Characterization of Wind Power Resource in the United States and its Intermittency

http://globalchange.mit.edu/research/publications/2221Wind resource in the continental and offshore United States has been reconstructed and characterized using metrics that describe, apart from abundance, its availability, persistence and intermittency. The Modern Era Retrospective-Analysis for Research and Applications (MERRA) boundary layer flux data has been used to construct wind profile at 50m, 80m, 100m and 120m turbine hub heights. The wind power density estimates at 50m are qualitatively similar to those in the US wind atlas developed by the National Renewable Energy Laboratory (NREL), but quantitatively a class less in some regions, but are within the limits of uncertainty. The wind speeds at 80m were quantitatively and qualitatively close to the NREL wind map. The possible reasons for overestimation by NREL have been discussed. For long tailed distributions like those of the wind power density, the mean is an overestimation and median is suggested for summary representation of the wind resource. The impact of raising the wind turbine hub height on metrics of abundance, persistence, variability and intermittency is analyzed. There is a general increase in availability and abundance of wind resource but the there is an increase in intermittency in terms of level crossing rate in low resource regions. The key aspect of geographical diversification of wind farms to mitigate intermittency - that the wind power generators are statistically independent - is also tested. This condition is found in low resource regions like the east and west coasts. However, in the central US region which has rich resource the condition fails as widespread coherent intermittence in wind power density is found. Thus large regions are synchronized in having wind power or lack thereof. Thus, geographical diversification in this region needs to be planned strategically. The annual distribution of hourly wind power density shows considerable variability and suggests wind floods and droughts that roughly correspond with La-Nina and El-Nino years respectively. The collective behavior of wind farms in seven Independent System Operator (ISO) areas has also been studied. The generation duration curves for each ISO show that there is no aggregated power for some fraction of the time. Aggregation of wind turbines mitigates intermittency to some extent, but each ISO has considerable fraction of time with less than 5% capacity. The hourly wind power time series show benefit of aggregation but the high and low wind events are lumped in time, thus corroborating the result that the intermittency is synchronized. The time series show that there are instances when there is no wind power in most ISOs because of large-scale high pressure systems. An analytical consideration of the collective behavior of aggregated wind turbines shows that the benefit of aggregation saturates beyond ten units. Also, the benefit of aggregation falls rapidly with temporal correlation between the generating units

Characterization of the Solar Power Resource in Europe and Assessing Benefits of Co-Location with Wind Power Installations

The extent, availability and reliability of solar power generation are assessed over Europe, and—following a previously developed methodology—special attention is given to the intermittency of solar power. Combined with estimates of wind power resource over Europe from a companion assessment, we assess the benefits of co-location of solar and wind power installations, particularly with respect to aggregate power generation and local mitigation of intermittency. Consistent with previous studies, our results show that the majority of solar potential is found in southern Europe, which also displays the strongest availability. We also found that higher latitude locations, around central Europe, benefit from medium to high solar power during the warm season. If a region’s availability of solar power is sufficient—as determined by a minimum technological threshold for photovoltaic extraction— it possesses the potential to reduce intermittency by aggregation and interconnection. We find these conditions occurring to a moderate extent over mainland central Europe. Finally, the result of co location of wind and solar power is increased power availability over the whole continent, especially in central Europe where neither resource is strong. In terms of local intermittency mitigation, the regions that benefit most are the Mediterranean and Baltic countries

Process Modeling of Global Soil Nitrous Oxide Emissions

http://globalchange.mit.edu/research/publications/2213Nitrous oxide is an important greenhouse gas and is a major ozone-depleting substance. To understand and quantify soil nitrous oxide emissions, we expanded the Community Land Model with prognostic Carbon and Nitrogen (CLM-CN) by inserting a module to estimate annually- and seasonally-varying nitrous oxide emissions between 1978 and 2000. We evaluate our soil N2O emission estimates against existing emissions inventories, other process-based model estimates, and observations from two forest sites in the Amazon and one in the United States. The model reproduces soil temperature and soil moisture relatively well, and it reconfirms the important relationship between N2O emissions and these parameters. The model also reproduces observations of N2O emissions well in the Amazonian forests but not during the winter in the USA. Applying this model to estimate the past 23 years of global soil N2O emissions, we find that there is a significant decrease in soil N2O emissions associated with drought and El Ni˜no years. More study is necessary to quantify the high-latitude winter activity in the model in order to better understand the impact of future climate on N2O emissions and vice versa.NASA Upper Atmosphere Research Program grants NNX11AF17G and NNX07AE89

