Unit-Contingent Power Purchase Agreement and Asymmetric Information about Plant Outage

This paper analyzes a unit-contingent power purchase agreement between an electricity distributor and a power plant. Under such a contract the distributor pays the plant a fixed price if the plant is operational and nothing if plant outage occurs. Pricing a unit-contingent contract is complicated by the fact that the plant’s true status is its private information. The difference between the electricity spot price and the unit-contingent contract price provides an incentive for the plant to misreport its status and earn profit at the distributor’s expense. To prevent misreporting, the distributor may inspect the plant and levy penalties if misreporting is discovered. We find that some type of misreporting under certain circumstances can benefit both the plant and the distributor, because it serves as a risk-allocation mechanism between the two parties. We show that such a risk-allocation mechanism is equivalent to using state-contingent options and prohibiting misreporting.http://deepblue.lib.umich.edu/bitstream/2027.42/61470/1/1120_OWu.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/61470/4/1120_may09_OWu.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/61470/6/1120_Aug11_Wu.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/61470/8/1120_Wu_Oct11.pd

Seasonal Energy Storage Operations with Limited Flexibility

The value of seasonal energy storage depends on how the firm best operates the storage to capture the seasonal price spread. Energy storage operations typically face limited operational flexibility characterized by the speed of storing and releasing energy. A widely used practice-based heuristic, the rolling intrinsic (RI) policy, generally performs well, but can significantly underperform in some cases. In this paper, we aim to understand the gap between the RI policy and the optimal policy, and design improved heuristic policies to close or reduce this gap. A new heuristic policy, the “price-adjusted rolling intrinsic (PARI) policy,” is developed based on theoretical analysis of the value of storage options. This heuristic adjusts prices before applying the RI policy, and the adjusted prices inform the RI policy about the values of various storage options. Our numerical experiments show that the PARI policy is especially capable of recovering high value losses of the RI policy. For the instances where the RI policy loses more than 4% of the optimal storage value, the PARI policy on average is able to recover more than 90% of the value loss.http://deepblue.lib.umich.edu/bitstream/2027.42/85788/1/1160_Wu.pd

Energy-Efficient Transmission Scheduling with Strict Underflow Constraints

We consider a single source transmitting data to one or more receivers/users over a shared wireless channel. Due to random fading, the wireless channel conditions vary with time and from user to user. Each user has a buffer to store received packets before they are drained. At each time step, the source determines how much power to use for transmission to each user. The source's objective is to allocate power in a manner that minimizes an expected cost measure, while satisfying strict buffer underflow constraints and a total power constraint in each slot. The expected cost measure is composed of costs associated with power consumption from transmission and packet holding costs. The primary application motivating this problem is wireless media streaming. For this application, the buffer underflow constraints prevent the user buffers from emptying, so as to maintain playout quality. In the case of a single user with linear power-rate curves, we show that a modified base-stock policy is optimal under the finite horizon, infinite horizon discounted, and infinite horizon average expected cost criteria. For a single user with piecewise-linear convex power-rate curves, we show that a finite generalized base-stock policy is optimal under all three expected cost criteria. We also present the sequences of critical numbers that complete the characterization of the optimal control laws in each of these cases when some additional technical conditions are satisfied. We then analyze the structure of the optimal policy for the case of two users. We conclude with a discussion of methods to identify implementable near-optimal policies for the most general case of M users.Comment: 109 pages, 11 pdf figures, template.tex is main file. We have significantly revised the paper from version 1. Additions include the case of a single receiver with piecewise-linear convex power-rate curves, the case of two receivers, and the infinite horizon average expected cost proble

Supply Function Competition in Electricity Markets with Flexible, Inflexible, and Variable Generation

In this paper we study the supply function competition between power-generation firms with different levels of flexibility. Inflexible firms produce power at a constant rate over an operating horizon, while flexible firms can adjust their output to meet the fluctuations in electricity demand. Both types of firms compete in an electricity market by submitting supply functions to a system operator, who solves an optimal dispatch problem to determine the production level for each firm and the corresponding market price. We study how firms’ (in)flexibility affects their equilibrium behavior and the market price. We also analyze the impact of variable generation (such as wind and solar power) on the equilibrium, with the focus on the effects of the amount of variable generation, its priority in dispatch, and the production- based subsidies. We find that the classic supply function equilibrium model overestimates the intensity of the market competition, and even more so as more variable generation is introduced into the system. The policy of economically curtailing variable generation intensifies the market competition, reduces price volatility, and improves the system’s overall efficiency. Moreover, we show that these benefits are most significant in the absence of the production-based subsidies.http://deepblue.lib.umich.edu/bitstream/2027.42/102571/1/2014Jan28OWu.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102571/4/1218_Wu_Apr14.pd

The contribution of distant sources to the observed flux of ultra high-energy cosmic rays

Ultra-high-energy (UHE) cosmic rays (CRs) interact with cosmic background radiation through hadronic processes, and the Universe would become 'opaque' to UHE CRs of energies ∼(1018-1020) eV over about several tens of Mpc, setting the Greisen-Zatsepin-Kuz'min (GZK) horizon. We demonstrate that a non-negligible fraction of the UHE CRs arriving on Earth could originate from beyond the GZK horizon when heavy nuclear CRs, and the population and evolution of UHE CR sources are taken into account. We show how the multi-particle CR horizon is modified by different source populations, and discuss how this leads to the natural emergence of an isotropic flux component in the observed UHE CR background. This component would coexist with an anisotropic foreground component contributed by nearby sources within the GZK horizon

Does Renewable Energy Renew the Endeavor in Energy Efficiency?

