100 per cent of the renewable energy is fed into the grid:
- Increasing the flexibility of conventional power plants
- Inter-grid level operational management with horizontal-vertical power flow optimisation, including a possible future overlay network
- Cross-grid utilisation of the various storage, control and flexibility potential
- Use of renewable energies to provide ancillary services (power, frequency and voltage control and reactive power provision), for example in the form of virtual power plants
In the REGEES research project, the scientists are developing and demonstrating approaches for coordinated grid operations management and control. The aim is to make optimum use of the centralised and decentralised control potential but also to observe the requirements of the energy market. A new challenge is presented, in particular, by the lower voltage levels in the distribution grids. Here there is still no continuous online monitoring for providing grid protection. The project partners want to not only establish the technologically sophisticated measurement and communication technology to be developed in the lower voltage levels but also operate it on all grid levels.
With the further expansion of renewable energy sources, a sufficiently accurate measurement of all grid levels is essential. By sharing schedules, this will enable grid operators to operate the grids directly affected in a coordinated and efficient manner. For this reason, the SCADA systems based on this approach must be capable of supporting the measurement and estimation of the status, including for previously unmonitored grid levels, and also be available as additional input variables for the newly developed cross-grid operation management and control strategy. The developed operational management concepts will be applied to this model and its impacts will be investigated.
The work is focussing on developing and closely investigating two operational management and control strategies:
- Coordinated TSO DSO network operations management
- Coordinated market-network management
The coordinated TSO DSO network operational management represents a new, innovative approach and includes the determination of the optimal horizontal and vertical power flows by taking into consideration all grid levels. Here the engineers are taking into account the predictable and decentralised intermittent infeeds and requirements as well as the current topology. The optimisation will then provide a 15-minute schedule for the grid connection points and controllable resources – such as storage systems – with a maximum use of renewable energy and a minimal down-regulation of decentralised infeeds according to Section 13 of the German Energy Industry Act (EnWG).
As part of the management strategy being developed, the experts are expanding the previous region-based approach with upstream and downstream networks. Here they are assuming that a new grid level in the form of an HVDC overlay network will be created on top of the currently existing 400-kV level. In addition, the respective processes for sharing schedules between the affected operators will also be defined.
Optimally marketing renewable energies within the grid restrictions
Aspects relating to the currently existing energy market have been disregarded in favour of the coordinated market-network management proposed in the project. This management approach aims to link requirements and aspects of the energy market with those of the transmission and distribution grid operation, whereby the networks will only be modelled abstractly in the form of replacement transfer capacities. This approach is aimed at optimally marketing renewables in the energy market within the network restrictions that need to be fulfilled.
The proposed approaches are intended to demonstrate how optimal grid operations management can be technologically and economically feasible with 100 per cent renewable energy. Based on simulations, the investigated approaches will be assessed in terms of their advantages and disadvantages, as well as any necessary regulatory adjustments, to enable the advantages of the various approaches to be utilised in future as part of a combined method.
Research results for economic and scientific purposes
The resulting findings will be economically and scientifically utilised. In addition to developing and strengthening knowledge and expertise, the project is aimed at developing future-oriented scientific topics. Possibilities for economic utilisation lie in the development of new methods and technologies for coordinated grid management.
As part of the research, two publications have already been presented at international conferences.
1) IEEE Energy Conference in Leuven, April 2016, from Fraunhofer IOSB-AST:
Zimmermann, T.; Klaiber, S.; Bretschneider, P.: "A Market System Operator as a new role to balance the distribution grid and to coordinate market and grid operations," IEEE International Energy Conference (EnergyCon), Leuven, Belgium, 4-8 April, 2016
This paper presents an approach for expanded market grid management. To this end, the role of the Market System Operator will be introduced and the ENTSO-e schedule registration system will be expanded. A traffic light system for distribution grids was also developed and integrated. The aim is to maintain a liberalised energy market as envisaged by the EU Commission, which does not hinder the objectives of the energy transition in Germany. The presented approach expands existing processes and roles without revising them. This strengthens the individual stakeholders and grid operators and improves their communication.
2) General Meeting of the IEEE Power & Energy Society in Boston, July 2016 by the Technische Universität Ilmenau:
Schwerdfeger, R.; Schlegel, S.; Westermann, D.: "Approach for N-1 Secure Grid Operation with 100% Renewables," IEEE PES General Meeting, Boston, USA, 17-21 July, 2016
This paper presents a concept for vertical grid management which, despite the high volatility of renewable energies, ensures a reliable electrical energy supply system. The technical challenges that this concept entails are highlighted. It is shown that the vertical grid management approach has a positive effect on N-1 security.
The work packages and project partners at a glance:
0 Project management (Fraunhofer IOSB-AST)
1 Requirement analysis (TU-Ilmenau)
2 Optimal vertical grid management (TU-Ilmenau)
3 Optimal horizontal grid management (Fraunhofer IFF)
4 Virtual power plant with 100 per cent renewable energies (OvGU)
5 Coordinated market-grid management (Fraunhofer IOSB-AST)
6 SCADA/EMS (Siemens AG)
7 Validation, analysis and summary (Fraunhofer IFF)
01/2015 – 12/2017
Am Vogelherd 50
Section 13 EnWG
Section 13 of the German Energy Industry Act (EnWG) regulates the circumstances under which the transmission network operators are authorised or obligated to prevent hazardous situations or grid disturbances. They can achieve this by deploying grid-related measures such as network switching or by deploying market-related measures such as the use of balancing power.