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In the last decade, pit thermal energy storage (PTES) systems have been used as a large-scale heat storage solution in district heating systems due to their low specific investment cost and high storage efficiency. Despite the existing knowledge on thermal energy storage (TES) technologies, their economic and environmental impacts have not been quantified in the literature, and very few studies have studied PTES as part of the energy system. For this reason, the energy system model Balmorel was used to quantify the impact of TES on the energy system, particularly PTES, and compare it to the tank thermal energy storage (TTES) alternative. The investigation was focused on Denmark and its neighboring countries. It was found that it was only the energy systems using TES that could achieve carbon neutrality by 2050. The main reason was the added flexibility due to the energy storage that allowed the system to have a 35% higher PV capacity, 10% higher wind capacity, and lower levels of curtailment. Additionally, systems with TES had 2.4 €/MWh lower average heat price (with 24% lower peak price). When comparing PTES with TTES, it was found that PTES systems were more advantageous, achieving a 1.5 €/MWh lower average price of heat. • Integration of thermal energy storage in energy systems using the Balmorel model. • Sector coupling was included by modeling the power, heat, gas, and transport sectors. • Thermal storage enabled 10% lower average heat price and 24% lower peak price. • Thermal storage allowed high renewable utilization, limiting dispatchable production. • The impact of pit storages on the energy system was quantified and compared to tanks. [ABSTRACT FROM AUTHOR]