Intermittency of renewable energy systems remains one of the major impediments to their adoption. Therefore, large-scale energy storage is essential for developing flexible, reliable electricity grids and integrating renewables within them. This work presents a comparative study of mechanical energy storage systems based on their working principle, factors that affect their performance, applications, advantages, and disadvantages. Pumped hydro, gravity-based, and buoyancy-based methods store energy in the form of gravitational potential energy. Flywheels store excess electrical energy in the form of kinetic energy via a rotating mass. Metal-organic frameworks and carbon nanotubes store potential energy in their structure under compressive or tensile forces. Springs can be used to momentarily store kinetic energy in pendulum energy harvesters. The application for these systems varies depending on factors such as energy density, power density, discharge time, and energy generation method. Some mechanical energy storage systems are well suited for utility scale. Others, like carbon nanotubes and metal-organic frameworks, are more suited to nano-scale applications. Finally, energy storage in springs can improve the performance of pendulum energy harvesters. Thus, mechanical energy storage has the potential to deliver value across different stages of the energy value chain.