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In power system load flow studies, it is common to ignore wind park (WP) losses completely, since WPs are obliged to provide reactive power as a free-of-charge ancillary service. Strongly simplified WP loss estimations are also widespread. Prevailing loss modelling approaches may result in substantial and so far usually ignored reactive power allocation inefficiencies. The innovation of this paper lies in demonstrating this and in presenting an alternative modelling approach that combines speed, ease-of-use and accuracy. Calculations are based on a generic WP connected to 110 kV. It is simulated once using gearless permanent magnet synchronous generators and once using doubly fed induction generators. In this way, for the first time, the consequences of neglecting differences between wind generator types when calculating reactive power-related losses are systematically quantified. Loss-minimal dispatch is assessed using heuristic optimal power flow. Relevance of findings is demonstrated for the application of reducing system losses based on reactive power control of WPs in closed-loop optimal power flow schemes. It is shown that non-consideration of WP losses may lead to dispatch decisions where the increase in WP losses outweighs the achieved loss reduction in the 110 kV system by 400%. The study facilitates comparing reactive power ancillary services from WPs to that of other technologies from an economic perspective. It concludes by a benchmarking overview of pros and cons of modelling alternatives

Transition toward high shares of power production from wind and photovoltaics (PV) brings about a substantial increase in controllable reactive power (Q). The capability to provide Q independent of active power production (24/7) is available at comparably low or even zero investment cost. Yet, this capability is not required by network connection codes and only rarely utilized, even if available. In a first step, we take an overall economic perspective and review the economic competition of 24/7 Q provision from variable renewable power plants (VRPP) with alternative Q resources. Technical restrictions to be respected are discussed, as well as the reliability requirements related to investment-planning relevant Q provision. Competitiveness is significantly influenced by Q utilization rate and connecting voltage level. For practical implementation of 24/7 Q procurement from VRPP, its value needs to be assessed. We review possible approaches from overall economic perspective. We conclude that in operational decisions, VRPP Q should be valued at marginal cost, whereas in Q investment planning decisions, full cost should be considered. We derive the pros and cons of making 24/7 Q provision a mandatory part of network connection codes. For system operators (SOs) to integrate available capacity, regulatory acknowledgment of related revenue impact should be considered. We present possible solutions. Summarizing, the contribution presents the status quo in research on cross-voltage level, investment-relevant Q provision by VRPP. Using the presented methodology for value assessment, areas for further research are systematically pointed out. competitive, DSO, investment planning, procurement, reactive power, TSO | INTRODUCTIONThe reactive power (Q) procurement problem of system operators (SOs) consists of making available sufficient over-and underexcited Q resources at suitable locations in the electrical power system. We investigate this problem for systems with high share of variable renewable power plants (VRPP) based on wind and photovoltaics (PV). We focus on quasistationary Q provision in onshore systems. Reactive power injected at a specific node of a system influences local voltage. Taking a crossvoltage level approach, this also applies to the interfaces of different voltage levels. For example, the residual of Q from an medium voltage (MV) system will influence the voltage of the high voltage (HV) node it is connected to. Reactive power