Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Review of the methods for evaluation of renewable energy sources penetration and ramping used in the Scenario Outlook and Adequacy Forecast 2015. Case study for Poland Mateusz Andrychowicz, Blazej Olek ⁎ , Jakub Przybylski Lodz University of Technology, 90-924 Lodz, Poland ARTICLE INFO Keywords: RES ramping RES penetration Power system flexibility ABSTRACT On 30th of June 2015 the European Network of Transmission System Operators for electricity (ENTSO-e) published the ENTSO-e Scenario Outlook & Adequacy Forecast (SOAF) report providing information about impact of Renewable Energy Sources (RES) on power system and potential lack of flexibility in power systems of thirty seven European countries. The flexibility is measured using Residual Load (RL) which equals actual demand decreased by solar, wind and must-run generation, and which is covered by dispatchable power units (generally thermal and hydro). According to the report, the RL for Europe is strongly irregular and unpredictable among member states. As a consequence, high generation ramping is forecasted which leads to necessity of high system flexibility. The results are presented as a distribution of the RES penetration including must-run and distribution of the hourly RES ramps. However, the methodology used by ENTSO-e is questionable. This paper aims to review methods of the RES penetration and the RES ramp assessment presented in the SOAF report. The evaluation is performed on the grounds of the authors’ critical approach and in a form of comparison of the displayed techniques with the hitherto carried out studies in this field worldwide. Furthermore, information which is crucial for the stakeholders in the power industry is identified and selected. Finally, based on the collected knowledge, the authors present new, augmented method subject to various already developed techniques, as well as the innovative and creative contribution. 1. Introduction 1.1. Impact of developing RES on power systems stability European climate and energy policy foster development of Renewable Energy Sources (RES) in the European Union. The increase in the RES share in total energy consumption is also observed in Poland [1]. Development of the RES driven by the European Energy and Climate policies is an opportunity to reduce CO 2 emissions from power industry. Nevertheless, despite numerous merits, increasing role of the renewables in the power system have also disadvantages. The most serious issue is their unpredictable and dynamically changing generation profile. Thus, operational management of the power system with high share of photovoltaics (PV) and wind generation (WG) is a challenging task for Transmission System Operators (TSO). Typically, in electricity markets, generating units are ranked in a merit order, i.e. in an ascending order of variable costs, together with the volume of the power offered to be generated. Such market structure makes RES the privileged units in power injection into the grid. The reason for that are their nearly zero marginal costs [2–4]. Additionally, legal regulations guarantee energy purchase from RES producers regardless of demand. As a result, under some circumstances (e.g. sunny and windy Sunday), generation exceeds demand, which leads to unplanned energy exports through cross border connections and switching off thermal power plants. This case is called overgeneration or energy surplus [5]. As a consequence, the conventional power plants operate in an intermittent cycle which shortens their time of operation, reduces efficiency, reduces income and rises total costs [6]. The role of the conventional power plants is shifting from base load operation to fluctuating back-up of power [7]. Relevance of the abovementioned problems has been noticed by the pan-European authorities. On June 2015 the European Network of Transmission System Operators for Electricity (ENTSO-e) published Scenario Outlook & Adequacy Forecast 2015 (SOAF 2015), in which for the first was included analysis of the RES impact on the power systems in Europe [8]. The study focuses on assessment of the RES penetration and the RES generation ramps http://dx.doi.org/10.1016/j.rser.2017.02.069 Received 23 January 2016; Received in revised form 21 November 2016; Accepted 21 February 2017 ⁎ Corresponding author. E-mail address: blazej.olek@p.lodz.pl (B. Olek). Renewable and Sustainable Energy Reviews 74 (2017) 703–714 1364-0321/ © 2017 Elsevier Ltd. All rights reserved. MARK