The benefits and challenges of renewables on the electric grid and opportunities for systems integration and demand side management

Environmental policies, reduced manufacturing costs, and technology improvements have all contributed to the growing installation of wind turbines and solar photovoltaic arrays in the electric grid. While these new sources of renewable electrical power provide environmental and economic benefits to the electric grid, they also complicate the balancing of supply and demand required to reliably operate the grid. The seasonal, daily, and sub-hourly fluctuations in the energy output of wind and solar generators must be compensated by operating the existing power plant fleet more flexibly or by providing more flexible sources of electricity demand. This dissertation categorizes and quantifies this compensation by studying the "flexibility requirements'' imposed by wind and solar generation, approximates the economically optimal capacities of regional wind and solar resources in the grid, and explores the ability of a central utility plant to add a flexible source of demand to the electric grid system. These topics are covered in the four chapters described below. Chapter 3 utilizes a unit commitment and dispatch (UC&D) model to simulate large solar generation assets with different geographic locations and orientations. The simulations show the sensitivity of the wholesale energy price, reserve market prices, total dispatch cost, fuel mix, emissions, and water use to changes in net load flexibility requirements. The results show that generating 22,500 GWh of solar energy in a 2011 simulation of the Electric Reliability Council of Texas (ERCOT) reduces total dispatch cost by approximately $900 Million (a 10.3$10 Million (a 3% increase). The results also show that solar PV reduces water consumption, water withdrawals, and CO₂, NO [subscript x], and SO [subscript x] emissions. Installing sufficient solar panel capacity to generate that much electricity also reduces peak load by 4% but increases net load volatility by 40--79% and ramping by 11--33%. In addition, west-located, west-oriented solar resources reduce total dispatch cost more than the other simulated solar scenarios. The west-located, west-oriented solar simulation required greater system flexibility, but utilized more low-cost generators and fewer high-cost generators for energy production than other simulated scenarios. These results suggest that the mix of energy provided by different generation technologies influences the dispatch cost more than the net load flexibility requirements. Chapter 4 develops a quantitative framework for calculating flexibility requirements and performs a statistical analysis of load, wind, and solar data from the Electric Reliability Council of Texas (ERCOT) to show how wind and solar capacity impacts these grid flexibility requirements. Growing wind capacity shows only minor correlation with increasing flexibility requirements, but shows some correlation with ramp down rates and daily volatility in the net load. Growing solar capacity shows a direct correlation with increasing flexibility requirements if load patterns do not change. While adding 15.7 GW of wind power had only minor effects on system flexibility requirements, adding 14.5 GW of solar to the ERCOT grid increases maximum 1-hr ramp rates by 135%, 3-hr ramp rates by 30%, ramp factors by 140%, 1-hr volatility by 100%, and 1-day volatility by 30%. Wind and solar impact flexibility requirements at different times of the day: wind tends to intensify demand-driven flexibility events by ramping up energy production at night when demand is decreasing and ramping down energy production in the morning when demand is increasing, while solar tends to intensify flexibility requirements due to its quick changes in energy output driven by the rising and setting sun. Adding wind to a system with large amounts of solar does not tend to increase flexibility requirements except for the daily volatility. The geographic location and orientation of solar arrays also influences flexibility requirements, with fixed, southeast-facing panels providing a significant reduction. These results can inform strategies for managing the grid flexibility requirements created by growing renewable capacity. Chapter 5 develops a model for calculating the optimal amount of transmission, wind, and solar capacity that should be built in a grid's different regions. It also presents a framework for choosing CO₂ prices by balancing increasing system cost and flexibility requirements with CO₂ emissions reductions. In a simulation of the ERCOT grid, the model suggests a 60 $/ton CO₂ price and an optimal investment of 27.0 GW of transmission capacity to five different regions. These regions install a total of 26.6 GW of wind and 11.1 GW of solar, representing a grid with about 60% thermal and 40% renewable capacity. This renewable mix produces 110 TWh of energy per year, 34% of the total electricity demand. The grid emits 82.2 million tons of CO₂ per year under this scenario, a 65% reduction from the 237 million tons produced when no renewable capacity is installed. At the optimal renewable development solution, all coal and natural gas boiler generators have capacity factors less than 20% with many of them not being dispatched at all. While these results are specific to ERCOT, the methods and model can be used by any grid considering renewable energy capacity expansion. Chapter 6 develops a mixed-integer linear program for modeling the optimal equipment capacity and dispatch of a central utility plant (CUP) in a residential neighborhood and its ability to improve rooftop solar integration. The CUP equipment includes a microturbine, battery, chiller plant, and cooling storage. The CUP model is exposed to a variety of electricity rate structures to see how they influence its operation. The model finds the optimal capacity for each piece of CUP equipment, optimizing their hourly dispatch to meet neighborhood cooling and electric demand while maximizing profit. In an Austin, TX, USA base case, the neighborhood benefits economically by including the CUP, although the CUP demonstrates limited potential to integrate high penetrations of rooftop solar resources. While peak demand and reverse power flows are reduced under all tested rate structures, the CUP worsens net demand ramp rates. A time-of-use rate with no demand charge and moderate differences between off-peak and on-peak prices balances the output parameters, reducing reverse power flows by 43%, peak demand by 51%, and annual cost by 9.1% versus the ``No CUP'' base case while limiting net demand ramp rate increase to 84% more than the base case. Building a clean, resilient, and reliable electric grid for the future is a worthwhile endeavor that will require innovative supply-side and demand-side solutions for integrating the intermittent power output of renewable generation into the electric grid. As a cohesive document, this dissertation communicates the scale and severity of the flexibility requirements that will be required to operate systems with large amounts of wind and solar generation and explores one demand-side method for providing that needed flexibility. There are many opportunities to expand these analyses and explore new sources of grid flexibility in future work.Mechanical Engineerin

