As the share of solar and wind in the energy mix increases, the inherent intermittency of these energy sources pose a great challenge for the Dutch power grid. The occurrence of problems with congestion and balancing power supply and demand are becoming more common. Companies in the Netherlands show potential to implement means for smart use of energy to alleviate these kind of problems. However, the gap between academic solutions and the industry is often too large. This research presents a method to find the optimal design of an integrated energy system in the Netherlands. A use case at Picnic is used to apply the proposed method. A flexible load scheduling optimisation algorithm is presented to explore the financial benefit of an integrated energy system that combines a photovoltaic system, an energy storage system, a cold storage system and a fleet of electric vehicles. The financial performance of different system designs are compared. Results show that the optimised load schedules for the EV fleet and CS system achieve a 2.6% decrease of energy costs with respect to the benchmark of Picnic. A PV system turns out to be beneficial for every size that the grid connection allows. This research finds 600 square meters to be optimal in the case of Picnic. An energy storage system would make optimised load schedules obsolete due to its flexibility. An energy storage system with a capacity of 250 kWh is found to be optimal according to the performance analysis. However, significant limitations in the assumptions of the storage system advise against installing it. Further research is required to elaborate the different elements in the proposed model. Different markets are suggested to use as a basis for load scheduling and a broader set of system designs is suggested to analyse their performance.