Sustainability challenges of hydropower and its implication on Ethiopia’s economy

Ethiopia has the potential to be 100% renewable. Its renewables are capable to solve its energy poverty and energy shortage in East Africa. The country’s climate resilient green economy strategy considers energy as key enabler for vibrant economy. The objective of this paper is to identify key challenges of the energy sector by studying 12 years of electricity generation data, 2012 to 2023, and to analyze the sector’s performance with a special emphasis on hydropower. In this study, both quantitative and qualitative methods were employed to draw performances indicators. The quantitative results showed that the country achieved 30% of its energy development plan with a deteriorating performance from 94% to 40%. This performance works for hydropower too, which dominants the electricity development and supply. The declining performance comes from government’s monopoly in the sector, financial deficit due to ongoing internal crises and technical unavailability of power plants. This performance has greatly influenced expansion of industries, access to electricity, unemployment, and other economic activities. The authors advise the government, stakeholders, and development partners to consider the recommendations given in this paper to boost the energy sector development and keep the country in healthy economic pace by all measures

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.publishedVersio

Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load

The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.publishedVersio

Skred i magasin - overtopping av fyllingsdam fra skredgenererte bølger i magasin

Målet med FOU-prosjektet har vært å få mer kunnskap om bølgeoppskylling fra skred i magasin for fyllingsdammer, deriblant å utvikle en konkret metode for å beregne hvilke konsekvenser en overskylling har på fyllingsdammers sikkerhet. Fysiske modellforsøk på vassdragslaboratoriet ved NTNU ble sammenlignet med resultater fra numeriske simuleringer utført av NGI. Prosjektet viste bl.a. at NGIs numeriske bølgemodeller kan benyttes for beregning av overtopping av fyllingsdamme

Upgrading hydropower plants to pump storage plants: a hydraulic scale model of the tunnel system

Among the energy storage options, pump storage plants historically and currently exceed both in stored energy volumes and in power capacity. However, considering the high costs of developing new large pump storage projects and the environmental and social aspects, an environmentally and socially preferable solution is to redesign existing hydropower plants and upgrade them to pump storage plants. This paper presents a hydraulic scale model designed for evaluating the challenges, limitations and possible solutions for an upgrade. Hydraulic transients are more complex in a pump storage plant compared with a conventional hydropower plant. This applies especially in Norway, where many tunnel systems are long and complex owing to the topography. The hydraulic scale model is in scale 1:70 of the 50 MW Roskrepp hydropower plant in south Norway. This paper presents the design and scaling criteria of the model, and preliminary findings from this ongoing research project

FME HydroCen - Norsk storsatsning på vannkraft

Artikkelen beskriver aktiviteter og planer for Forskningsprogrammet HydroCen (Norwegian Research Centre for Hydropower Technology), som ble etablert ved NTNU i januar 2017 som et av åtte nye Forskningssentre for Miljøvennlig Energi (FME). HydroCen representerer en tverrfaglig satsning med deltakelse fra flere NTNU-institutter, SINTEF, NINA og alle de største vannkraftaktørene i Norge. Forskningsprogrammet har et årlig budsjett på ca. 50 mill. NOK, og finansieres med 50% fra NFR, 25% fra bransjen og 25% fra forskningspartnerne (egenbidrag). Det er allerede igangsatt og planlagt over 30 PhD og Post doc. i senteret, og ytterligere 15 er pågående i assosierte prosjekter. HydroCen omfatter fire faglige tema: 1) Vannkraftkonstruksjoner, 2) Turbin og generator, 3) Marked og tjenester og 4) Miljødesign. Det gis her en oversikt over aktivitetene i HydroCen, med spesiell vekt på prosjektene som er igangsatt innenfor tunneler og andre deler av vannveien for vannkraftanlegg

Technical Review of Existing Norwegian Pumped Storage Plants

This paper presents a technical review of the existing pumped storage plants in Norway. The power system is changing towards integrating more and more renewable energy, especially from variable renewable energy sources, leading to new challenges for the security of supply, power, frequency, and voltage regulation. Thus, energy storage options are a highly researched topic in the current situation. Even though there are many energy storage technologies, most are optimal for short term grid balancing, and few are capable of providing long term (weekly or seasonal) storage. One exception is pumped storage, a mature technology capable of delivering both short term and long term energy storage. In this paper, the ten existing pumped storage plants in Norway are presented, several of which are capable of seasonal energy storage. The Norwegian knowledge and experience with pumped storage plants technology is provided as a basis for future research within the field. The review provides information about energy production and storage capabilities, construction costs, specific costs per kW and stored kWh, electromechanical installation, technical specifications, and operational experience with focus on the design of the tunnel system layout. The data presented in this review are unique and previously unpublished. A discussion and conclusions regarding the current situation, trends, and future outlook for pumped storage plants in Norway within the European power market are provided

Technical Review of Existing Norwegian Pumped Storage Plants

This paper presents a technical review of the existing pumped storage plants in Norway. The power system is changing towards integrating more and more renewable energy, especially from variable renewable energy sources, leading to new challenges for the security of supply, power, frequency, and voltage regulation. Thus, energy storage options are a highly researched topic in the current situation. Even though there are many energy storage technologies, most are optimal for short term grid balancing, and few are capable of providing long term (weekly or seasonal) storage. One exception is pumped storage, a mature technology capable of delivering both short term and long term energy storage. In this paper, the ten existing pumped storage plants in Norway are presented, several of which are capable of seasonal energy storage. The Norwegian knowledge and experience with pumped storage plants technology is provided as a basis for future research within the field. The review provides information about energy production and storage capabilities, construction costs, specific costs per kW and stored kWh, electromechanical installation, technical specifications, and operational experience with focus on the design of the tunnel system layout. The data presented in this review are unique and previously unpublished. A discussion and conclusions regarding the current situation, trends, and future outlook for pumped storage plants in Norway within the European power market are provided