Visibly transparent solar harvesting surfaces are an exciting new approach to harvesting solar energy around buildings and mobile electronics to improve their efficiency and autonomy without impacting their appearance. The recent demonstration of ultraviolet (UV) and near-infrared (NIR) selective light harvesters have enabled transparent luminescent solar concentrators (LSCs) that boast unparalleled scalability, flexibility, aesthetic quality, and affordability. Consequently, the question of the efficiency limits has emerged in these new systems. In this perspective, the theoretical efficiency limits of these concentrator systems are reviewed and practical considerations are outlined to approach these limits. For UV and UV/NIR selective harvesting single-junction transparent LSCs are constrained thermodynamically to 21%, which increases to over 35% in fully transparent multipanel devices with light trapping. In deriving these limits, key material and engineering challenges are identified to fully optimize transparent solar concentrators that can push them towards commercial reality.