This chapter investigates the most cost-efficient energy storage solution for a net-zero office building in Trondheim, Norway. For each month from December 2021 to August 2024, we determined the optimal combination of latent thermal energy storage and electrical storage by solving a convex optimization problem aimed at finding the most cost-efficient energy storage solution. Our analysis indicates that a combination of electrical and thermal energy storage, specifically 67 kWh and 104 kWh respectively, represents the optimal solution for the whole period. We explored seasonal variations in optimal storage configurations, finding a greater demand for thermal energy storage during winter months. This is primarily driven by higher energy prices, higher energy price fluctuations, and increased thermal energy demand during winter. While electrical energy storage needs also increase in winter, this is mainly attributed to higher energy prices and energy price fluctuations. Ultimately, our findings highlight that high energy prices and significant energy price fluctuations are the primary drivers for implementing energy storage solutions.