The deployment of renewable resources and flexible resources in medium and low-voltage distribution systems has generated interest by the academic community and practitioners for designing and implementing “flexibility” platforms in recent years. The potential benefits of such platforms are numerous and a large variety of designs can be considered.
Importantly, flexible platform designs should account for the specificities of different systems, especially when it comes to short-term flexibility and TSO-DSO coordination possibilities.
The Norwegian transmission grid tends to be more constrained than other control areas, and therefore requires extensive congestion management. The Norwegian system is also characterized by a large share of hydro generation, with no significant ramp constraints. Therefore, a limited need for fixing production should be scheduled well in advance of real-time.
The perspective of combining congestion management with balancing activation has already been analyzed in a previous study.
Given the increasing proliferation of resources at the distribution system level, Statnett (Norwegian TSO) would like to be in a position to mobilize decentralized resources for “flexibility”, i.e. for balancing activation as well as for congestion management.
The question is how this can be achieved without causing problems in the distribution networks since Statnett does not have full visibility over these grids.
In this study, we first analyze several pilot or commercial projects with similar objectives (Enera, Gopacs, Nodes, Piclo, Cornwall, Soteria, Coordinet, Smartnet). A key observation is that these projects typically segment balancing and congestion management, rather than considering them as an integrated process. This is why our study has focused on solutions in the mFRR timeframe, where mFRR-type bids from assets at transmission and distribution grids can be concurrently activated for two purposes: restoring the balance and managing congestions.
The analysis highlights the benefits of a “hierarchical approach”, where each DSO makes use of an “Aggregation-Disaggregation Service (ADS)” to compute a so-called Residual Supply Function (RSF) which describes the least-cost way in which the given distribution subsystem can deliver – while respecting all the provided grid constraints – a certain aggregate upward or downward action at the point at which the distribution system is connected to the higher-level voltage network. This information is then shared with the TSO, which can activate them similarly to other mFRR bids, without risking causing problems in the distribution grids.
The hierarchical approach sets forth in the report has key valuable features:
- it is highly scalable: each DSO manages its own market and grid data, and shares with the TSO the relevant economic information in an aggregate and compact form,
- Data handling allows a clear separation of the roles and responsibilities,
- It is versatile and allows multiple variants: different settlement/pricing schemes, price sensitivities to resolve congestions, gradual implementation, …
- It is compatible with the upcoming European Balancing platform (MARI)