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Desalination using solar stills is an ancient economic method for water desalination. Over the years, research and development in the area of solar still has resulted in increased distillate yield by means of integration of PCM (phase change material), photo-voltaic thermal (PVT), etc with the still. Nano-PCM is an upcoming technology which modifies the thermal performance of PCM. The aim of this research is to analyze the efficiency of 20 solar stills including nano-PCM based solar stills considering various input and output criteria using integrated fuzzy analytical hierarchy process (AHP) and data envelopment analysis (DEA). The efficiency derived here is relative with regard to the parameters and stills considered in this study. The result infers that, even though the productivity of stepped solar still with sun tracking system was high, but when techno-economic aspects were considered it is not among the top solar stills. The analysis indicated pyramid type solar still, single slope solar still with PVT, solar still with NPCM (paraffin + copper oxide), solar still with NPCM (paraffin + titanium dioxide) and solar still with PCM (paraffin) occupies the top five positions with relative efficiency of 100, 100, 88.47, 88.46 and 76.93% respectively.

The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. An annual performance analysis of the Solar STIG cycle is presented for sites in Israel and India, with moderate and high annual direct insolation. The cycle operation was simulated in two modes: constant power output and variable power output following the variation of solar input. The solar contribution to the electricity production of the hybrid cycle and the solar to electricity efficiency were calculated, where the conventional reference system was either a conventional STIG or a conventional recuperated Brayton cycle. Results show annual solar fraction of up to 31% in constant power mode and up to 33% in variable power mode. The annual solar to electricity efficiency was in the range of 22–26% when the reference efficiency was based on the recuperated Brayton cycle, and 12–16% when the reference efficiency was based on an optimal conventional STIG cycle. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at only 200 °C.

A critical analysis on wind farms has been carried out to improve the performance and reliability of wind energy system. The effect of its improvement has been studied with the Optimal Renewable Energy Mathematical (OREM) model which is developed for sustainable generation in India. The performance and reliability of the wind turbine generators have been evaluated in a demonstration windfarm (6 MW) in India. The windfarm is situated in Kayathar, a village in the south of Tamil Nadu State. The average technical availability, real availability and capacity factor have been analysed from 1991 to 1995 and they are found to be 92%, 54% and 19% respectively. Fault analysis for grid failures has been done using pareto analysis. The analysis indicates that when grid drop failures are reduced by 50%, the overall reduction in the frequency of faults would be 35.2%, which is significant. The reliability analysis has also been done for the wind turbine generator. The failure rate is high to an extent of 6.7×10−5 h−1 in the case of a yaw control defect and the factor of reliability is found to be 0.5 at 10 000 h. The OREM model developed reveals that when the reliability factor of wind energy system is improved from 0.5 to 0.9 then the utilisation of wind energy would be increased by 82%.