Characterization of the Wind Power Resource in Europe and its Intermittency

Wind power is assessed over Europe, with special attention given to the quantification of intermittency. Using the methodology developed in Gunturu and Schlosser (2011), the MERRA boundary flux data was used to compute wind power density profiles over Europe. Besides of the analysis of capacity factor, other metrics are presented to further quantify the availability and reliability of this resource and the extent to which wind-power intermittency is coincident across Europe. The analyses find that, consistent with previous studies, the majority of European wind power resources are located offshore. The largest wind power resources at onshore locations are found to be over Iceland, the United Kingdom, and along the northern coastlines of continental Europe. Other isolated pockets of higher wind power are found over Spain and along the Mediterranean coast of France. Overall, the availability of onshore wind power is low and is highly intermittent, while offshore locations show a high degree of persistence. However, for the strongest onshore locations of wind power—primarily over northern coastlines as well as the United Kingdom and Iceland—the evidence indicates that intermittency can be reduced by aggregation and interconnection of wind-power installations.The authors gratefully acknowledge the financial support for this work provided by the MIT Joint Program on the Science and Policy of Global Change through a consortium of industrial sponsors and Federal grants, including U.S. Department of Energy grant DE-FG02-94ER61937. In addition, the authors would like to thank Mr. Hervé Le Treut and Prof. Ronald G. Prinn, who have given the opportunity to Alexandra Cosseron, French graduate student from Ecole Polytechnique and Ecole des Mines de Paris, to join the MIT Joint Program on the Science and Policy of Global Change for this work

Application of the Analogue Method to Modeling Heat Waves: A Case Study With Power Transformers

Large power transformers (LPTs) are critical yet increasingly vulnerable components of the power grid. More frequent and intense heat waves or high temperatures can degrade their operational lifetime and thereby increase the premature failure risk. Without adequate preparedness, a widespread situation would ultimately lead to prolonged grid disruption and incur excessive economic costs. In this study, we investigate the impact of climate warming and corresponding shifts in heat waves on a selected LPT located in the Northeast corridor of the United States. We apply an analogue method, which detects the occurrence of heat waves based on the salient, associated large-scale atmospheric conditions (“composites”), to assess the risk of future change in heat wave occurrence. Compared with the more conventional approach that relies on climate model-simulated daily maximum temperature, the analogue method produces model medians of late twentieth-century heat wave frequency that are more consistent with observation and have stronger inter-model consensus. Under the future climate warming scenarios, multi-model medians of both model daily maximum temperature and the analogue method indicate strong decadal increases in heat wave frequency by the end of the 21st century, but the analogue method improves model consensus considerably. We perform a preliminary assessment on the decrease of transformer lifetime with temperature increase. Future work will focus on using more advanced algorithms to quantify the impact of more frequent heat waves on the transformer’s expected lifetime and associated additional costs. The improved inter-model consensus of the analogue method is viewed as a promising step toward providing actionable information for a more stable, reliable, and environmentally responsible national grid.This work was funded by MIT Lincoln Lab (DE-FOA-0000768)

The Future Water Risks Under Global Change in Southern and Eastern Asia: Implications of Mitigation

