• Energy Research
• 2016-2025close

AbstractOvershot water wheels are hydropower converters generally employed for head differences up to 6 m and maximum flow rates of 150−200 L/s per meter width. The maximum hydraulic efficiency (8...

Abstract Nowadays, due to the need for clean energy and sustainable electricity production, hydropower plays a central role in satisfying the energy demand. Particularly, use of low head micro hydropower plants is spreading worldwide, due to their low payback periods and good environmental sustainability. Gravity water wheels are micro hydropower converters typically used in sites with heads less than 6 m and discharges of a few cubic meters per second. Although water wheels were scientifically investigated as far back as the eighteenth century, they were largely ignored throughout the twentieth century, and only in the last two decades has there been a renewed interest in their use among the scientific community. In this paper a review on gravity water wheels is presented, distinguishing between undershot, breastshot and overshot water wheels. Water wheels technology is discussed focusing on geometric and hydraulic design; data and engineering equations found in historic books of the nineteenth century are also presented. Water wheels' performance is described examining experimental results, and modern theoretical models for efficiency estimation are presented. Finally, results achieved through experiments and numerical simulations were discussed with the aim of optimizing the performance of gravity water wheels. The results showed that maximum efficiency of overshot and undershot water wheels was around 85%, while that of breastshot water wheels ranged from 75% to 80%, depending on inflow configuration. Maximum efficiency of modern water wheels can be maintained at such high values over a wider range of flow rates and hydraulic conditions with respect to older installations. Hence well designed water wheels can be considered as efficient and cost-effective micro hydropower converters.

Lubricant oil is used in hydropower units to minimize friction, improving the turbine efficiency and reducing the wear. However, oil production is a pollutant process, while eventual spills may affect water quality and damage freshwater ecosystems. In this study, the lubricant oil consumption of the European hydropower fleet was estimated (considering its installed capacity of 254 GW). The energy required to extract and process the oil was also estimated based on available literature data. The oil consumption was estimated to be 22 × 103 tons/year, and the associated CO2 emissions are 105 tons/year. The lubricant oil costs EUR 116 million per year. Although this is only 0.0022% of the oil consumed as a primary energy source in the European context, and less than 0.4% of the European industry consumption of lubricant oil, results show that new bearing types and oil-free turbines (e.g., self-lubricating or water-lubricated turbines) can improve the sustainability of the hydropower sector, minimizing the risks and impacts associated with incidental oil spills and leakages. The provided data can also be used for Life Cycle Assessment analyses.

ABSTRACTWater wheels can be efficient hydropower converters at low heads and low discharges. The paper presents the results of a study of a breastshot water wheel in a laboratory experimental channel. The obtained data show that breastshot water wheels can reach a maximum efficiency of about 75%, at a rotational velocity which is about 60% of the runaway velocity. The maximum efficiency is constant over a wide range of flow rates. A dimensional analysis is then carried out and a simple relationship for estimating the maximum mechanical power output of geometrically similar wheels is determined, relating the Newton number (dimensionless maximum power output) to the Reynolds number (function of the hydraulic conditions and channel geometry).

