550 research outputs found
Operation of Cool Thermal Energy Storage to Increase Renewable Energy Utilization
Recent international agreements on climate change aim to increase the production of electricity derived from renewable energy resources. Renewable energy generation can be pursued on both an individual building and utility scale. Due to the intermittent nature of renewables, some form of energy storage is essential to bridge diurnal mismatches between generation and demand. Air-conditioning loads associated with commercial buildings dominate peak electricity demand on the utility grid in some areas and climates. Therefore, Cool Thermal Energy Storage (CTES) is a relatively technically mature and inexpensive means of providing this “storage†and balancing supply/demand mismatches, thereby enabling the success of increased renewable energy penetration. Electrical energy generated by renewables during periods of higher availability can be used to run chillers that charge CTES systems. The stored thermal energy can subsequently be used to meet air-conditioning demand during periods of low renewable energy resource availability.  In this work, the U.S. Department of Energy Commercial Reference Building Model for a secondary school is used to obtain simulated cooling loads that are met by a combination of two chillers and a stratified chilled water thermal storage system. Control strategies are designed to charge the thermal storage system when renewable resources are available and discharge storage to meet building cooling loads during periods with low or no renewable energy resource. One optimization target is the fraction of the chiller energy consumption met by renewable power. This metric is one that may be of interest to electric utilities trying to manage a grid with increasing renewable penetration. An alternative optimization target is the net economic benefit to the building owner assuming on-site, small scale renewable generation and thermal storage. This metric is based on equipment costs, net electric demand after wind and/or solar generation offsets the chiller electric demand, and time-of-use electricity rate structures.  The results show that there is a trade-off between maximizing the use of renewable power and life-cycle cost, but a storage system designed to optimize either variable will be more cost effective and utilize the renewable resource better than a system without storage. The analysis is carried out for locations in Texas and California. These results suggest that CTES may be a technology enabling utilities to reach higher penetration of renewables while avoiding the so-called “duck curve†generation ramp caused by the time mismatch between the renewable generation and demand peaks
Highly indistinguishable single photons from incoherently and coherently excited GaAs quantum dots
Semiconductor quantum dots are converging towards the demanding requirements
of photonic quantum technologies. Among different systems, quantum dots with
dimensions exceeding the free-exciton Bohr radius are appealing because of
their high oscillator strengths. While this property has received much
attention in the context of cavity quantum electrodynamics, little is known
about the degree of indistinguishability of single photons consecutively
emitted by such dots and on the proper excitation schemes to achieve high
indistinguishability. A prominent example is represented by GaAs quantum dots
obtained by local droplet etching, which recently outperformed other systems as
triggered sources of entangled photon pairs. On these dots, we compare
different single-photon excitation mechanisms, and we find (i) a "phonon
bottleneck" and poor indistinguishability for conventional excitation via
excited states and (ii) photon indistinguishablilities above 90% for both
strictly resonant and for incoherent acoustic- and optical-phonon-assisted
excitation. Among the excitation schemes, optical phonon-assisted excitation
enables straightforward laser rejection without a compromise on the source
brightness together with a high photon indistinguishability
Entanglement swapping with photons generated on-demand by a quantum dot
Photonic entanglement swapping, the procedure of entangling photons without
any direct interaction, is a fundamental test of quantum mechanics and an
essential resource to the realization of quantum networks. Probabilistic
sources of non-classical light can be used for entanglement swapping, but
quantum communication technologies with device-independent functionalities
demand for push-button operation that, in principle, can be implemented using
single quantum emitters. This, however, turned out to be an extraordinary
challenge due to the stringent requirements on the efficiency and purity of
generation of entangled states. Here we tackle this challenge and show that
pairs of polarization-entangled photons generated on-demand by a GaAs quantum
dot can be used to successfully demonstrate all-photonic entanglement swapping.
Moreover, we develop a theoretical model that provides quantitative insight on
the critical figures of merit for the performance of the swapping procedure.
This work shows that solid-state quantum emitters are mature for quantum
networking and indicates a path for scaling up.Comment: The first four authors contributed equally to this work. 17 pages, 3
figure
- …