Renewable energy resources are becoming more and more important for the electricity production regarding the security problem of nuclear energy and the limit of fossil fuels. Among the renewable resources, solar power is an interesting candidate for buildings that are the biggest consumers of the electrical grid. Indeed, integrating photovoltaic power systems on the roof of commercial and office buildings is permitting to reduce significantly their electricity consumption from conventional local grid. This paper presents a sizing method of photovoltaic panels for maximizing the match between the building's load profile and the solar energy generation shape without battery in taking into account the investment profitability. A cooling load management strategy is also proposed thanks to optimization based on the thermal inertia of walls for improving the self-consumption of the building. These methods are applied for a university building in north of Vietnam, in which we show the feasibility of on-grid PV system investment with respect to cost scenarios.