L'utilisation croissante des sources d'énergie éolienne et solaire pour réduire les émissions de CO2 dans le secteur électrique entraîne une disparité croissante entre l'offre et la demande d'électricité. Par conséquent, il y a un intérêt accru pour des solutions de stockage d'énergie abordables pour résoudre ce problème. Le stockage hydroélectrique par pompage (PHS) apparaît comme une option prometteuse, capable de fournir un stockage d'énergie à court et à long terme à un coût raisonnable, tout en offrant l'avantage du stockage d'eau douce. Pour identifier les emplacements potentiels des PHS au Brésil, les réservoirs hydroélectriques existants étant les réservoirs inférieurs, nous avons utilisé une méthodologie innovante qui combine (i) un modèle d'implantation d'usine qui exploite des données topographiques et hydrologiques à haute résolution pour identifier les sites les plus prometteurs pour des études ultérieures. (ii) Une méthodologie économique a été appliquée pour configurer les projets PSH identifiés par le modèle d'implantation d'usine en termes de capacité installée et de temps de décharge, et pour sélectionner les projets les plus attrayants. (iii) Une analyse complète des impacts socio-environnementaux des projets a été réalisée, ce qui permet d'éliminer les projets ayant des impacts graves. Les résultats ont créé un classement de 5600 projets mutuellement exclusifs par valeur actuelle nette (VAN). La VAN la plus élevée est de 2 145 USD, ce qui fait référence à une usine PHS dans le bassin de Doce et le barrage de Salto Grande en tant que réservoir inférieur. Le réservoir supérieur stocke 0,36 km3 d'eau et un barrage de 75 m de haut, le PHS dispose d'un tunnel de 2 km, d'une capacité de puissance de 1 GW et d'un débit de décharge de 220 h. L'article montre un vaste potentiel pour les PHS hebdomadaires, mensuels et saisonniers avec des réservoirs inférieurs existants au Brésil. La creciente utilización de fuentes de energía eólica y solar para reducir las emisiones de CO2 en el sector eléctrico está causando una creciente disparidad entre la oferta y la demanda de electricidad. En consecuencia, existe un mayor interés en soluciones asequibles de almacenamiento de energía para abordar este problema. El almacenamiento hidroeléctrico por bombeo (PHS) surge como una opción prometedora, capaz de proporcionar almacenamiento de energía tanto a corto como a largo plazo a un costo razonable, al tiempo que ofrece la ventaja del almacenamiento de agua dulce. Para identificar las posibles ubicaciones de PHS en los embalses hidroeléctricos existentes en Brasil como los embalses inferiores, empleamos una metodología innovadora que combina (i) un modelo de ubicación de plantas que aprovecha los datos topográficos e hidrológicos de alta resolución para identificar los sitios más prometedores para estudios adicionales. (ii) Se aplicó una metodología económica para configurar los proyectos de PSH identificados por el modelo de ubicación de plantas en términos de su capacidad instalada y tiempo de descarga, y para seleccionar los proyectos más atractivos. (iii) Se realizó un análisis exhaustivo de los impactos socioambientales de los proyectos, lo que permite la eliminación de proyectos con impactos severos. Los resultados crearon una clasificación de 5600 proyectos mutuamente excluyentes por valor actual neto (van). El VPN más alto es de 2145 USD, que se refiere a una planta de PHS en la cuenca del Doce y la presa de Salto Grande como el embalse inferior. El embalse superior almacena 0,36 km3 de agua y una presa de 75 m de altura, el PHS tiene un túnel de 2 km, una capacidad de potencia de 1 GW y una tasa de descarga de 220 h. El documento muestra un gran potencial para el PHS semanal, mensual y estacional con los embalses más bajos existentes en Brasil. The increasing utilization of wind and solar power sources to lower CO2 emissions in the electric sector is causing a growing disparity between electricity supply and demand. Consequently, there is a heightened interest in affordable energy storage solutions to address this issue. Pumped Hydropower Storage (PHS) emerges as a promising option, capable of providing both short and long-term energy storage at a reasonable cost, while also offering the advantage of freshwater storage. To identify potential PHS locations in Brazil existing hydroelectric reservoirs as the lower reservoirs, we employed an innovative methodology that combines (i) plant-siting model that leverages high-resolution topographical and hydrological data to identify the most promising sites for further studies. (ii) An economic methodology was applied to configure PSH projects identified by the plant-siting model in terms of their installed capacity and discharge time, and to select the most attractive projects. (iii) A comprehensive analysis of the socio-environmental impacts of the projects was carried out, which enables the elimination of projects with severe impacts. Results created a ranking of 5600 mutually exclusive projects by net present value (NPV). The highest NPV is 2145 USD which refers to a PHS plant in the Doce Basin and Salto Grande dam as the lower reservoir. The upper reservoir stores 0.36 km3 of water and a 75 m high dam, the PHS has a 2 km tunnel, a 1 GW power capacity and discharge rate of 220 h. The paper shows a vast potential for weekly, monthly, and seasonal PHS with existing lower reservoirs in Brazil. يتسبب الاستخدام المتزايد لمصادر طاقة الرياح والطاقة الشمسية لخفض انبعاثات ثاني أكسيد الكربون في قطاع الكهرباء في تفاوت متزايد بين العرض والطلب على الكهرباء. وبالتالي، هناك اهتمام متزايد بحلول تخزين الطاقة بأسعار معقولة لمعالجة هذه المشكلة. يبرز تخزين الطاقة الكهرومائية التي يتم ضخها كخيار واعد، وقادر على توفير تخزين الطاقة على المدى القصير والطويل بتكلفة معقولة، مع توفير ميزة تخزين المياه العذبة. لتحديد مواقع الصحة والسلامة المهنية المحتملة في البرازيل، الخزانات الكهرومائية الموجودة هي الخزانات المنخفضة، استخدمنا منهجية مبتكرة تجمع بين (1) نموذج تحديد موقع المصنع الذي يستفيد من البيانات الطبوغرافية والهيدرولوجية عالية الدقة لتحديد أكثر المواقع الواعدة لمزيد من الدراسات. (2) تم تطبيق منهجية اقتصادية لتكوين مشاريع الصحة والسلامة المهنية التي حددها نموذج تحديد موقع المصنع من حيث السعة المثبتة ووقت التفريغ، واختيار المشاريع الأكثر جاذبية. (3) تم إجراء تحليل شامل للآثار الاجتماعية والبيئية للمشاريع، مما يتيح القضاء على المشاريع ذات الآثار الشديدة. خلقت النتائج تصنيفًا لـ 5600 مشروع يستبعد بعضها بعضًا حسب صافي القيمة الحالية (NPV). أعلى صافي قيمة صافية هو 2145 دولارًا أمريكيًا والذي يشير إلى مصنع خدمات الصحة العامة في حوض دوس وسد سالتو غراندي باعتباره الخزان السفلي. يخزن الخزان العلوي 0.36 كم3 من المياه وسدًا يبلغ ارتفاعه 75 مترًا، ويحتوي قسم الصحة العامة على نفق بطول 2 كم وسعة طاقة 1 جيجاوات ومعدل تفريغ يبلغ 220 ساعة. تُظهر الورقة إمكانات هائلة لخدمات الصحة العامة الأسبوعية والشهرية والموسمية مع الخزانات المنخفضة الحالية في البرازيل.

