The threat of the changing climate conditions has pushed the world's interest in the renewable energy systems. Solar energy is considered as an ideal renewable energy since it is considered as more cleaner and sustainable sources of energy. However, higher capital cost of installation of 'off - grid solar photovoltaic (PV) system and lack of perception of system reliability are the major drawbacks of the solar systems which can also have a negative effect on the manufacturer's reputation and in some cases, on the technology. Hence the reliability estimation of the solar PV system becomes extremely important. The aim of this research paper is to design and estimate the reliability of an off grid solar PV system. The greatest challenge for the PV system reliability estimation is the changing input to the system which is solar radiation. This research study designs a solar PV system for a house located South east Queensland (Australia) and later estimates the reliability of this designed system. The study used both mathematical and software tools while designing and reliability estimation of the off grid solar PV system. The result of this research can be used to model any other Off grid solar PV system's reliability and availability with some modifications based on climatic factors.