Hybrid Energy Storage Systems for Renewable Integration: Combining Batteries, Supercapacitors, and Flywheels

—Renewable-energy integration into power grids is constrained by the variable output of solar and wind resources. This paper proposes a Hybrid Energy Storage System (HESS) that couples lithium-ion batteries, supercapacitors, and flywheels and governs them with a Unified Mathematical Method (UMM) combining moving-average filtering with threshold-based cut-off logic. The architecture is modelled in HOMER Pro for the Grand Forks, ND (USA) resource profile and bench-marked against “Grid+Renewables†and “Grid+Renewables+Battery†baselines. The full three-storage configuration supplies 1 032 320 kWh yr−1 of useful energy—an increase of 77 % over the no- storage case—and eliminates 1.36 Mt CO2 yr−1 of emissions, a 245 % improvement relative to renewables alone. Valued at the Social Cost of Carbon (US$51 t−1) and the 45Q tax credit (US$85 t−1), the avoided emissions translate to annual economic benefits of US$69 000–US$116 000. The UMM reduces false cut-off events by more than 30 %, prolonging component life and enhancing overall system reliability. These results confirm that a tri-technology HESS managed by a unified control layer delivers superior technical performance, environmental gains, and financial returns compared with single-storage or no-storage configurations.