Feasibility Study of a Combined Wind and Solar Park within the Energy Storage Lake of Delta21

Abstract

The penetration of the renewable energy sources in the global market has been constantly growing over the last years. This trend is expected to accelerate even more in the future due to the improving technologies, the economies of scale, the competitive supply chains and the improving developer experience. The main challenge for a faster and wider implementation of these resources is their intermittent character and the limitations that this implies. A concept that successfully deals with this variable energy output is the Hybrid Power Plant (HPP). HPPs combine at least two different sources of energy with the goal of delivering stable power with reduced fluctuations throughout the year. In addition, HPPs present various other synergies such as in operational costs or in the developing processes, that could lead to a reduced Levelized Cost of Energy (LCOE). The goal of this thesis is to assess the potential synergy of a combined wind and solar park for the case of the Energy Storage Lake (ESL) of the project Delta21. The Delta21 project has a twofold character: firstly, the usage of the ESL as a large battery integrated with green energy production and secondly the protection of the inland against floods due to high sea level or superfluous river discharge. The main challenge for this specific case is the large water level fluctuations within the lake in a daily basis due to the operation of the lake. The feasibility of a hybrid wind and solar park can be examined by various different perspectives and disciplines. Among these relevant components, the most frequently studied ones are the optimization of the energy resources, the use of common electrical infrastructure and the effect of the intermittent wind turbine shadows on the solar panels. Due to the special conditions, with the large water level fluctuations met at the lake, two more components become critical. These are the type of foundation of the wind turbines and the mooring configuration for the floating solar units. This project is evaluating a new potential synergy that regards the use of the wind turbine towers as anchor- ing points for the floating solar units. Therefore, the research is focused on the estimation of the forces acting on a floating solar unit. These forces are a combination of wind loads acting on the solar panels and the freeboard of the floaters, and wave forces acting on the submerged part of the floaters. In particular, the technology of the floating solar boat as introduced by GroenLeven and the small-scale wind turbines as designed by Dutch Wind are adopted for this project. Analytical formulations are used for the calculation of the wind loads. As for the wave forces, the linear potential theory is used and the calculations of the hydrodynamic coefficients and wave exciting forces are performed through the Boundary Element Method (BEM) software NEMOH. After the computation of first order wave forces and the corresponding responses of the floaters, the far-field approach is used for the estimation of the Quadratic Transfer Function (QTF) of the drift force. The methodology developed in this project and the accuracy of the model are validated with the use of reference data that regard the interaction of connected floating units placed in a close proximity and the corresponding second order wave forces as predicted by the far-field approach.