This paper applies the hippopotamus optimization algorithm (HOA) for optimizing the simultaneous integration of solar photovoltaic systems (PVSs), wind turbine systems (WTSs), and capacitor banks (CBs) in IEEE 25-node unbalanced and 69-node balanced distribution power grids. The harmonics caused by nonlinear loads and renewable power sources' converters are taken into account. The HOA is run for optimal solutions to a multi-objective problem with five specific objectives, including 1) investment, operation, and maintenance costs for grid-connected units, 2) annual energy purchasing cost, 3) active power losses, 4) voltage deviation, and 5) emissions. Finally, the investment, operation, and maintenance costs of PVSs, WTSs, and CBs are $6.956 million and $6.273 million for the two systems for a 20-year period. Compared to the base grids, the energy loss and the annual energy purchasing costs are reduced by 76.49% and 66.29% for the first grid and by 83.63% and 55.68% for the second grid. The optimal penetration level of the renewable energies is 64.83% and 52.34% for the two grids, respectively. The unbalanced voltage and harmonic distortion indexes satisfy the IEEE stdandards 45–2002 and 519. Thus, this study demonstrates significant benefits to distribution power grids through the optimal installation of PVSs, WTSs, and CBs.