abstract: This thesis addresses the issue of making an economic case for bulk energy storage in the Arizona bulk power system. Pumped hydro energy storage (PHES) is used in this study. Bulk energy storage has often been suggested for large scale electric power systems in order to levelize load (store energy when it is inexpensive [energy demand is low] and discharge energy when it is expensive [energy demand is high]). It also has the potential to provide opportunities to avoid transmission and generation expansion, and provide for generation reserve margins. As the level of renewable energy resources increases, the uncertainty and variability of wind and solar resources may be improved by bulk energy storage technologies. For this study, the MATLab software platform is used, a mathematical based modeling language, optimization solvers (specifically Gurobi), and a power flow solver (PowerWorld) are used to simulate an economic dispatch problem that includes energy storage and transmission losses. A program is created which utilizes quadratic programming to analyze various cases using a 2010 summer peak load from the Arizona portion of the Western Electricity Coordinating Council (WECC) system. Actual data from industry are used in this test bed. In this thesis, the full capabilities of Gurobi are not utilized (e.g., integer variables, binary variables). However, the formulation shown here does create a platform such that future, more sophisticated modeling may readily be incorporated. The developed software is used to assess the Arizona test bed with a low level of energy storage to study how the storage power limit effects several optimization outputs such as the system wide operating costs. Large levels of energy storage are then added to see how high level energy storage affects peak shaving, load factor, and other system applications. Finally, various constraint relaxations are made to analyze why the applications tested eventually approach a constant value. This research illustrates the use of energy storage which helps minimize the system wide generator operating cost by "shaving" energy off of the peak demand. The thesis builds on the work of another recent researcher with the objectives of strengthening the assumptions used, checking the solutions obtained, utilizing higher level simulation languages to affirm results, and expanding the results and conclusions. One important point not fully discussed in the present thesis is the impact of efficiency in the pumped hydro cycle. The efficiency of the cycle for modern units is estimated at higher than 90%. Inclusion of pumped hydro losses is relegated to future work. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

abstract: This thesis addresses the issue of making an economic case for energy storage in power systems. Bulk energy storage has often been suggested for large scale electric power systems in order to levelize load; store energy when it is inexpensive and discharge energy when it is expensive; potentially defer transmission and generation expansion; and provide for generation reserve margins. As renewable energy resource penetration increases, the uncertainty and variability of wind and solar may be alleviated by bulk energy storage technologies. The quadratic programming function in MATLAB is used to simulate an economic dispatch that includes energy storage. A program is created that utilizes quadratic programming to analyze various cases using a 2010 summer peak load from the Arizona transmission system, part of the Western Electricity Coordinating Council (WECC). The MATLAB program is used first to test the Arizona test bed with a low level of energy storage to study how the storage power limit effects several optimization out-puts such as the system wide operating costs. Very high levels of energy storage are then added to see how high level energy storage affects peak shaving, load factor, and other system applications. Finally, various constraint relaxations are made to analyze why the applications tested eventually approach a constant value. This research illustrates the use of energy storage which helps minimize the system wide generator operating cost by "shaving" energy off of the peak demand. / Dissertation/Thesis / M.S. Electrical Engineering 2013

In the last decade, the power generation mix and the energy markets have been affected by the growing development of distributed and renewable energy sources.Nevertheless, a significant drawback of solar and wind energy is their intermittent and weather-dependent production, which often leads to a mismatch between renewable energy production and its use. Thus, the need for energy storage is recently emerging and becoming more relevant in this era of the energy transition. Among several technologies, today, pumped hydro energy storage (PHES) represents the largest share of the energy storage systems in the world. However, possible new investors, who might be attracted by potential profit in PHES, are repelled bythe long payback period and the scarcity of adequate site topology for such power plants. Relevant design decisions can be taken to reduce the costs and improve the performance or to escape the PHES topographical requirements. For this reason, the first part of this PhD thesis reviews and provides potential assessments of some