Posters

Abstract

For an accurate and reliable energy yield assessment, attention needs to be invested in all major steps of the calculation process, including the losses.   Much attention has concentrated on wake losses, and indeed this is often the largest loss category, however other important loss categories also deserve attention: Electrical Availability is often an important contributor to the energy yield losses, in particular for offshore windfarms.   In brief, the key loss categories are: * Wakes (a.k.a. inter-turbine effects) * Windturbine performance * Windturbine availability * BoP (Balance of Plant, e.g. primarily electrical transmission) availability; the focus of this presentation * Electrical efficiency   The typical approaches to estimating the Electrical Availability Loss are as follows: * Default values, e.g. 97-99%, potentially depending on the transmission concept * Bottom-up calculations, based on industry recommendations for the key components, i.e. CIGRÉ (Conseil International des Grands Réseaux Électriques) However limited effort has been invested in validating and confirming these methods.  This presentation contributes to rectifying that deficiency.   The approach is to validate methods against Reported Performance for: * OFTOs (Offshore Transmission Operator) in the UK * TenneT TSO (Transmission System Operator) in Germany   Due to the configuration of the available validation datasets, the BoP is defined as follows: * Offshore (windfarm) substations * Export cables, both offshore and onshore * Onshore (windfarm’s grid connection) substation   The following are excluded from this definition: * Windturbine transformers, which are typically included in the windturbine availability * the inter array cables connecting the windturbines to the offshore substation; however this loss is typically negligible, with exceptions of where serial design or installation faults have occurred * the national electrical grid’s onshore grid connection substation, since this would typically be included within a “grid connection availability” category.   Electrical Availability is modelled by focusing on the major components of the transmission system, specifically: * Substation transformers * Transmission cables   The rationale being that: * these major components contribute the overwhelming majority of the anticipated losses * information about the configuration and specification of the minor components is usually not available   By comparing modelled against reported availability, it has been found that: * Substation availability is broadly as anticipated, however with important exceptions * Export cable availability appears to outperform industry assumptions, i.e. there are far fewer outages than expected   Finally data on the reliability of the grid connections is available at the UK OFTOs, thus allowing recommendations for the Grid (Connection) Availability category to be developed.  It is seen that availability depends on the type of system being connected to, i.e. Transmission vs. Distribution.   In addition to confirming the Losses, it is possible to develop recommendations for the associated Uncertainty, by examining the standard deviations across the performance of the individual transmission systems within the datasets.   In conclusions, assessing the loss estimation methods against actual performance provides confidence in those methods, as well as allowing lower losses to be confidently applied for the majority of offshore windfarms.