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Energy Storage Technologies for Microgrids
Published in Stephen A. Roosa, Fundamentals of Microgrids, 2020
Pumped hydro storage is an alternative that recycles the water repeatedly at the same site. A pumped storage hydroelectric plant uses two or more reservoirs, with at least one located at a much higher elevation than the other. The reservoir at lower elevation is called the lower reservoir and the one at higher elevation is called the upper reservoir. The storage concept involves reusing the water from the lower reservoir (after it has passed through the turbines) by pumping it to the upper reservoir to generate additional electricity. This type of energy storage system uses excess electricity, usually generated by the hydropower site, to pump water to higher altitude where it is stored as gravitational potential energy [2]. During periods of low demand for electricity, such as nights and weekends, water is stored by reversing the turbines (or providing an alternative water pumping system) and pumping the water from the lower to the upper reservoir. The stored water is later released, passes through the penstock, turns the turbines, and generates electricity as gravity causes it to flow back into the lower reservoir. The round-trip efficiency of pumped hydro systems is between 75% and 78% [2]. The energy losses are mostly due to the inefficiency of pumping water from a lower to a higher elevation against the force of gravity. However, pumped storage plants have higher operating costs than conventional hydropower plants due to the added equipment and costs associated with pumping water uphill to refill the upper reservoirs [6].
Infiltration and soil moisture
Published in Stephen A. Thompson, Hydrology for Water Management, 2017
Applying this terminology the two sources of energy acting on soil water are the gravitational potential ψz and the pressure or matric potential ψp. The gravitational potential is the potential energy due to the acceleration of gravity. It is equal to the weight of the water γ times its elevation z above some reference plane. The gravitational potential is significant only when the soil moisture level exceeds the field capacity, i.e. when ψp > −0.33 bars, otherwise the pressure potential dominates. The pressure potential is what we have previously called capillary suction or tension – it is the potential energy due to the attraction of water for soil particles. If we ignore some other very small potentials, we can assume that the sum of the gravitational potential and pressure potential equals the total soil moisture potential ψ: () ψ=ψz+ψp
Single Degree-of-Freedom Vibration: General Loading and Advanced Topics
Published in Haym Benaroya, Mark Nagurka, Seon Han, Mechanical Vibration, 2017
Haym Benaroya, Mark Nagurka, Seon Han
Solution Part Two: The second part of this solution is the determination of the drop height that results in loads and displacements similar to the 3g decaying sinusoid. This drop height will be used to design an experiment to verify compliance with design requirements. The height will be determined using the single degree‐offreedom model just developed. From basic physics, when an object is dropped from rest at height h, its gravitational potential energy is converted to kinetic energy, and at the instant of impact, mgh=mv02/2 $ mgh = mv_{0}^{2} /2 $ , from which v0=2gh. $$ v_{0} = \sqrt {2gh} . $$
Mapping debris flow susceptibility based on watershed unit and grid cell unit: a comparison study
Published in Geomatics, Natural Hazards and Risk, 2019
Shengwu Qin, Jiangfeng Lv, Chen Cao, Zhongjun Ma, Xiuyu Hu, Fei Liu, Shuangshuang Qiao, Qiang Dou
The elevation ranges between 182 and 1386.64 m in the study area (Figure 3a). The elevation reflects the relative height difference, which aids in determining the gravity potential energy of the debris flow. The larger the height difference, the greater the gravitational potential energy. This provides a dynamic condition for the occurrence of a debris flow. For the WU, the difference between the highest and the lowest points in each watershed was calculated and used as influencing factor.