Off-Grid energy systems are growing in popularity as an independent source of energy to satisfy electricity needs of individual households or smaller communities, mainly in developing countries where the main grid is either not developed or the grid is uneconomical to extend due to remoteness of the location. The Isle of Eigg in Scotland has been successfully using a hybrid off-grid system for several years to provide a reliable 24-h electricity supply to the islanders. This ex-post analysis of the Isle of Eigg system investigates its performance and explores possible alternative configurations which could work more effectively and efficiently. Simulations were carried out using HOMER software for the existing system and for alternative configurations of energy generation. It is found that the existing overcapacity has been instrumental in ensuring a reliable supply but continued reliance on diesel generators adds to the cost. More wind power capacity addition can reduce reliance on fossil fuels and modular sizing of generators instead of adding large capacities could have reduced the idle capacity. This experience suggests that providing reliable off-grid electricity supply is possible but is costly without suitable capital subsidies. Appropriate system design suited to the local condition is important for developing a viable system.