Detailed Analyses of Meteorological Time Series for the Sizing of Storages in Renewable Energy Systems - Uncertainties Related to Inter-Annual Variabilities
Abstract
When designing solar power based clean energy supply systems in all scales – from autonomous devices to solar home systems, village power supply and nation-wide systems - the intended degrees of autonomy and supply security are key figures. Due to the variability of the meteorological conditions on all time scales there is – besides the technical reliability of the systems - an intrinsic uncertainty whether the the intended degrees can be reached over the live time of the systems. The identification of a reasonable system sizing – for the case of PV, load and battery systems, selection of a combination of installed PV and storage capacity - is usually done by use of time step simulations based on an at minimum annual data sets (Lund 2018) of the meteorological conditions. The selection of these sets – especially their length has been recognized as a critical issue (see e.g. Heide et al 2010, Pfenninger and Staffell 2016, Bryce et. 2018, Rinaldini 2021, and, for the case of projected future data sets Jerez et.al 2015). In this context there is a broad discussion on the year-to-year variability of the annual irradiance sum and thus the expected annual PV generation. In contrast, the interannual variability of challenges for the storage systems connected to occurrence of extended periods of low generation due to overcast situations has received less attention. As discussed in e.g. Beyer 2020, investigating the possible contribution of PV generation to add to the isolated power supply system for the Faroe Islands, the in annual irradiance sum provides information usable for storage sizing only if the required capacity is the order of magnitude of months of load. For systems with storage sized to cover weeks or days of load the storage is challenged by low irradiance periods with length of weeks or days respectively, whose occurrences is not strongly coupled to the annual conditions.