# Renewable Electric Power and Grid Integration

In Press
Changyi Liu, Yang Wang, and Rong Zhu. In Press. “Assessment of the economic potential of China's onshore wind electricity.” Resources, Conservation and Recycling. Publisher's Version Abstract

The assessment of the economic potential of wind electricity is of critical importance for wind power development in China. Based on the wind resource data between 1995 and 2014 and geological assumptions, this paper calculates economic potential of China’s onshore wind electricity. Furthermore, it builds an econometric model to update the net-present-value model, based on a survey sample of various wind farms. Results show that the economic potential of China’s onshore wind electricity is 8.13 PWh per year with a feed-in-tariff price at 0.60 yuan (about 9.6 U.S. cents) per kilowatt-hour.

Xi Lu and Michael B. McElroy. In Press. “Global potential for wind generated electricity.” In Wind Energy Engineering: A Handbook for Onshore and Offshore Wind Turbines, edited by Trevor M. Letcher. Amsterdam: Elsevier.
Submitted
Xingning Han, Xinyu Chen, Michael B. McElroy, Shiwu Liao, Chris P. Nielsen, and Jinyu Wen. Submitted. “Fast unit commitment for power system planning under high penetration of variable renewables.” IEEE Transactions on Power Systems.
Xinyu Chen, Michael B. McElroy, and Chongqing Kang. Submitted. “Integrated energy systems for higher wind penetration in China: Formulation, implementation, and impacts.” IEEE Transactions on Power Systems.
Xinyu Chen, Zhiwei Xu, Chris P Nielsen, and Michael B. McElroy. Submitted. “Plug-in electric vehicles: Opportunities to reduce emissions of CO2 and conventional pollutants in China.” Nature Energy.
X.D. Wu, Q. Yang, G.Q. Chen, T. Hayat, and A. Alsaedi. Submitted. “Progress and prospect of CCS in China: Using learning curve to assess the cost-viability of a 2x600 MW retrofitted oxyfuel power plant as a case study.” Renewable and Sustainable Energy Reviews.
Peter Sherman, Xinyu Chen, and Michael B. McElroy. Submitted. “Variations of wind potential for China and Mongolia associated with changing global climate and natural oscillations.” Proceedings of the National Academy of Sciences.
2017
Michael B. McElroy and Xinyu Chen. 2017. “Wind and solar power in the United States: Status and prospects.” CSEE Journal of Power and Energy Systems, 1, 3. Abstract

The United States has committed to reduce its greenhouse gas emissions by 26%–28% by 2025 and by 83% by 2050 relative to 2005. Meeting these objectives will require major investments in renewable energy options, particularly wind and solar. These investments are promoted at the federal level by a variety of tax credits, and at the state level by requirements for utilities to include specific fractions of renewable energy in their portfolios (Renewable Portfolio Standards) and by opportunities for rooftop PV systems to transfer excess power to utilities through net metering, allowing meters to operate in reverse. The paper discusses the current status of these incentives.

2016
Xi Lu, Michael B. McElroy, Wei Peng, Shiyang Liu, Chris P. Nielsen, and Haikun Wang. 2016. “Challenges faced by China compared with the US in developing wind power.” Nature Energy, 6, 1. Publisher's Version Abstract

In the 21st Conference of the Parties to the UNFCCC held in Paris in December 2015, China pledged to peak its carbon emissions and increase non-fossil energy to 20% by 2030 or earlier. Expanding renewable capacity, especially wind power, is a central strategy to achieve these climate goals. Despite greater capacity for wind installation in China compared to the US (145.1 versus 75.0 GW), less wind electricity is generated in China (186.3 versus 190.9 TWh). Here, we quantify the relative importance of the key factors accounting for the unsatisfactory performance of Chinese wind farms. Different from the results in earlier qualitative studies, we find that the difference in wind resources explains only a small fraction of the present China-US difference in wind power output (17.9% in 2012); the curtailment of wind power, differences in turbine quality, and delayed connection to the grid are identified as the three primary factors (respectively 49.3%, 50.2%, and 50.3% in 2012). Improvements in both technology choices and the policy environment are critical in addressing these challenges.

Qing Yang, Yingquan Chen, Haiping Yang, and Hanping Chen. 2016. “Greenhouse gas emissions of a biomass-based pyrolysis plant in China.” Renewable and Sustainable Energy Reviews, January, 53: 1580-1590. Publisher's Version Abstract

Biomass pyrolysis offers an alternative to industrial coal-fired boilers and utilizes low temperature and long residence time to produce syngas, bio-oil and biochar. Construction of biomass-based pyrolysis plants has recently been on the rise in rural China necessitating research into the greenhouse gas emission levels produced as a result. Greenhouse gas emission intensity of a typical biomass fixed-bed pyrolysis plant in China is calculated as 1.55E−02 kg CO2-eq/MJ. Carbon cycle of the whole process was investigated and found that if 41.02% of the biochar returns to the field, net greenhouse gas emission is zero indicating the whole carbon cycle may be renewable. A biomass pyrolysis scenario analysis was also conducted to assess exhaust production, transportation distance and the electricity-generation structure for background information applied in the formulation of national policy.

