We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

A microgrid (MG) is a local entity that consists of distributed energy resources (DERs) to achieve local power reliability and sustainable energy utilization. The MG concept or renewable energy technologies integrated with energy storage systems (ESS) have gained increasing interest and popularity because it can store energy at off-peak hours and supply energy at peak hours. However, existing ESS technology faces challenges in storing energy due to various issues, such as charging/discharging, safety, reliability, size, cost, life cycle, and overall management. Thus, an advanced ESS is required with regard to capacity, protection, control interface, energy management, and characteristics to enhance the performance of ESS in MG applications. This paper comprehensively reviews the types of ESS technologies, ESS structures along with their configurations, classifications, features, energy conversion, and evaluation process. Moreover, details on the advantages and disadvantages of ESS in MG applications have been analyzed based on the process of energy formations, material selection, power transfer mechanism, capacity, efficiency, and cycle period. Existing reviews critically demonstrate the current technologies for ESS in MG applications. However, the optimum management of ESSs for efficient MG operation remains a challenge in modern power system networks. This review also highlights the key factors, issues, and challenges with possible recommendations for the further development of ESS in future MG applications. All the highlighted insights of this review significantly contribute to the increasing effort toward the development of a cost-effective and efficient ESS model with a prolonged life cycle for sustainable MG implementation.

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Review of Energy Storage System Technologies in Microgrid Applications: Issues and Challenges

The Blue Laser Diode

The role of electricity storage and hydrogen technologies in enabling global low-carbon energy transitions

Deploying storage assets to facilitate variable renewable energy integration: The impacts of grid flexibility, renewable penetration, and market structure

Valuation of energy storage in energy and regulation markets

System design and economic performance of gravity energy storage

Profitability, risk, and financial modeling of energy storage in residential and large scale applications

Dynamic modeling and design considerations for gravity energy storage

Energy storage plays a key role in providing more flexibility and balancing to the electric grid. With the increasing penetration of renewable energy technologies, there is a need to instantaneously match demand with supply. Energy storage has the potential to provide a back-up to intermittent renewable energy by storing electricity for use during more valuable periods. At this time, there are limited storage options, because several technologies are at very early stage of development. Pumped hydro energy storage is currently the most widely installed technology. This form of storage has some drawbacks which include the technology siting, as it cannot be implemented everywhere. This paper presents a concept that is similar to the existing pumped hydro storage technology. This concept is known as gravity storage, as it stores electricity in the form of gravitational potential energy. This storage option provides better operating characteristics and economically sounds solution over conventional pumped hydro storage, and can be placed almost anywhere electricity storage is needed. This paper proposes a methodology to optimally size the gravity storage technology and avoid system design failure. It also presents an economic analysis to investigate the value of this storage option. This work identifies the leveled cost of gravity storage and compares it to similar storage options.

Izeddine Zorkani

Papers

Valuation of energy storage in energy and regulation markets

System design and economic performance of gravity energy storage

Profitability, risk, and financial modeling of energy storage in residential and large scale applications

Dynamic modeling and design considerations for gravity energy storage

Sizing and economic analysis of gravity storage