Optimal planning and operation for a grid-connected solar-wind-hydro energy system in wastewater treatment plants

This study proposes a multi -objective optimization model for a grid -connected wind-solar-hydro system in wastewater treatment plants, addressing trade-offs among electricity utilization cost, self-sufficiency, complementary effect, and carbon emission. Two modes are explored: one allowing energy export and another leading to curtailment. A case study from a plant with design scale of 50,000 m 3 /day in China found that a higher complementary rate can slightly increase costs, lower self-sufficiency, and increase carbon emissions. Compared to the initial scheme without the solar-wind-hydro system, the design modes of export and curtail reduce electricity costs by 2.15 and 0.87 million CNY, carbon emissions by 2760 and 1439 tons annually, and increase self-sufficiency to 52% and 42%, respectively. The levelized cost of energy is 25% higher and total installed capacity decreases by 54% when surplus cannot be exported. A 6.7% curtailment minimizes the electricity utilization cost. Complementarity rates show seasonal fluctuations, peaking in August, with the highest yearly rate of 0.1528 at a solar -to -wind capacity ratio of 1.747. Output ratios remain stable across different treatment scales under curtailment mode: imports about 60%, wind and solar about 20% each, and hydropower 2%. Price changes and potential for zero -carbon operation are further discussed.