Understanding and predicting the future vulnerability of freshwater resources is a major challenge with important societal implications. Many studies have identified Asia as a hotspot of severe water stress in the coming decades, and also highlighted the large uncertainty associated with water resource assessment based on limited multi-model projections. Here we provide a more comprehensive risk-based assessment of water use and availability in response to future climate change, socioeconomic growth, and their combination in Southern and Eastern Asia. We employ a large ensemble of scenarios that capture the spectrum of regional climate response as well as a range of economic projections and climate policies in a consistent, integrated modeling framework. We show that economic growth increases water stress ubiquitously. The climate-only and combined climate-growth effects on water stress remain largely negative in China and Indus Basin, but largely positive in India, Indochina, and Ganges Basin. However, climate poses substantially large uncertainty in water stress changes than socioeconomic growth. By 2050, socioeconomic growth alone can lead to an additional 650 million people living under at least “heavy” water stress, with most of these located in India, Indus Basin, and China. The combined effects of socioeconomic growth and climate change reduce people under water stress to an additional 200 million, attributed mainly to the beneficial climate in India that moves its heavily-stressed condition into the slightly or moderately‑stressed conditions. These 200 million people primarily reside in Indus Basin and China under at least overly exploited water conditions— where total water requirements will consistently exceed surface water supply. Climate mitigation helps alleviating the risks of increasing water scarcity by midcentury, but to a limited extent. Therefore, adaptive measures need to be taken to meet these surface water shortfalls, or a combination of both approaches may be most effective.This work was supported by the Department of Energy under An Integrated Framework for Climate Change Assessment (DE-FG02-94ER61937) and other government, industry and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change. For a complete list of sponsors and U.S. government funding sources, see http://globalchange.mit.edu/sponsors

CliCrop: a Crop Water-Stress and Irrigation Demand Model for an Integrated Global Assessment Model Approach

http://globalchange.mit.edu/research/publications/2264This paper describes the use of the CliCrop model in the context of climate change general assessment modeling. The MIT Integrated Global System Model (IGSM) framework is a global integrated assessment modeling framework that uses emission predictions and economic outputs from the MIT Emission Prediction and Policy Analysis (EPPA) model and earth system modeling predictions from the IGSM to drive a land system component, a crop model (CliCrop) and a Water Resource System (WRS) model. The global Agriculture and Water System are dependant upon and interlinked with the global climate system. As irrigated agriculture provides 60% of grains and 40% of all crop production on 20% of global crop lands and accounts for 80% of global water consumption, it is crucial that the agricultural-water linkage be properly modeled. Crop models are used to predict future yields, irrigation demand and to understand the effect of crop and soil type on food productivity and soil fertility. In the context of an integrated global assessment, a crop water-stress and irrigation demand model must meet certain specifications that are different for other crop models; it needs to be global, fast and generic with a minimal set of inputs. This paper describes how CliCrop models the physical and biological processes of crop growth and yield production and its use within the MIT Integrated Global System Model (IGSM) framework, including the data inputs. This paper discusses the global data bases used as input to CliCrop and provides a comparison of the accuracy of CliCrop with the detailed biological-based crop model DSSAT as well as with measured crop yields over the U.S. at the country level using reanalyzed weather data. In both cases CliCrop performed well and the analysis validated its use for climate change impact assessment. We then show why correctly modeling the soil is important for irrigation demand calculation, especially in temperate areas. Finally, we discuss a method to estimate actual water withdrawal from modeled physical crop requirements using U.S. historical data.The initial funding for CliCrop was provided by USAID under a program on climate change adaptation in Niger. Further funding was provided by UN University World Institute for Development Economics Research for the Application and Development of CliCrop in Africa, the authors would like to particularly thank Prof. Finn Tarp, Prof. Channing Arndt and Dr. James Thurlow for their support. The authors also would like to thank Dr. Jawoo Koo of IFPRI for his review and contributions to the software development. The authors also gratefully acknowledge additional financial support for this work provided by the MIT Joint Program on the Science and Policy of Global Change through a consortium of industrial sponsors and Federal grants. Development of the IGSM applied in this research was supported by the U.S. Department of Energy, Office of Science (DE-FG02-94ER61937); the U.S. Environmental Protection Agency, EPRI, and other U.S. government agencies and a consortium of 40 industrial and foundation sponsors

