The integration of Variable Renewable Energy Sources (VRES) creates challenges for meeting load demand. The lack of on-demand power generation of these VRES effectively threatens energy security. Therefore, storage facilities, especially hydrogen, have been broadly researched for potential implementation in our energy system, enabling on-demand power "generation". This thesis adds to this research by providing a framework on how VRES and long-term storage technologies can be most optimally utilized to ensure weekly or monthly energy security. This framework is explicitly applied to the Netherlands and reviews the opportunities of a VRES dominated future energy system. The framework consists of a VRES generation model and load model and identifies the optimal load coverage using single- and multi-objective genetic algorithms. The VRES generation model is designed for a weekly and monthly timeframe by using 31 years of available weather data (1988-2018), specifically average wind speeds and solar irradiance, for a number of locations in the Netherlands. Using the available weather data, power generation per MW of onshore wind, offshore wind, and solar PV are calculated. Subsequently, this calculated VRES power generation is compared to available real-world VRES power generation data and a correction factor is determined. Applying the correction factor to the more extensive weather data set allows to effectively create a VRES power generation model, based on the weather circumstances as in these 31 years. Additionally, a weekly and monthly 31-year load profile is determined, using available data for load demand in the Netherlands. Thereafter, both a single and multi-objective algorithm is tasked to provide load coverage in two main scenarios at minimum cost. First, load coverage is achieved exclusively utilizing VRES capacity. Secondly, a variety of long-term storage facilities are introduced in combination with VRES capacity to acquire energy security. Furthermore, these two methods for achieving energy security are restricted in a number of sub-scenarios, which represent the societal preference restrictions regarding VRES installations. Generally, energy security is most cost-effectively achieved utilizing long-term hydrogen storage facilities, as compared to an exclusive VRES approach. Specifically, alkaline electrolysis and hydrogen combined cycle gas turbines seem to be the most promising technologies to be applied for the hydrogen storage facility electrolysis and reconversion sub-steps respectively. Furthermore, societal preference has a significant effect on the total costs, increasing it considerably when offshore wind capacity is forcefully introduced in the VRES capacity mixture. Lastly, the timeframe considered for achieving energy security, either weekly or monthly, has a substantial effect on the total cost. The smaller weekly timeframe results in additional costs, as the long-term hydrogen storage facility, is utilized more broadly to meet load demand, increasing the capacity requirements for charging, discharging, and storage. Overall costs range between 139 and 211 billion Euros to achieve energy security using the more cost-effective long-term hydrogen storage approach, depending on the timeframe and societal constraints applied.