Ensuring food security while reducing reliance on grid electricity and freshwater is critical for sustainable agriculture, particularly in arid regions where conventional greenhouse systems face high water-energy demands that conflict with Sustainable Development Goal 7 (Affordable and Clean Energy). This study developed and field-tested a novel greenhouse vegetable production system (PGRH) that integrates photovoltaic power generation, greenhouse rainwater collection, and low-pressure irrigation to enable off-grid, water-efficient vegetable production. The system performance was evaluated through field trials in Northwest China, complemented by a national-scale Water-Energy-Food (WEF) nexus assessment using optimization modeling under varying climatic and structural scenarios. The PGRH system demonstrated significant capabilities, reducing water consumption by 9.34% and electricity consumption by 90.69%, while net income increased by 9.10%. The WEF nexus modeling revealed that the system performance is highly dependent on regional climate, identifying region-specific configurations that maximize water savings, energy self-sufficiency, and economic return. Optimization analysis demonstrated that in arid northern regions, a smaller greenhouse with large rainwater storage is optimal, whereas in rainy southern regions, larger greenhouse structures with less storage are preferable. Validation with melon further confirmed the model's transferability. In conclusion, this study provides a comprehensive framework for decoupling greenhouse food production from external energy and water resources. The findings offer actionable, data-driven recommendations for policymakers to promote sustainable agriculture tailored to local climatic conditions.