Dont Mess with Texas: Getting the Lone Star State to Net-Zero by 2050

The world is decarbonizing. Many countries, companies, and financial institutions have committed to cutting their emissions. Decarbonization commitments have been issued by: 136 countries including Canada, China, and the UK, at least 16 U.S. states including New York, Louisiana, and Virginia, and a third of the largest 2,000 publicly traded companies in the world, including Apple, Amazon, and Walmart, and numerous Texas companies like ExxonMobil, American and Southwest Airlines, Baker Hughes, and AT&T.1–9 These decarbonizing countries, states, cities, and companies are Texas's energy customers. If Texas ignores the challenge to decarbonize its economy, it may eventually face the more difficult challenge of selling carbon-intensive products to customers around the world who do not want them. We are already seeing this scenario beginning to play out with France canceling a liquified natural gas deal from Texas gas producers and both U.S. and international automakers announcing shifts to electric vehicles. Proactive net-zero emissions strategies might allow Texas to maintain energy leadership and grow the economy within a rapidly decarbonizing global marketplace.Thankfully, Texas is uniquely positioned to lead the world in the transition to a carbon-neutral energy economy. With the second highest Gross State Product in the US, the Texas economy is on par with countries like Canada, Italy, or Brazil. Thus, Texas's decisions have global implications. Texas also has an abundant resource of low-carbon energy sources to harness and a world-class workforce with technical capabilities to implement solutions at a large-scale quickly and safely. Texas has a promising opportunity to lead the world towards a better energy system in a way that provides significant economic benefits to the state by leveraging our renewable resources, energy industry expertise, and strong manufacturing and export markets for clean electricity, fuels, and products. The world is moving, with or without Texas, but it is likely to move faster--and Texas will be more prosperous--if Texans lead the way.There are many ways to fully decarbonize the Texas economy across all sectors by 2050. In this analysis, we present a Business as Usual (BAU) scenario and four possible pathways to Texas achieving state-wide net-zero emissions by 2050. Figure ES-1 provides a visual comparison of scenario conditions

Physiological response to firefighting activities of various work cycles using extended duration and prototype SCBA

Firefighters’ self-contained breathing apparatus (SCBA) protects the respiratory system during firefighting but increases the physiological burden. Extended duration SCBA (>30 min) have increased air supply, potentially increasing the duration of firefighting work cycles. To examine the effects of SCBA configuration and work cycle (length and rest), 30 firefighters completed seven trials using different SCBA and one or two bouts of simulated firefighting following work cycles common in the United States. Heart rate, core temperature, oxygen consumption, work output and self-reported perceptions were recorded during all activities. Varying SCBA resulted in few differences in these parameters. However, during a second bout, work output significantly declined while heart rates and core temperatures were elevated relative to a single bout. Thirty seven per cent of the subjects were unable to complete the second bout in at least one of the two-bout conditions. These firefighters had lower fitness and higher body mass than those who completed all assigned tasks. Practitioner Summary: The effects of extended duration SCBA and work/rest cycles on physiological parameters and work output have not been examined. Cylinder size had minimal effects, but extended work cycles with no rest resulted in increased physiological strain and decreased work output. This effect was more pronounced in firefighters with lower fitness.This work was supported by the Department of Homeland Security Fire Prevention and Safety, Federal Emergency Management Agency [grant number EMW-2010-FP-01606].Ope

US residential heat pumps: the private economic potential and its emissions, health, and grid impacts

To explore electrification as a climate change mitigation strategy, we study US residential heat pump adoption, given the current US housing stock. Our research asks (a) how the costs and benefits of heat pump adoption evolve with increased penetration, (b) what rate of heat pump adoption is economic given today’s housing stock, electric grid, energy prices, and heat pump technology, and (c) what effect changing policies, innovations, and technology improvements might have on heat pump adoption. We answer these research questions by simulating the energy consumption of 400 representative single-family houses in each of 55 US cities both before and after heat pump adoption. We use energy prices, CO _2 emissions, health damages from criteria air pollutants, and changes in peak electricity demand to quantify the costs and benefits of each house’s heat pump retrofit. The results show that 32% of US houses would benefit economically from installing a heat pump, and 70% of US houses could reduce emissions damages by installing a heat pump. We show that the potential for heat pump adoption varies depending on electric grid, climate, baseline heating fuel, and housing characteristics. Based on these results we identify strategic, technology, and policy insights to stimulate high heat pump adoption rates and deep electrification of the US residential heating sector, which reduces CO _2 emissions and the impacts of climate change

