Thermodynamic and Exergy-Based Evaluation of Machining and Minimum Quantity Lubrication (MQL) Effects on Robotics Solar-Battery Systems for Green Hydrogen Mini-Grids in Nigeria

Green hydrogen mini-grids can improve electricity access and reduce diesel dependence in Nigeria, but their sustainability depends on both the operational thermodynamic performance of the PV–battery–electrolyzer chain and the embodied burdens of locally manufactured enabling hardware. This study presents an integrated thermodynamic and exergy-based framework that couples operational exergy analysis of a PV 200 k–battery 800 kWh–electrolyzer 80 kW mini-grid with manufacturing-stage cumulative exergy consumption (CExC) accounting for machining-intensive robotics PV cleaning/inspection and PV mounting components under dry machining, flood cooling, and minimum quantity lubrication (MQL). Operational exergy balances based on solar radiation exergy quantify component exergy destruction and irreversibility shares, while the manufacturing model combines machining electricity, lubricant-related exergy, tool-life-based tooling allocation, and rework/scrap penalties to compute part-level and kit-level embodied exergy indicators. At a representative high-irradiance design hour (), solar exergy input is 881.4 kW and the largest exergy destruction occurs in PV conversion (701.4 kW), with additional downstream irreversibilities in electrolysis (28.0 kW), power electronics (7.0 kW), and battery charging (3.0 kW). Manufacturing results for representative aluminium and steel components show that MQL yields the lowest CExC compared with dry and flood regimes due to reduced machining energy, improved tool life, and reduced rework/scrap rates, demonstrating a measurable pathway for lowering embodied exergy of robotics-and-mounting hardware. The combined results indicate that integrating second-law operational analysis with manufacturing-stage exergy accounting strengthens lifecycle sustainability assessment and provides actionable design levers for robotics-enabled green hydrogen mini-grids in Nigeria.