In this pioneering work, we propose a manufacturing plan for a 3D hollow hemispherical solar selective absorber (HSSA). The HSSA stands out as a superior choice compared to planar absorbers, thanks to its numerous benefits and wide-ranging applications, particularly in solar harvesting and photothermal desalination. Importantly, HSSAs reduce radiative losses by emitting thermal radiation along their curved surfaces, which enhances concentration ratios and minimizes these losses. This study addresses the intricacies of fabricating the HSSA's 3D convex shape. Our approach draws inspiration from a set of 2D flat solar selective absorbers (SSAs), each fine-tuned to adapt angles and intensities in response to solar radiation. These optimized SSAs are then arranged within a grid shell framework. As an illustrative example, we consider the widely-used selective coating W/Al2O3-W/Al2O3. We optimize parameters, including layer thicknesses and the incorporation of metal in the absorber, to attain optimal values for photothermal conversion output under varying oblique incidence angles. For this optimization process, we employ the non-parametric particle swarm algorithm known as 'phasor,' recognized for its autonomous search for global optima in complex and multimodal optimization problems. Our calculations yield a remarkable photovoltaic conversion efficiency, reaching up to 0.966429. This research is driven by the aspiration to maintain such high efficiency, even in the face of fluctuations in solar radiation incidence and intensity throughout the day. Simplifying calculations, we divide the hemisphere into five spots, optimizing each for peak performance according to its positioning. These collective efforts and innovations culminate in the development of a compact solar water desalination system, engineered for efficient operation, even in the presence of one sun.