In this paper, we develop a preventive maintenance (PM) strategy for a solar photovoltaic system composed of solar panels functioning as a series system. The photovoltaic system is considered in a failed state whenever its efficiency drops below a predefined threshold or any electrical wiring element is damaged. In such a situation of failure, a minimal repair is performed. The proposed PM strategy suggests systematically replacing n panels with their respective wiring system every time units T over a finite operating time span H. The panels to be preventively replaced are selected by the maintenance agent after an on-site overall assessment of all panels, making sure every time not to replace panels previously replaced during a given replacement cycle of all panels of the system. An analytical model is proposed in order to simultaneously determine the optimal PM period, T, and the optimal number of solar panels, n, to be replaced at each PM. This is done by modeling and minimizing the expected total maintenance cost over the finite operating time horizon H. A numerical example is presented to illustrate the use of the proposed modelling approach and to discuss the obtained results. The latter provide the optimal solutions (T*, n*) for different combinations of input parameters. They also show the economic relevance of the proposed PM strategy through estimation of the economic gain when comparing the situations with and without preventive maintenance.

Wind turbine gearbox degradation driven by lubricating oil contamination represents one of the most environmentally and economically consequential challenges facing modern wind energy operations. This study proposes a dual-reservoir imperfect preventive maintenance strategy designed to extend gear train service life, reduce the carbon footprint of maintenance operations, and recover renewable energy production losses inherent to conventional intervention practices. The proposed architecture employs two alternating oil reservoirs. While one supplies the active lubrication circuit at full turbine output, the second undergoes filtration, completely decoupling the filtration operation from production continuity. When the concentration of metallic particles resulting from gear wear exceeds a predefined contamination threshold in the lubricating oil, imperfect preventive maintenance (IPM), performed in parallel with an oil change operation, is initiated; this action partially restores the gear train failure rate to an intermediate value between the degraded and as-new states. A mathematical model is derived to jointly optimize the filtration interval TF and the preventive maintenance interval TM, minimizing the average total cost per unit time over a finite operational horizon while explicitly incorporating environmental costs attributable to each filtration cycle. Numerical optimization yields the optimal filtration interval TF and preventive maintenance interval TM that minimize the total average cost per unit time over the operational horizon H. A dedicated environmental performance assessment demonstrates that the proposed strategy substantially recovers lost wind power generation, significantly reduces hazardous lubricating oil waste and lowers total CO₂-equivalent emissions. This confirms the strategy’s meaningful contribution to sustainable wind energy operations. Sensitivity analyses confirm the robustness of the optimal solution across varying operational and economic conditions, providing wind farm operators with an adaptable and environmentally responsible decision-making framework.

Actuellement, la compétition entre les entreprises se traduit par la révision des stratégies industrielles courantes dans le but d’améliorer simultanément les plans de production et de maintenance. En réalité, la non-satisfaction du client dans les délais est due souvent à des critères aléatoires liés essentiellement à la demande et aux défaillances soudaines des systèmes de production. Par conséquent, il est nécessaire de développer des politiques de maintenance intégrées à la production en tenant compte des contraintes liées au stockage, à la demande et au taux de défaillance. Dans ce travail, nous nous intéressons à une problématique industrielle qui s’articule autour du développement de différentes politiques de maintenance intégrées à la production. Le système considéré consiste en une machine fabriquant plusieurs types de produits, dans l’optique de satisfaire des demandes aléatoire avec des niveaux de service donnés. On note que l’originalité de notre étude, par rapport à l’existant en littérature dans le domaine de la maintenance intégrée à la production, consiste à considérer un système à multi-produits. Dans cette étude nous avons développé et optimisé analytiquement des politiques de production pour un système à multi-produits devant satisfaire plusieurs demandes aléatoires caractérisant respectivement différentes clients. Ces politiques consistent à établir des plans périodiques de production pour chaque produit, minimisant les coûts liés à la production et le stockage tout en satisfaisant un taux de service prédéfini pour chaque produit. Par la suite, en tenant compte de l’influence des plans économiques de production obtenus sur l’évolution de la dégradation du système de production, nous avons développé des stratégies optimales de maintenance. Plusieurs scénarios ont été étudiés selon les durées des sous-périodes de production et le coût de setup de chaque produit. En fin, des études de cas ont été traitées afin de confronter les résultats analytiques établis

This study investigates a commonly used maintenance strategy for wind turbine gearboxes in a wind farm located in southern Morocco. The gearbox condition is monitored through temperature sensors, and when a critical temperature threshold is reached, the turbine’s production rate is deliberately reduced to facilitate cooling. After a predefined cooling period, the turbine resumes its normal production rate. As these overheating-cooling cycles become more frequent over time, operators must decide when to replace the gearbox. The replacement involves either installing a new identical unit or refurbishing the existing one, with the timing of this decision relying solely on the judgment of the maintenance crew. In collaboration with this wind farm, we develop an analytical model and a solution procedure to optimize the gearbox renewal period. The model balances the costs associated with production losses during cooling phases and the financial and operational impacts of gearbox renewal. A critical constraint considered in the model is the minimum Full Capacity Operating Rate (FCOR) that must be maintained throughout the renewal cycle. The optimization model determines the ideal renewal period, T*, that minimizes the total cost per unit of time while ensuring compliance with the required FCOR. The model is extensively tested using various problem instances. An example is presented, and a sensitivity analysis is conducted to evaluate the influence of gearbox reliability and production loss costs on the optimal maintenance strategy. The results underscore the importance of model- and data-driven decision-making in optimizing maintenance operations and highlight the significant impact of reliability variations on maintenance planning.