Abstract
The ever-growing diffusion of renewables as electrical generation sources is forcing the electrical power system to face new and challenging regulation problems to preserve grid stability. Among these, the primary control reserve is reckoned to be one of the most important issues, since the introduction of generators based on renewable energies and interconnected through static converters, if relieved from the primary reserve contribution, reduces both the system inertia and the available power reserve in case of network events involving frequency perturbations. In this scenario, renewable plants such as hydroelectric run-of-river generators could be required to provide the primary control reserve ancillary service. In this paper, the integration between a multi-unit run-of-river power plant and a lithium-ion based battery storage system is investigated, suitably accounting for the ancillary service characteristics as required by present grid codes. The storage system is studied in terms of maximum economic profitability, taking into account its operating constraints. Dynamic simulations are carried out within the DIgSILENT PowerFactory 2016 software environment in order to analyse the plant response in case of network frequency contingencies, comparing the pure hydroelectric plant with the hybrid one, in which the primary reserve is partially or completely supplied by the storage system. Results confirm that the battery storage system response to frequency perturbations is clearly faster and more accurate during the transient phase compared to a traditional plant, since time delays due to hydraulic and mechanical regulations are overpassed. A case study, based on data from an existing hydropower plant and referring to the Italian context in terms of operational constraints and ancillary service remuneration, is presented.
Highlights
The European electrical grid has been experiencing deep changes in recent years
Considering the evolution of the electrical power system, in which traditional generating units tend to be replaced by renewables with consequent reduction of the available reserve power, this paper discusses the possible extension of the frequency regulation ancillary service to run-of-river hydroelectric plants
Even including the installation costs, in any case decreasing in recent years, the Battery Energy Storage System (BESS) integration shows high Internal Rate of Return (IRR) since it allows the traditional plant to operate at higher power, closer to the hydraulic availability
Summary
The European electrical grid has been experiencing deep changes in recent years. In particular, the exploitation of Renewable Energy Sources (RESs) for electricity generation is dramatically modifying the traditional paradigm. The PCR ancillary service is supposed to be extended by the standards to include run-of-river hydroelectric plants In this way, only considering the countries reported, an increase of about 45 GW in the overall installed rated power of plants supplying PCR is expected in the European area (data are evaluated as in [11] and generally refer to 2015). Grid codes do not consider the opportunity of supplying PCR by means of BESSs. In this paper, the authors propose equipping an existing hydroelectric run-of-river power plant with a battery storage unit, assuming as a working hypothesis that the standards might require the PCR ancillary service to this type of power generator. Power saturation is considered as an upward reserve minimum requirement
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