Value of flexibility in systems with large wind penetration
Résumé
The focus of this thesis is the quantification of the value of operation flexibility in systems with large penetration of wind generation. This begins with the quantification of the impact of wind generation (WG) uncertainty on the system's needs for frequency regulation and reserve. This is done by combing the stochastic behaviour of wind generation, demand uncertainty and generation outages. Two different approaches are compared to access the implications of using normal distribution approximations or direct representations of different sources of uncertainty. This is followed by an investigation of the relative impact of different sources of uncertainty on the reserve levels. For large wind penetration, wind becomes the dominant source of uncertainty driving most of the need for reserve. Procuring such large requirements increases the need for flexibility and the overall system operations cost. To mitigate these additional costs and improve system flexibility, the study explores the use of a combination of spinning and standing reserve to meet the increased reserve requirements. This combination minimises the cost of reserve and increases system flexibility. These benefits are more pronounced if a more accurate representation of uncertainty is used. Following this, a detailed analysis of the value of generation flexibility is performed. The analysis is based on the modification of traditional scheduling models to include WG and to take into account the relevant features of system operation flexibility. The value of flexibility is quantified for different conventional generation mix, different response and reserve technology compositions and generation technology flexibility, across a wide range of wind penetration levels. The key drivers for the value of flexibility are shown to be the increased response and reserve requirements (especially reserve requirements), the conventional generation mix and the inherent flexibility of must-run generation. This is driven mostly by the system's need for curtailing wind to maintain the generation/demand balance. To obtain a significant reduction of carbon emissions, however, a combination of must-run generation with a large penetration of wind is required. This results in a high economic and environmental value being placed on must-run generation flexibility. The high economic and environmental value attributed to flexibility is seen as an opportunity to explore alternative sources of flexibility, such as storage and demand side flexibility (DSF). To this end, this work also investigates the role that such enabling technologies can play in enhancing system flexibility, by contributing to standing reserve and load-levelling. To this end a new system operation tool is developed. This tool simulates system operation for forecasted and realised wind generation to optimise reserve scheduling and utilisation. This is required to quantify the value of value of using storage and DSF to provide reserve. This tool is used to quantify the economic and environmental value of these technologies for different conventional generation mix and wind penetration. The studies show that both technologies have economic and environmental benefits and this is more pronounced for low flexible conventional generation mix and higher wind penetration. The value is driven mostly from increasing the system's ability of using WG. This highlights the role that storage and DSF can play in enabling low carbon systems composed by a combination of low flexible conventional generation with a large wind penetration. Finally, the thesis also examines the role of storage and DSM to support network operation, particularly in systems like the UK where the connection of WG capacity is limited by network constraints. The use of these technologies, to increase network flexibility in situations of congestion, is explored through the development and application of a multi-period optimal power flow with storage and DSM included as part of the optimisation constraints. The study concludes that both technologies present benefits and have a complementary role. Its value is maximised under different conditions and depends on the cost of generation and location of demand, across the network.