21st Century Changes in U.S. Heavy Precipitation Frequency Based on Resolved Atmospheric Patterns

Gridded precipitation-gauge observations and global atmospheric reanalysis are combined to develop an analogue method for detecting the occurrence of heavy precipitation events based on the prevailing large-scale atmospheric conditions. Combinations of different atmospheric variables for circulation features (geopotential height and wind vector) and moisture plumes (surface specific humidity, column precipitable water, and precipitable water up to 500hPa) are examined to construct the analogue schemes for the winter (DJF) of the Pacific Coast California (PCCA) and the summer (JJA) of the Midwestern United States (MWST). The detection diagnostics of various analogue schemes are calibrated with 27-yr (1979–2005) and then validated with 9-yr (2006–2014) NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA). All of the analogue schemes are found to significantly improve upon MERRA precipitation in characterizing the number and interannual variations of observed heavy precipitation events in the MWST which is one of weakest regions for MERRA summer precipitation. When evaluated with the late 20th century simulations from an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), all analogue schemes produce model medians of heavy precipitation frequency that are more consistent with observations and have smaller inter-model discrepancies when compared with the model-based precipitation. Further, the performances of analogue schemes with vector winds are comparable to those of geopotential height, and no analogue scheme with one of three water vapor content variables is clearly superior to another. Under two radiative forcing scenarios (Representative Concentration Pathways 4.5 and 8.5), the CMIP5-based analogue schemes produce a trend in the occurrence of heavy events through the 21st century consistent with the model-based precipitation, but with smaller inter-model disparity. The strongest reduction in the disparity of the results is seen for the RCP8.5 scenario. The median trends in DJF heavy precipitation frequency for PCCA are positive, but for JJA heavy event frequency over the MWST region, the median trends are slightly negative. Overall, the presented analyses highlight the potential of the analogue as a powerful diagnostic tool for model deficiencies and its complementarity to an evaluation that considers modeled precipitation alone to assess heavy precipitation frequency. The consistency found here between projections from analogues and model precipitation increases confidence in projected heavy precipitation frequency changes in a warming climate.This work was funded by the NASA Energy and Water Cycle Study Research Announcement (NNH07ZDA001N) and MacroSystems Biology Program Grant (NSF-AES EF#1137306) from the National Science Foundation

A Framework for Analysis of the Uncertainty of Socioeconomic Growth and Climate Change on the Risk of Water Stress: a Case Study in Asia

The sustainability of future water resources is of paramount importance and is affected by many factors, including population, wealth and climate. Inherent in how these factors change in the future is the uncertainty of their prediction. In this study, we integrate a large ensemble of scenarios—internally consistent across economics, emissions, climate, and population—to develop a risk portfolio of water stress over a large portion of Asia that includes China, India, and Mainland Southeast Asia. We isolate the effects of socioeconomic growth from the effects of climate change in order to identify the primary drivers of stress on water resources. We find that water needs related to socioeconomic changes, which are currently small, are likely to increase considerably in the future, often overshadowing the effect of climate change on levels of water stress. As a result, there is a high risk of severe water stress in densely populated watersheds by 2050, compared to recent history. If socio-economic growth is unconstrained by global actions to limit greenhouse gas concentrations, water-stressed populations may increase from about 800 million to 1.7 billion in this region.The Joint Program on the Science and Policy of Global Change is funded by a consortium of industrial and foundation sponsors. For the complete list see http://globalchange.mit.edu/sponsors/all

Conditional quantum logic using two atomic qubits

In this paper we propose and analyze a feasible scheme where the detection of a single scattered photon from two trapped atoms or ions performs a conditional unitary operation on two qubits. As examples we consider the preparation of all four Bell states, the reverse operation that is a Bell measurement, and a CNOT gate. We study the effect of atomic motion and multiple scattering, by evaluating Bell inequalities violations, and by calculating the CNOT gate fidelity.Comment: 23 pages, 8 figures in 11 file