The Very Low Head turbine (VLHT) is an axial flow turbine developed for heads below 4.5 m and flow rates up to 30 m3/s. In this work, the state of the art, the technological advancements and the scientific gaps were discussed and generalized, with a special focus on design, ecological behavior, costs, performance at different flows, heads and rotational speeds. The flow field and the hydraulic behavior under different configurations (e.g. in presence of cavitation and with an upstream obstacle) were described, with the aim of deriving engineering suggestions. Results of ecological tests were generalized (fish survival rate is more than 90%) by using the blade strike model, proposing an expeditious method for a preliminary appraisal of the ecological impact on downstream migrating fish. Despite the hundreds of installations worldwide, especially in existing barriers, some scientific gaps need to be better addressed yet, e.g., the influence of the number of blades and axis inclination on the efficiency, the influence of flow, head and rotational speed on the flow field and a quantification of the head losses through the trash rack above the runner.

In the hydropower sector, the weight of electro-mechanical equipment is an important input data. During the design stage, it allows to estimate material cost, to perform Life Cycle Assessments and to consider adequate load factors on the supporting structures. At the end of the lifetime, in case of dismantling or retrofitting, the estimation of the equipment weight allows to appraise the material value and to plan the operational activities. However, the engineering knowledge is quite fragmented and limited on this topic, and only a few weight equations are available in the literature. In this contribution, the available equations are firstly reviewed and discussed. Secondly, data were collected both from the literature and from hydropower companies, and generalized to provide expeditious equations. The equations presented in this paper allow for a preliminary estimate of the weight of: 1) the runner of Pelton, Kaplan, Bulb, Cross-Flow (Banki type) and Francis turbines, and water wheels; 2) the casing of Pelton and reaction turbines; 3) draft tubes; 4) electric generators. Data on Vortex, Turgo and Hydrokinetic turbines, Archimedes screws and guide vanes are presented. The opportunities associated to innovative and lighter construction materials are discussed.