Simulation Assisted Implementation of Radiative Cooling Materials to Grid-eMotion Flash Charging Units

Hitachi Energy produces the fastest flash-charging system in the world (Grid-eMotion Flash) as well as a large-scale electric vehicle charging system (Grid-eMotion Fleet) for public and commercial transport. The Energy Transfer System Control Box, which is installed on the roof of any electric bus (e-bus) that may be connected to these chargers, represents a key component in controlling the charging process. Passive cooling methods are preferred for dissipating the heat generated in the electronics of such devices. Today, the enclosure of these components is made of an aluminum alloy, which is normally coated with grey paint. Materials-based radiative cooling represents a cooling technology with great potential, particularly for components typically located in outdoor environments. In this paper the process of selection and testing of alternative surface coatings is presented. Five coatings have been selected for study: regular grey paint, radiative cooling film, radiative cooling paint and two formulations of solar reflecting paints. Numerical simulation models, complementing data acquisition from real-world experiments, were developed which allow the performance of the different coatings to be evaluated over a range of environmental conditions. Several levels of solar irradiation and temperature. For all coatings, the predictions output from the simulation model were found to agree with measurement data, with a model accuracy of ±3 K. The results of both simulations and experiments indicate that a temperature reduction inside the device of up to 8 K relative to standard grey paint coating may be achieved.