This study presents a strategy to decrease the cost of purchasing electricity from the grid and the operation and installation costs of solar photovoltaic power plants (SPPPs) for twenty years by using self-organizing migration optimization (SOMA) and modified self-organizing migration optimization (MSOMA) to find the SPPPs’ capacity. The test system is investigated by installing SPPPs in two locations with the same load demand and the given solar radiation, where radiation in location second is higher than in location first. The results show that MSOMA is more stable than SOMA. Two methods find the optimal capacity of SPPPs for each location. However, the results demonstrate that SPPPs in a location second over are much higher than the first.