Rising electricity demand increases reliance on carbon-intensive sources, harming the environment. Solar energy offers a cleaner alternative, but choosing between a solar parking system and a diesel generator is complex due to differences in operation, investment, and revenue potential. Studies comparing these under multiple economic scenarios and CO2 emissions are limited. This study presents an integrated economic and environmental comparison of a grid-connected solar parking system versus a diesel generator for Qom University of Technology. The solar system was designed for the existing parking layout, using Meteonorm data, PVsyst simulations, and PV*SOL for emissions. Diesel output and fuel use were based on its operating schedule. Both were evaluated under four economic scenarios varying service life, replacements, and revenues. Annual output was 120.35 MWh (solar) and 21.12 MWh (diesel). Scenario 4; including electricity sales and lighting revenue; yielded the best economics. Over 20 years, future value was $63,273.88 (solar) versus $50,261.42 (diesel). Solar generated ~$2,328 annual revenue, with levelized energy costs of $0.0243/kWh versus $0.094/kWh for diesel. Though solar required higher upfront investment, it became more attractive when electricity could be sold. Environmentally, diesel emitted 13,531 kg CO2/year, while solar avoided ~56,564 kg/year. Overall, the best choice depends on conditions, but under monetization scenarios, solar offers substantial long-term economic and environmental benefits.