Distributed generation (DG) has gained prominence in distribution systems in recent decades due to its capability to reduce carbon footprint, improve power quality, voltage support and maintain a sustainable system. Although DG has numerous benefits, unplanned DG integration can adversely impact the power system parameters and the distribution company’s (Discom) income. This work addresses optimal site and sizing planning for renewable and dispatchable DG, considering long-term economic and technical benefits. A multi-objective (MO) problem is formulated to reduce the cost associated with DG units, their operation and maintenance (OM), fuel, emission, and operational objectives. The impacts of hourly variation in the power generation of renewable DG units and load demand profiles are investigated through case studies. Annual load growth and load modeling are included in the study to have a pragmatic model. An improved particle swarm optimization (IPSO) technique having chaotically varying inertia weight is used to determine the optimal solution. Profit and payback period (PP) calculations for the purchase and sale of electricity on the contract price for the project duration are discussed in detail. The proposed approach has been demonstrated to be effective through simulation studies conducted on the modified IEEE-33 bus and the real Italian distribution system.