Solar energy utilization, at three fundamental steps viz. capture, conversion, and storage, has been stepped up within the last decade with about 1.6 % of world energy need. It is being projected that the future demand for energy will be more than double by 2050 and triple by 2100. However, there is a huge gap in the potential of solar energy availability (120000 TW of radiations) and its utilization (13 TW). Solar energy is being used broadly in three areas viz. solar electricity, solar fuel and solar thermal utilization. Available radiations, distributed along the infrared to the ultraviolet frequency spectrum, are captured using photovoltaic (PV) of inorganic, organic and hybrid technology, solar concentrators and conversion using the electrical, chemical and thermal route and storage using specialized materials.
In the last five years, rapid advances in the nanoscience and nanotechnology have allowed material structure manipulation at the nano-scale level. Notable are the fabrication techniques, such as lithography and self-assembly. This has been greatly accelerated with the advancements in the experimental techniques that allow probing at the very small length and time scales. Another force that enabled rapid progress in solar energy utilization is the advancements in biology. Control of natural assembly process of photosynthetic systems and self-repair and tolerance features adopted from nature extend the artificial solar thermal conversion system and water-splitting mechanism. Thus the advancements in structural biology allowed the deconstruction of natural solar energy converter to a reconstruction of artificial variants to maximize the targeted objective.
Biomass has been the source of energy since the beginning of human existence. Biomass-to-liquid fuel conversion efficiency, however, is very low i.e. about 1%. Current practice is to use biomass for secondary energy production from it to the liquid fuel. However, bio-inspired approaches to photochemical conversion have been proposed to intervene in the biomass to liquid fuel production path with the increase in conversion efficiency. Photo-driven catalysis mechanisms for CO2 reduction and H2O oxidation have also been proposed.
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Solar thermal is categorically utilized in low-temperature and high-temperature solar thermal systems. High-temperature applications used advanced solar concentration technologies such as line-focus system, central receiver systems, and solar tracking systems. Solar thermal to electric energy is obtained using thermoelectric and thermophotovoltaic (TPV) power generators using advanced materials having a figure of merit >3 ZT. Recently, the optical systems have been advanced to a stage where concentration ratio up to 5000 suns (1 sun= 1 kW/m2) having a capability to split water into H2 and O2 in the water-splitting thermochemical cycle using metal oxide redox reaction, are possible.
Although much progress has been made at the capture, conversion and storage level in solar energy utilization, there are challenges — technological developments that induce mass production possible are needed; new, high temperature sustainable and highly efficient nano-engineered materials are required; the cost of the solar energy utilization has to be brought down by large margin.
