Design of a module for a 10 MJ toroidal YBCO SMES for the mitigation of PV plants intermittency

The progressively increasing penetration of electricity from solar photovoltaic plants, needed for a successful deployment of renewable energy sources, strongly depends on the economic cost of system integration, that should also mitigate the intermittency of PV electricity. Among the different available energy storage systems that could be applied to compensate the fluctuating PV power, Superconductive Magnetic Energy Storage (SMES) are attractive because of their high deliverable power and efficiency, and their virtually infinite number of charge-discharge cycles without degradation. Here we present the design of a module for a 10 MW toroidal YBCO SMES, with a charge/discharge time of 1 s, including the superconducting coil, the power feeding system and the cryogenic cooling. The design has been performed with a functional analysis approach, translating the system-level requirements into detailed functional and performance requirements for the sub-components, imposing a maximum value for the module radius (0.5 m) and a maximum magnetic self-field of 4 T. The ampere-turn design is based on a stack of 7 commercial 12 mm-width 2G YBCO tapes, with a nominal current of 330 A at 77 K, so that conservatively a total effective current of 1kA at 50 K can be retained for the stack. For the winding pack of a single module, the optimized design points to a multi-layer coil with radius ~ 0.45 m, wound using 52 layers in parallel, each with 26 turns, with a total inductance of ~2 H and a maximum self-field below 4 T. Nine modules are needed for the entire SMES. Such design is checked by a detailed 2D axisymmetric electro-magnetic model, purposely developed in COMSOL Multiphysics®. The conceptual design of the power control system is also presented, together with that of the cryostat, focusing on the thermal insulation and the cryocooler.