Optimization strategies of micro-hydropower systems to supply remote isolated communities

Resumen

Universal access to energy constitutes one of the biggest challenges that humanity has to face in the coming years. Modern societies are strongly dependent on electricity, which is required to run factories, processing plants, transport systems and health services, among many others. It plays such an important role in fulfilling the basic human needs that it has become a clear indicator of economic and social well-being. Although access to energy has kept increasing during the last decades, along with world population and industrialization, the highly unequal distribution in the patterns of energy use around the world are worrisome. Nowadays, more than one billion people still lacks access to electricity. These people are especially located in rural areas of developing countries and rely on traditional fuels or wood for the main household needs. This not only relegate living conditions at the low subsistence level, but also constitutes a big barrier to their social and economic development. In this context, social and political pressure to electrify deprived areas in developing countries has increased, growing consensus among international development partners. Several initiatives, such as the United Nation (UN) Millenium Development Goals (MDGs), have established the route and the objectives to target the universalization of energy access. The main difficulty in the expansion of electricity access to deprived areas lies in the dispersed and remote nature of the consumers. This cause that the costs of extending the electrical grid increase, which translates into a higher cost of the energy for the consumers. This not only discourages the interest of potential investors but also of the consumers, who generally find themselves in a context of low-income and limited resources. Small-scale decentralized schemes constitute an efficient solution, which is gaining relevance in the field. These schemes operate isolated from the grid, providing a wide capability of including Renewable Energy Sources (RES), due to the absence of constraints related to the grid. The combination of decentralized schemes with RES constitute a clear advantage to deal with the previously cited issues, with the additional benefit of sustainability. For these reasons, these projects remain in the spotlight of rural electrification initiatives in developing countries. Although RES systems have demonstrated to constitute an efficient strategy to deal with energy poverty, there are still some challenges that must be addressed in order to guarantee their best potential. This has motivated a deep study in the literature, and the development of optimization and design strategies of RES systems for rural electrification constitute a relevant line of research at the present. These works, which embrace a large range of areas of engineering, aim to improve the performance of these strategies regarding different aspects involved, such as efficiency, reliability or affordability. This thesis stems from an international cooperation project that pursuits the improvement of the design methodology of Micro-Hydro Power Plants (MHPP) for supplying remote, rural communities in deprived areas. MHPPs are small-scale hydraulic plants capable of supplying small communities with a high reliability and low investment and maintenance costs. These plants are based on transforming potential energy of the natural height difference of a water course into electrical energy. The characteristics of the plant are such that its performance is strongly conditioned by the precise emplacement of the different elements, constituting an interesting engineering problem which is generally not addressed on its most suitable way. This work proposes different formulations and approaches to optimize a MHPP for a certain emplacement. First, a general model of the MHPP is developed by means of the energy conservation of the water flow. The resulting equations are then used to formulate an optimization problem that pursuits the search of the most suitable layout of the MHPP. This is done in the form of a cost minimization, in such way that the overall cost of the plant is desirable to be as low as possible. To guarantee that the MHPP fulfills the required performance, a set of constraints related to the level of generated power and the amount of water flow used are introduced. In addition, the physical feasibility of the layout is imposed, for which the terrain height profile must be considered as an input. To validate the goodness of the formulated problem, it is transformed into an Integer Linear Programming (ILP) form and applied to an example problem, for which an arbitrary discretization of a river profile is introduced. Five different cases are proposed to evaluate the effects of the different parameters of the model, and it is solved by means of a Branch-and-Bound Algorithm (BBA), with which successful solutions are found. Secondly, once the optimization problem proposed has been validated, two different evolutionary approaches are developed to address a more complex version of the optimization problem, which results from considering the diameter of the penstock as an optimization variable. Two different Genetic Algorithms (GAs) are proposed. The first of them addressed the optimization problem in a discrete mode, on the same basis than the ILP formulation. This algorithm is applied to the example problem introduced previously, obtaining noticeable improvements with respect to the ILP approach. To verify the performance of the algorithm with a non-uniformly discretization, it is also applied to a real scenario problem, where a real set of data from a topographic survey is introduced as an input. Regarding the second GA, a shape preserving interpolation of the discretization points is applied to determine a continuous approximation of the river profile. This approach is applied to the real scenario introduced previously, and the improvements of the solutions demonstrate its goodness. Finally, the application of the methodology to a real electrification project in Honduras is presented. To this end, a pilot community is selected in West-Honduras, where an aerial topographic survey is developed. The application is summarized by means of three main improvements of the existent methodology: (i) optimizing the layout, (ii) improving the manufacturing of the turbine and (iii) installing a remote monitoring system. The successful results of this application demonstrate the capability of the proposed approaches to improve the traditional design methodologies and be replicated for future electrification projects.