Improvement in energy efficiency (EE) has slowed globally since 2015 and is now falling short of the 2.6% per year target recommended by the United Nations Sustainable Development Goals, despite an abundance of EE opportunities. Barriers to EE have existed long before the rise in renewable energy (RE) investment. However, increased RE adoption may have unintended consequences for improving EE as adoption may raise or lower the barriers to EE. In this paper, we examine whether and how RE adoption can increase or decrease EE improvement. On the one hand, RE represent a competitor to EE for managerial attention and budget. On the other, the adoption of RE may increase the overall awareness of energy usage and drive EE improvement. Using site-level data from an industrial conglomerate, we estimate the impact of changes in RE usage and in the acquisition approach on the EE of 183 manufacturing sites across the globe from 2015 to 2020. On average, we find that using RE to meet 10% more of a site’s energy demand led to an additional 2.0% improvement in EE. However, there is significant heterogeneity in the effects depending on the acquisition approach. We find that while purchasing RE credits or entering into power purchase agreements led to gains in EE, installing on-site RE generators had no effect. To understand these gains, we surveyed site managers regarding their attitudes and intentions. The results suggest that there was a greater focus on EE by both managers and workers after increasing their RE usage. We also find quantitative evidence of managers submitting more budget requests for EE improvements in the twelve months following increases in RE. For corporations looking to use more RE, we offer evidence of additional returns in the form of energy savings, but realizing them requires careful consideration of the acquisition approach of RE

102 fs pulse generation from a long-term stable, inkjet-printed black phosphorus-mode-locked fiber laser.

We demonstrate a long-term stable, all-fiber, erbium-doped femtosecond laser mode-locked by a black phosphorus saturable absorber. The saturable absorber, fabricated by scalable and highly controllable inkjet printing technology, exhibits strong nonlinear optical response and is stable for long-term operation against intense irradiation, overcoming a key drawback of this material. The oscillator delivers self-starting, 102 fs stable pulses centered at 1555 nm with 40 nm spectral bandwidth. This represents the shortest pulse duration achieved from black phosphorus in a fiber laser to date. Our results demonstrate the great potential for black phosphorus as an excellent candidate for long-term stable ultrashort pulse generation

Free-troposphere ozone and carbon monoxide over the North Atlantic for 2001-2011

In situ measurements of carbon monoxide (CO) and ozone (O3) at the Pico Mountain Observatory (PMO) located in the Azores, Portugal, are analyzed together with results from an atmospheric chemical transport model (GEOS-Chem) and satellite remote sensing data (AIRS (Atmospheric Infrared Sounder) for CO, and TES (Tropospheric Emission Spectrometer) for O3) to examine the evolution of free-troposphere CO and O3 over the North Atlantic for 2001-2011. GEOS-Chem captured the seasonal cycles for CO and O3 well but significantly underestimated the mixing ratios of CO, particularly in spring. Statistically significant (using a significance level of 0.05) decreasing trends were found for both CO and O3 based on harmonic regression analysis of the measurement data. The best estimates of the possible trends for CO and O3 measurements are -0.31 ± 0.30 (2-σ) ppbv yr-1 and -0.21 ± 0.11 (2-σ) ppbv yr-1, respectively. Similar decreasing trends for both species were obtained with GEOS-Chem simulation results. The most important factor contributing to the decreases in CO and O3 at PMO over the past decade is the decline in anthropogenic emissions from North America, which more than compensate for the impacts from increasing Asian emissions. It is likely that climate change in the past decade has also affected the intercontinental transport of O3

Diagnosing Stagnant Gas Bubbles in a Polymer Electrolyte Membrane Water Electrolyser using Acoustic Emission

The use of acoustic emission as a low-cost, non-destructive, and operando diagnostic tool has been demonstrated for a range of electrochemical energy conversion and storage devices, including polymer electrolyte membrane water electrolysers (PEMWEs) and fuel cells. In this work, an abrupt change in acoustic regime is observed during operation of a PEMWE as the current density is increased from 0.5 to 1.0 A cm^{-2}. This regime change is marked by a sudden drop in the number of acoustic hits, while hit duration, amplitude, and energy increase significantly. It is found that the change in acoustic regime coincides with a significant extension of the stagnant bubble region in the flow channels of the PEMWE, observed with high-speed optical imaging. These results demonstrate that acoustic emission can be used effectively as an operando diagnostic tool to monitor bubble formation (two-phase flow conditions) in PEMWEs, facilitating rapid testing or prototyping, and contributing to operational safety

The Unreasonable Effectiveness of Encoder-Decoder Networks for Retinal Vessel Segmentation

We propose an encoder-decoder framework for the segmentation of blood vessels in retinal images that relies on the extraction of large-scale patches at multiple image-scales during training. Experiments on three fundus image datasets demonstrate that this approach achieves state-of-the-art results and can be implemented using a simple and efficient fully-convolutional network with a parameter count of less than 0.8M. Furthermore, we show that this framework - called VLight - avoids overfitting to specific training images and generalizes well across different datasets, which makes it highly suitable for real-world applications where robustness, accuracy as well as low inference time on high-resolution fundus images is required