• Energy Research

Making a decision usually means selecting one from different alternatives to solve a problem according to a set of criteria. Multicriteria analysis usually offers a quantitative approach to ease decision-making by ranking the alternatives. However, uncertainty can arise when rating the importance of criteria and the adequacy of each alternative for each criterion, due to two factors: first, answers are usually expressed in linguistic terms that do not have a unique quantification; and second, there might be a lack of confidence in the response. Most multicriteria procedures combine fuzzy numbers and linguistic scales to deal with the first factor, but underestimate confidence issues. In this context, this work develops a Methodology for Integrated Multicriteria Decision-making with Uncertainty (MIMDU), which considers both factors of uncertainty. MIMDU is structured in three phases: (1) a novel procedure based on fuzzy rating scales to model uncertain opinions; (2) a fuzzy formulation of the compromised ranking method to rank the alternatives; and (3) a systematic procedure for results’ interpretation comparing a crisp ranking (without uncertainty) and a fuzzy-based ranking (with uncertainty). The methodology is illustrated with a generic example case, aiming to prove its potential application in any sector. Results show that MIMDU helps decision-makers to choose the most reliable alternative, since significant differences in ranking with and without uncertainty can be addressed. A sensitivity analysis is carried out to bare the effect of confidence in the alternatives evaluation, concluding that worse rankings are obtained for alternatives that are less confidently evaluated. A final comparison with the standard fuzzy VIKOR method shows MIMDU’s major preciseness in modelling non-confident opinions and providing more useful and complimentary information to better assist decision-making. Peer Reviewed

Grid-connected photovoltaic (PV) facilities are more attractive than ever due to the electricity price surges and the reduction of solar energy generation costs. This paper develops a solving procedure including a simulation model to analyze the techno-economic performance of PV-battery facilities, taking into account the latest Spanish regulatory framework. The procedure finds the best facilities for multiple objectives, maximum profitability and maximum self-sufficiency, in different locations, load profiles and economic scenarios. The results indicate that PV modules are profitable without subsidies, with installations between 1 and 6 kWp. Meanwhile, batteries are only convenient when seeking maximum independence from the grid, with capacities up to 9 kWh. The findings suggest that the economic feasibility of facilities is influenced by the location and compensation rate surplus electricity, while the facility is mainly determined by the load profile. A sensitivity analysis shows that a variation in grid tariffs and technology prices has a limited impact on the facility's size but modifies the system's profitability. Finally, an analysis of the latest unprecedented grid price surges indicates that self-consumption facilities help become a more resilient society against unexpected events. Therefore, policymakers should keep promoting the adoption of these technologies and keep the current advantageous regulations. Peer Reviewed

Assembly line balancing problems (ALBPs) arise when designing or modifying an assembly or production line and usually consist in assigning the tasks to the workstations along the line in order to meet some given objectives. Traditionally, it is assumed that there is exactly one workpiece in each workstation and that the workstation has access to the entire workpiece. In practice, this assumption may be sometimes too restrictive. An example is the case of the automated assembly of printed circuit boards. In this type of lines the length of the workpiece might be larger than the width of the workstation. Therefore, each workstation can only access to the limited portion of the workpieces that fall inside its accessibility window. In this work we present an extension of the ALBP to the case of workstations with accessibility windows (AWALBP). The problem is described and a simple-to-implement solving procedure is proposed, which consists of i) an algorithm to obtain a good initial solution and ii) a simulated annealing algorithm for improving the obtained solution. Finally, a computational experience that validates the proposed procedure is reported. Peer Reviewed

Systems relying on renewable energies demonstrated to be a reliable and sustainable option to electrify isolated communities autonomously. Hybrid systems that combine different energy resources and distribution microgrids are the most efficient design configurations. The design of these systems requires the use of decision support tools, while projects' promoters generally dispose of low design resources. This study presents a heuristic method to design off-grid electrification projects based on wind and solar energies considering micro-scale resource variations and a combination of independent generation points and microgrids. The method considers generation far from users and a pre-selection process is presented in order to screen the initial pool of potentially infinite generation points. Different algorithm versions are evaluated and performances are compared with existing tools: VIPOR, known software for microgrids design, and a recently developed mixed integer linear programming (MILP) model. The proposed heuristic performs better than VIPOR with mean improvements of around 6% and, for communities of more than 40 users, considerably enhances solutions obtained by the MILP model with a much lower computational time (1 min against 1 h). The method is a complete and simple tool that can efficiently support the design of stand-alone community electrification projects with renewable energies. (C) 2014 Elsevier Ltd. All rights reserved.

Electrification systems based on the use of renewable energy sources are suitable for providing electricity to isolated communities autonomously. Specifically, electrification by wind power is one of the technological options that have been used recently in projects implemented in the Andean highlands of Peru. To date, these projects have tended to install individual microwind turbines at each demand point. Alternatively, we propose a solution that considers both individual generators and microgrids.We develop a mathematical model that gives the location and size or type of the wind turbines and the design of the microgrids, taking into account the demand of the consumption points and the wind potential. The criterion is the minimization of the initial investment cost required to meet the demand. The model is validated by application to a real case in the northern highlands of Peru. Results show that microgrids are used despite the village dispersion, and the solutions significantly reduce the initial investment costs. Peer Reviewed

In industry there are production systems consisting of more than one assembly line. If these are close together, it is possible for an operator to perform tasks from two adjacent lines assigned to his station (this will be a "multi-line station")

Wind-photovoltaic systems are a suitable option to provide electricity to isolated communities autonomously. To design these systems, there are recent mathematical models that solve the location and type of each of the electrification components and the design of the possible distribution microgrids. When the amount of demand points to electrify increases, solving the mathematical model requires a computational time that becomes infeasible in practice. To speed up the solving process, three heuristic methods based on mixed integer linear programming (MILP) are presented in this paper: Relax and Fix heuristics, heuristics based on a Corridor Method and Increasing Radius heuristics. In all algorithms first a relaxed MILP is solved to obtain a base solution and then it is used as a starting point to find a feasible solution by searching in a reduced search space. For each type of heuristic several options to relax and to reduce the solution space are developed and tested. Extensive computational experiments based on real projects are carried out and results show that the best heuristic vary according to the size of instances.