Renewable Electrolysis in Texas: Pipelines versus Power Lines

Using wind and solar generation to power electrolysis facilities and produce “green” hydrogen at scale would require infrastructure investment. Using current technology, we identify at least one situation in which producing hydrogen at the point of electricity generation and transporting it to the point of use via pipeline costs about one third that of transmitting the electricity and generating hydrogen at the point of use. This raises the possibility that hydrogen pipelines might provide an alternative to high voltage transmission lines for connecting renewable generation with demand. In this white paper, we explore the tradeoffs of those two options

High-pitch coronary CT angiography with third generation dual-source CT: limits of heart rate

To determine the average heart rate (HR) and heart rate variability (HRV) required for diagnostic imaging of the coronary arteries in patients undergoing high-pitch CT-angiography (CTA) with third-generation dual-source CT. Fifty consecutive patients underwent CTA of the thoracic (n = 8) and thoracoabdominal (n = 42) aorta with third-generation dual-source 192-slice CT with prospective electrocardiography (ECG)-gating at a pitch of 3.2. No β-blockers were administered. Motion artifacts of coronary arteries were graded on a 4-point scale. Average HR and HRV were noted. The average HR was 66 ± 11 beats per minute (bpm) (range 45-96 bpm); the HRV was 7.3 ± 4.4 bpm (range 3-20 bpm). Interobserver agreement on grade of image quality for the 642 coronary segments evaluated by both observers was good (κ = 0.71). Diagnostic image quality was found for 608 of the 642 segments (95 %) in 43 of 50 patients (86 %). In 14 % of the patients, image quality was nondiagnostic for at least one segment. HR (p = 0.001) was significantly higher in patients with at least one non-diagnostic segment compared to those without. There was no significant difference (p > 0.05) in HRV between patients with nondiagnostic segments and those with diagnostic images of all segments. All patients with a HR < 70 bpm had diagnostic image quality in all coronary segments. The effective radiation dose and scan time for the heart were 0.4 ± 0.1 mSv and 0.17 ± 0.02 s, respectively. Third-generation dual-source 192-slice CT allows for coronary angiography in the prospectively ECG-gated high-pitch mode with diagnostic image quality at HR up to 70 bpm. HRV is not significantly related to image quality of coronary CTA

Review on uremic toxins : classification, concentration, and interindividual variability

Background. The choice of the correct concentration of potential uremic toxins for in vitro, ex vivo, and in vivo experiments remains a major area of concern; errors at this level might result in incorrect decisions regarding therpeutic correction of uremia and related clinical complications. Methods. An encyclopedic list of uremic retention solutes was composed, containing their mean normal concentration (C-N), their highest mean/median uremic concentration (C-U), their highest concentration ever reported in uremia (C-MAX), and their molecular weight. A literature search of 857 publications on uremic toxicity resulted in the selection of data reported in 55 publications on 90 compounds, published between 1968 and 2002. Results. For all compounds, C-U and/or C-MAX exceeded C-N. Molecular weight was lower than 500 D for 68 compounds; of the remaining 22 middle molecules, 12 exceeded 12,000 D. C-U ranged from 32.0 ng/L (methionine-enkephalin) up to 2.3 g/L (urea). C-U in the ng/L range was found especially for the middle molecules (10/22; 45.5%), compared with 2/68 (2.9%) for a molecular weight <500 D (P < 0.002). Twenty-five solutes (27.8%) were protein bound. Most of them had a molecular weight <500 D except for leptin and retinol-binding protein. The ratio C-U/C-N, an index of the concentration range over which toxicity is exerted, exceeded 15 in the case of 20 compounds. The highest values were registered for several guanidines, protein-bound compounds, and middle molecules, to a large extent compounds with known toxicity. A ratio of C-MAX /C-U <4, pointing to a Gaussian distribution, was found for the majority of the compounds (74/90; 82%). For some compounds, however, this ratio largely exceeded 4 [e.g., for leptin (6.81) or indole-3-acetic acid (10.37)], pointing to other influencing factors than renal function, such as gender, genetic predisposition, proteolytic breakdown, posttranslation modification, general condition, or nutritional status. Conclusion. Concentrations of retention solutes in uremia vary over a broad range, from nanograms per liter to grams per liter. Low concentrations are found especially for the middle molecules. A substantial number of molecules are protein bound and/or middle molecules, and many of these exert toxicity and are characterized by a high range of toxic over normal concentration (C-U/C-N ratio). Hence, uremic retention is a complex problem that concerns many more solutes than the current markers of urea and creatinine alone. This list provides a basis for systematic analytic approaches to map the relative importance of the enlisted families of toxins