In a micro-generation system that includes renewable energies, the reliability assessment might consider the random behavior of the renewable resources. When a planning of this kind of generation systems are carried out, the objectives of interest must be optimized based on outcome of each one, since join them in a single function is not always possible or recommend. In this paper a multi-objective optimization of a generation system is done, using as objectives the cost of energy, two different reliability indexes and the percentage of renewable energy used. The power generation system combines solar and wind energies, diesel generators as conventional source and the possibility to take energy from the grid. Each energy source and the load was modeled as a multi-state system (two or more performing levels), in order to represent in a closest form their variable nature. This multi-state representation of the generators and loads combined with the Universal Generating Function enables the estimation of the reliability indexes of the system, reducing the computation time, while maintaining adequate results. The proposed system was compared with Monte Carlo Simulation in the reliability assessment objective to evaluate the performance of the Universal Generating Function in this case. Finally the proposed system gives us as a result a variety of utilities that can serve as a basis for further evaluation in the whole planning process and it allows us to observe the changes produced on the solutions planning due to the impact of the renewable energies on reliability.