Flexibility needs in the future power system

Power system flexibility relates to the ability of the power system to manage changes. Solutions providing advances in flexibility are of utmost importance for the future power system. Development and deployment of innovative technologies, communication and monitoring possibilities, as well as increased interaction and information exchange, are enablers to provide holistic flexibility solutions. Furthermore, development of new methods for market design and analysis, as well as methods and procedures related to system planning and operation, will be required to utilise available flexibility to provide most value to society. However, flexibility is not a unified term and is lacking a commonly accepted definition. Several definitions of flexibility have been suggested, some of which restrict the definition of flexibility to relate to changes in supply and demand while others do not put this limitation. The flexibility term is used as an umbrella covering various needs and aspects in the power system. This situation makes it highly complex to discuss flexibility in the power system and craves for differentiation to enhance clarity. In this report, the solution has been to differentiate the flexibility term on needs, and to categorise flexibility needs in four categories: Flexibility for Power: - Need Description: Short term equilibrium between power supply and power demand, a system wide requirement for maintaining the frequency stability. - Main Rationale: Increased amount of intermittent, weather dependent, power supply in the generation mix. - Activation Timescale: Fractions of a second up to an hour. Flexibility for Energy: - Need Description: Medium to long term equilibrium between energy supply and energy demand, a system wide requirement for demand scenarios over time. - Main Rationale: Decreased amount of fuel storage-based energy supply in the generation mix. - Activation Timescale: Hours to several years. Flexibility for Transfer Capacity: - Need Description: Short to medium term ability to transfer power between supply and demand, where local or regional limitations may cause bottlenecks resulting in congestion costs. - Main Rationale: Increased utilisation levels, with increased peak demands and increased peak supply. - Activation Timescale: Minutes to several hours. Flexibility for Voltage: - Need Description: Short term ability to keep the bus voltages within predefined limits, a local and regional requirement. - Main Rationale: Increased amount of distributed power generation in the distribution systems, resulting in bi-directional power flows and increased variance of operating scenarios. - Activation Timescale: Seconds to tens of minutes. Here, flexibility needs are considered from over-all system perspectives (stability, frequency and energy supply) and from more local perspectives (transfer capacities, voltage and power quality). With flexibility support considered for both operation and planning of the power system, it is required in a timescale from fractions of a second (e.g. stability and frequency support) to minutes and hours (e.g. thermal loadings and generation dispatch) to months and years (e.g. planning for seasonal adequacy and planning of new investments).ISGAN Disscussion paper