The aim of this paper is to investigate the effect of component reliability towards the system reliability of the Uninterruptible Power Supply (UPS) systems. New methodologies are applied to the AC Uninterruptible Power Supply (AC UPS) topologies to evaluate system's reliability by estimating the system's Failure Rates and Mean Time Between Failures. Reliability parameters obtained from five major AC UPS configurations were compared and discussed in detail. Equations for calculating the MTBF is presented along with component reliability estimates. Sensitivity analysis on the major components of the AC UPS was performed to investigate the effect on the overall system reliability.

Precise evaluation of risk and reliability is crucial for decision making and predicting the outcome of investment in a photovoltaic power system (PVPS) due to its intermittent source. This paper explores different methodologies for risk evaluation and reliability assessment, which can be categorized into qualitative, quantitative, and hybrid qualitative and quantitative (HQQ) approaches. Qualitative methods include failure mode analysis, graphical analysis, and hazard analysis, while quantitative methods include analytical methods, stochastic methods, Bayes’ theorem, reliability optimization, multi-criteria analysis, and data utilization. HQQ methodology combines table-based and visual analysis methods. Currently, reliability assessment techniques such as mean time between failures (MTBF), system average interruption frequency index (SAIFI), and system average interruption duration index (SAIDI) are commonly used to predict PVPS performance. However, alternative methods such as economical metrics like the levelized cost of energy (LCOE) and net present value (NPV) can also be used. Therefore, a risk and reliability approach should be applied together to improve the accuracy of predicting significant aspects in the photovoltaic industry.