## 1 Introduction  
Climate change is a major concern facing humanity due to the significantly negative impact of carbon emissions generated by conventional power sources in electric energy production. There is evidence of global support by many governments and organizations around the world to finance the implementation of renewable energy sources such as wind and solar power. Solar power is recognized as a friendly electric energy generation system with respect to the environment, as it has zero greenhouse carbon emissions and requires no fossil fuel consumption. Currently, PV technology is growing rapidly around the world due to increasing solar cell efficiency and decreasing prices. According to a report by the European Photovoltaic Industry Association (EPIA), the total PV capacity has been increasing exponentially, from 102.2 GW in 2012 to 138.9 GW in 2013 [1]. The output power of PV systems differs from the power generated by conventional sources due to the high uncertainty of PV power output, and the availability associated with PV system components [2; 3; 4] and their relative configurations. Electric power utilities and customers are therefore concerned about the reliability of PV-integrated power systems. Previous studies have discussed the system reliability of adding PV systems to electric power system grids using both analytical [5; 6] and simulation techniques [7; 8]. [PERSON] and [PERSON] [9; 10] discuss the adequacy benefit associated with installing renewable energy sources in electric power systems. A system well-being model is used in these works with combining deterministic and probabilistic technique to provide useful reliability indices for test system containing renewable energy. The reliability contribution of photovoltaic and wind energy sources is presented evaluated in these studies. Most reliability studies however consider PV systems as a whole component, and do not incorporate the sub-components and the design configurations of the PV topology in the evaluation. PV power systems are composed of components that are vulnerable to failures with different probabilities. The structure of power electronic converters in PV systems can be broadly classified into centralized-inverters, string-inverters, and micro-inverters. The structures of central and string PV systems often have similar electric components, but are differently configured in terms of connecting the solar array to the inverter. A central PV system topology is composed of multi-strings topologies that are connected to only one inverter. However, one inverter is connected to each string in a string PV system topology. Micro-inverter topology, on the other hand, requires one inverter per solar panel. Previous published works do not consider all the aforementioned topologies. The quantitative assessment of reliability for an entire PV system is essential in determining the overall reliability contribution of adding solar power to electric power systems, and this has not been sufficiently addressed in the available literature. This paper presents a comprehensive overview of the reliability models of PV systems, and presents the reliability quantification process of central, string, and micro-inverter PV systems. The developed models are embedded in the reliability evaluation methodology to obtain a discrete probability distribution in the form of a capacity outage probability table (COPT) [4] for each component group using individual component failure rates assuming exponential distribution of times to failure. The loss of load expectation (LOLE) [7] and the loss of energy expectation (LOEE) [7] indices are used in this paper to quantify the reliability of the PV-integrated systems. The capacity credit (CC) and the effective load carrying capability (ELCC) are calculated to estimate the capacity contribution by the different PV system topologies. The application of system reliability risk indices provides valuable quantitative risk measures, and is illustrated using a small isolated power system (SIPS).