e-Highway 2050: Recommendations about potential solutions to address challenges in long-term grid planning

Challenges
Which improvement, specification of new tools and further research are needed to address long-term planning over large transmission systems based on the e-Highway2050 grid expansion methodology formulated as an optimisation problem?

Background and assumptions
Long-term transmission planning over large power systems, such as the European transmission network, is a very large and complex problem and today, any national transmission system in Europe is planned using expert judgement.
The e-Highway2050 project defined a new methodology where long-term planning is formalised as an optimisation problem, and at specifying new tools. The process followed by the developed methodology is reminded in Figure 1.

Figure 1 – Methodology proposed in e-Highway2050, WP8

1.      Key findings of the long-term Grid Expansion planning methdology
Reduction techniques
The problem may be reduced in several ways before being tackled using optimization: from time and stochastic reduction to network reduction. First, snapshot selection techniques were investigated in the project to reduce temporal and stochastic complexities. Regarding spatial complexity, network reduction techniques have been developed. However, the equivalence between the expansion in the reduced network and the detailed (nodal) network should be further researched. Finally, the set of network reinforcement alternatives to be explored may also be reduced, focusing on the most promising ones and discarding others that do not make sense from a techno-economic point of view.  Further research could study the impact of the reduction in a deeper way than the one that could be included in the scope of the project.

Power flow calculation
Using a DCPF seems better suited for TEP. Only approximate calculations for losses can be considered manageable in this context. Developing efficient ACPF solvers is extremely interesting, although their direct incorporation to automatic TEP is difficult. Besides, adequately representing the flow controlling features of new technologies may prove to be very valuable to increase the efficiency of expansion planning solutions computed.

Reliability/Network maintenance
The incorporation of reliability or line maintenance decisions using classical techniques can lead to unmanageably large problems. The project recommends the use of simplified, heuristic procedures to this aim whose results can be introduced as constraints in the optimization problem. Further research could lead to more sophisticated, efficient heuristics.

2.      Overview of the recommendations about potential solutions to address challenges in long-term grid planning 

A set of recommendations for each of the six steps of Figure 1 is proposed in [1]. They can be split in three types:
- Improvements of existing tools and methods: they consist of incremental improvements of existing solutions and tools easy to implement, and are generally pre or post processing.
- Specifications for new tools: industrial IT solutions must be developed but we have a good idea of the specifications for these new tools, thanks to the prototypes developed during the project. There is a moderate risk associated to scalability issues and computation times.
- Recommendations for future research: during the project we identified some open questions on some critical aspects and we have proposed heuristics solutions, however more R&D could be useful to try to have better solutions.

Table 1: Overview of the recommendations on the transmission expansion planning methodology

3.      Conclusions

This work constitutes the final stage of the development of an enhanced network expansion planning methodology by the e-Highway-2050 project, supported by the EU Seventh Framework Programme.

References

[1] C. Pache, P. Panciatici, RTE; S. Lumbreras, F. Echavarren, L. Sigris, Comillas. Deliverable D8.7. of e-Highway2050 project: Recommendations about critical aspects in long-term planning methodologies. December 2015