Sodium-ion battery (NIB) technology has drawn increased attention for stationary storage applications owing to its potential in facilitating the transition to a world powered by renewables, mainly due to sodium's vast elemental abundance, lower costs, and suitable redox potential. Nevertheless, it is still a challenge to realize practical NIBs due to the lack of low-cost and high-performance electrode materials with sufficient power densities, cycling stability, and long life. This work examines the potential of sustainable hard carbons synthesized from the thermal transformation of readily available macadamia nutshell biomass to achieve NIBs with high specific and areal capacities. A comprehensive characterization of the hard carbons is performed to understand their structural and morphological attributes. The carbons synthesized at 1100 degrees C demonstrated excellent long-term cycling performance and specific capacities as high as 220 mAh/g at a current density of 10 mA/g. Furthermore, the areal capacity of 0.85 mAh/cm(2) was obtained at 20 mA/g, even at low mass loadings of 4.5 mg/cm(2). Based on these findings, the hard carbons prepared in this work are likely to be a promising candidate for the negative electrode in practical Na-ion batteries for grid-level energy storage.