Abstract Hybrid energy systems (HES) combine two or more energy conversion devices for meeting a common energy end use. Isolated hybrid systems are utilized for electrification of remote locations where the extension of grid becomes infeasible due to techno-economic constraints. There are numerous options for energy integration in hybrid systems, as there can be combinations of renewable and conventional generators. A typical example is an integrated diesel generator–photovoltaic–battery system. Diesel generators, photovoltaic modules, and wind turbine driven generators coupled with energy storage in the form of batteries are usually employed in isolated hybrid systems. Series, switched, and parallel modes are the commonly adopted system configurations in hybrid systems. The appropriate design of HESs is essential for its efficient and reliable operation. There have been several approaches to solve the problem of system design. Methodologies range from simple calculation-based procedures to application of detailed mathematical models. For the design and analysis of hybrid systems, an appropriate mathematical model provides a logical equivalent specified by the system characteristics. Design-space methodology offers a set of tools for the identification of the set of all feasible system configurations capable of meeting the given demand conforming to specified levels of reliability. Design-space approach has been illustrated for an integrated diesel generator–photovoltaic–battery bank system.