Efficient Grid Interconnection Act of 2021 This bill establishes requirements concerning (1) the equitable allocation of costs for electric grid upgrades; and (2) the deployment of grid enhancing technology or equipment that increases the capacity, efficiency, or reliability of a transmission facility or transmission system. Specifically, it directs the Federal Energy Regulatory Commission (FERC) to issue regulations that require public electric utilities to allocate the cost of upgrades to the electric grid, such as upgrades to interconnect renewable generation projects, among all customers that benefit from the upgrades. In determining which parties benefit, FERC must consider all material benefits of the network upgrade, including environmental benefits and those that cannot be directly quantified. In addition, FERC must issue regulations that apply to regional transmission organizations, independent system operators, or transmission planning coordinators when they are processing requests to interconnect generation projects or energy storage projects to the electric grid. The regulations must require such organizations, operators, and coordinators to study deploying technology or equipment that increases the capacity, efficiency, or reliability of a transmission facility or transmission system.