In recent years, the technology of waveguide-based planar solar concentrators has been getting more attention in the Concentrated Photovoltaics (CPV) sector due to its compact design and performance versatility and its extended potential applicability from large power plants to built environments, such as Building Integrated Photovoltaics (BIPV). W. ••Review on waveguide-based Planar Light Concentrator (PLC) technology with reference of optics design and optical materials.••Covered material and systems design specifications for geometric, luminescent, and diffraction based PLC.••Summarized and tabulated different waveguide-based PLC technologies and its performance.••Discussed future prospects, practical impacts and challenges in the context of Building Integrated Photovoltaics.Planar waveguidePlanar light concentratorSolar concentratorGeometric opticsDiffraction opticsLuminescent solar concentratorsConcentrated photovoltaicsBuilding integrated photovoltaicsBeing the most abundant natural source of energy, solar energy is considered the future of the global renewable energy sector. However, unlike direct utilisation of solar energy (for example, daylighting applications), energy converted utilisation of solar energy is limited to the low energy density of input solar radiation for the required conversion, which can be either thermal or electrical. With the global urbanisation expansion, the area utilisation of these solar power conversion systems and their environmental impacts is also becoming a major concern [,, ]. The most straightforward approach that can be adopted to address this issue is concentrating solar radiation on a finite area using techniques of optical light concentration [,, ].Through the ages, the designs for solar light concentration evolved from imaging optics (mirrors and lenses) [6,8] to modern planar Fresnel optics [9,10]. However, the conventional optics systems suffer from bulkiness and cost-effectiveness due to the large optics elements and focal length of light concentration, which in turn increase the mounting cost. Later, planar optics-based lens and mirror systems were introduced, which reduced the system's volume and thereby offered a compact and slim design [9,11,12]. Reforming the designs further with multi-optical light concentrating elements largely reduced the system volume [,,, ]. However, the collection of energy fro. Waveguide-based PLC essentially consists of a planar (shape can be extended from flat plate to circular, etc., with regular or irregular cross-section) light guiding element, enabling light transport through reflection at surfaces through total internal reflection (TIR) or mirror reflection. The condition of light transport is determined by the primary optics, which enables the amount and nature (spectral selection) of light output, which is collected from the lateral face. The general schematic of waveguide-based PLC is shown in Fig. 1. Depending on the primary optics, they are classified as geometric optics-based PLC (which utilises reflective and refractive elements for light concentration and is coupled to the waveguide), LSC (which utilises luminescent molecules for light concentration with spectral selectivity), and diffraction optics based PLC (which use diffraction gratings for light redirection and spectral selection).The parameters defining the merit of waveguide-based PLC are:•1.Concentration ratio (or) geometric concentration (GC): This is a direct indication of the system's general design merit. It is the ratio of the inlet aperture of primary optics to the concentrated light area (output plane), or PV cell area.