unconventional PHES systems, applied in synergy with existing infrastructures. Such is the standpoint of micro facilities near waterway locks, or underground cavities used as lower reservoirs (UPSH), or the use of pump-turbines at variable geometryto cope with fluctuating loads.Moreover, important information on PHES in micro-scale is largely missing and their potential in distributed energy systems still needs to be unveiled. In the attempt to fill this gap, this thesis provides a techno-economic overview of the design and characterization of a first-of-its-kind PHES micro facility. In micro-scales hydropower projects, the initial capital cost of a conventional hydroelectric unit is hard to be determined and often economically prohibitive. Interestingly, in order to cut the total capital investment, the micro-PHES prototype runs with a single centrifugal pump for both pumping and generating phases and exploits existing stormwater reservoirs. The variable speed regulation is also implemented and it allows the pump to constantly operate at the maximum hydraulic efficiency in order to deal with load variations. In the same way, the pump working in reverse, namely pump as turbine (PaT), runs at the most suitable speed and it keeps a high efficiency over a wide load range. In addition, the analysis of the techno-economic parameters for such a system provides an important dataset for micro-PHES feasibility breakdown.PaTs are a legitimate cost-effective option in micro hydropower but an universal performance prediction does not exist. Their hydraulic efficiency can possibly shift from the higher efficiency of traditional hydraulic turbines. Nowadays, these reasons restrict PaTs exploitation. In this thesis, a multivariate regression method is applied to the CFD results to build a surrogate model of the PaT hydraulic characteristics as a function of the cutwater geometrical modifications. Based on this model, an optimization problem is solved to identify the most advantageous geometrical assetof the PaT cutwater to maximize the hydraulic efficiency. The presented methodology and design optimization of the cutwater in PaTs, which are extremely suited to our current energy generation needs, provides a unique and much-sought guide to its performance, improvements, and adaptation to hydropower. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Pumped hydro energy storages commonly plan their operations on short-term forecasts of the upcoming electricity prices, meaning that errors in these forecasts would entail suboptimal operations of the energy storage. Despite the high investment costs of pumped hydro energy storages, few studies take a holistic approach to the uncertainties involved in such investment decisions. The aim of this study is to investigate how forecast errors in electricity prices affect the chosen size configuration in investment decisions for pumped hydro energy storages. Moreover, sizing decisions are made in the long-term and involve long-term uncertainties in electricity prices. A robust decision-making framework including long-term electricity price scenarios is therefore used to evaluate the effects of including forecast errors in the sizing decision. By simulating the day-to-day operation of the energy storage with short-term forecasts, the effects of including the errors are compared to using perfect information. Using this approach, the most robust capacity is shown to increase by 25 MW, from 2 375 MW to 2 400 MW, when including forecast errors instead of assuming perfect information in the simulations. This indicates that the deviations in short-term forecasts require the pumped hydro energy storage operator to be more flexible in their operations, thus requiring a higher capacity. In addition, the profitability of the energy storage decreased significantly when including forecast errors in the simulations, showing the importance of taking the short-term forecast errors into account in sizing and investment decisions of pumped hydro energy storage. / Driften av pumpkraftverk optimeras med hjälp av kortsiktiga prognoser av elpriser, vilket innebär att fel i dessa prognoser leder till suboptimal drift. Trots att investeringar i pumpkraftverk är kostsamma, har få studier ett holistisk synsätt kring osäkerheter i investeringsbeslutet. Målet med denna studie är att undersöka hur kortsiktiga prognosfel i elpriser påverkar den optimala dimensionering av pumpkraftverk. Investeringsbeslut i pumpkraftverk är långsiktiga och kräver estimat av framtida elpriser, vars karakteristik är osäker. Ett ramverk som bygger på robust beslutstagande, med scenarier över framtida elpriser, används därför för att bedöma effekten av att inkludera kortsiktiga prognosfel i investeringsbeslutet. Genom att simulera den dagliga driften av energilager, undersöks effekten av att inkludera prognosfel jämfört med perfekt information. Med detta tillvägagångsätt ökade den mest robusta kapaciteten med 25 MW, från 2 375 MW till 2 400 MW, när prognosfel inkluderades. Detta visar på att fel i kortsiktiga prognoser kräver pumpkraftverket av vara mer flexibelt, vilket ges av höjdkapacitet. Lönsamheten minskade också signifikant när prognosfel inkluderades, vilket visar på vikten av att ta hänsyn till kortsiktiga prognosfel i beslut kring dimensionering och investering av pumpkraftverk.