Economic impact of renewable energies in marginalist electrical systems: methodological approach for sustainable investment planning

This study develops a public-planning-oriented cost–benefit framework for marginal-cost-based electricity systems. It compares counterfactual with- and without-project scenarios using a hydrothermal economic-dispatch model and distinguishes gross price-related consumer-payment effects from contract-related and investment costs. The methodology is applied to the Peruvian interconnected electricity system using the Cerro del Águila hydropower project as an empirical benchmark for scale and economic information. The additional 400 MW are represented by a modelled portfolio comprising ten 20 MW photovoltaic plants and ten 20 MW wind plants, incorporated as forced renewable generation using a common 21.5% capacity-factor assumption. The deterministic base-case simulation indicates that this additional capacity reduces the demand-weighted average marginal cost by US$6.27/MWh. Applying this differential to the annual electricity-demand input produces a model-based present value of gross price-related consumer-payment effects of approximately US$3.18 billion over 30 years at a 12% discount rate. The present value of the positive contract-price differential is approximately US$176.62 million. In the principal benchmark investment-inclusive evaluation, which also deducts the reported initial investment cost of US$948 million, the estimated net benefit remains positive at approximately US$2.06 billion. These results are conditional on the dispatch assumptions, the forced-generation configuration, the fixed-demand treatment, tariff pass-through, and the defined public-planner and consumer perspective. The findings indicate that renewable integration may reduce the generation component of consumer payments when marginal-cost reductions are transmitted through the applicable tariff-setting mechanisms. The proposed framework provides a structured decision-support procedure that can be adapted using context-specific technological, market, contractual, and regulatory parameters.