Meiyu Guo, Xi Lu, Chris P. Nielsen, Michael B. McElroy, Wenrui Shi, Yuntian Chen, and Xuan Yu. 2016. “Prospects for shale gas production in China: Implications for water demand.” Renewable and Sustainable Energy Reviews, December, 66: 742-750. Publisher's Version Abstract

Development of shale gas resources is expected to play an important role in China's projected transition to a low-carbon energy future. The question arises whether the availability of water could limit this development. The paper considers a range of scenarios to define the demand for water needed to accommodate China's projected shale gas production through 2020. Based on data from the gas field at Fuling, the first large-scale shale gas field in China, it is concluded that the water intensity for shale gas development in China (water demand per unit lateral length) is likely to exceed that in the US by about 50%. Fuling field would require a total of 39.9–132.9 Mm3 of water to achieve full development of its shale gas, with well spacing assumed to vary between 300 and 1000 m. To achieve the 2020 production goal set by Sinopec, the key Chinese developer, water consumption is projected to peak at 7.22 Mm3 in 2018. Maximum water consumption would account for 1% and 3%, respectively, of the available water resource and annual water use in the Fuling district. To achieve China's nationwide shale gas production goal set for 2020, water consumption is projected to peak at 15.03 Mm3 in 2019 in a high-use scenario. It is concluded that supplies of water are adequate to meet demand in Fuling and most projected shale plays in China, with the exception of localized regions in the Tarim and Jungger Basins.

Ning Zhang, Xi Lu, Chris P Nielsen, Michael B. McElroy, Xinyu Chen, Yu Deng, and Chongqing Kang. 2016. “Reducing curtailment of wind electricity in China by employing electric boilers for heat and pumped hydro for energy storage.” Applied Energy, 184: 987-994. Publisher's Version Abstract

Accommodating variable wind power poses a critical challenge for electric power systems that are heavily dependent on combined heat and power (CHP) plants, as is the case for north China. An improved unit-commitment model is applied to evaluate potential benefits from pumped hydro storage (PHS) and electric boilers (EBs) in West Inner Mongolia (WIM), where CHP capacity is projected to increase to 33.8 GW by 2020. A business-as-usual (BAU) reference case assumes deployment of 20 GW of wind capacity. Compared to BAU, expanding wind capacity to 40 GW would allow for a reduction in CO2 emissions of 33.9 million tons, but at a relatively high cost of US$25.3/ton, reflecting primarily high associated curtailment of wind electricity (20.4%). A number of scenarios adding PHS and/or EBs combined with higher levels of wind capacity are evaluated. The best case indicates that a combination of PHS (3.6 GW) and EBs (6.2 GW) together with 40 GW of wind capacity would reduce CO2 emissions by 43.5 million tons compared to BAU, and at a lower cost of US$16.0/ton. Achieving this outcome will require a price-incentive policy designed to ensure the profitability of both PHS and EB facilities.

2015
Junling Huang and Michael B. McElroy. 2015. “A 32-year perspective on the origin of wind energy in a warming climate.” Renewable Energy, May, 77: 482-492. Publisher's Version Abstract

Based on assimilated meteorological data for the period January 1979 to December 2010, the origin of wind energy is investigated from both mechanical and thermodynamic perspectives, with special focus on the spatial distribution of sources, historical long term variations and the efficiency for kinetic energy production. The dry air component of the atmosphere acts as a thermal engine, absorbing heat at higher temperatures, approximately 256 K, releasing heat at lower temperatures, approximately 252 K. The process is responsible for production of wind kinetic energy at a rate of 2.46 W/m2  sustaining thus the circulation of the atmosphere against frictional dissipation. The results indicate an upward trend in kinetic energy production over the past 32 years, indicating that wind energy resources may be varying in the current warming climate. This analysis provides an analytical framework that can be adopted for future studies addressing the ultimate wind energy potential and the possible perturbations to the atmospheric circulation that could arise as a result of significant exploitation of wind energy.

Yanxia Zhang, Haikun Wang, Sai Liang, Ming Xu, Qiang Zhang, Hongyan Zhao, and Jun Bi. 2015. “A dual strategy for controlling energy consumption and air pollution in China's metropolis of Beijing.” Energy, 1 March, 81: 294-303. Publisher's Version Abstract

It is critical to alleviate problems of energy and air pollutant emissions in a metropolis because these areas serve as economic engines and have large and dense populations. Drivers of fossil fuel use and air pollutants emissions were analyzed in the metropolis of Beijing during 1997-2010. The analyses were conducted from both a bottom-up and a top-down perspective based on the sectoral inventories and structural decomposition analysis (SDA). From a bottom-up perspective, the key energy-intensive industrial sectors directly caused the variations in Beijing's air pollution by means of a series of energy and economic policies. From a top-down perspective, variations in production structures caused increases in most materials during 2000-2010, but there were decreases in PM10 and PM2.5 emissions during 2005-2010. Population growth was found to be the largest driver of energy consumption and air pollutant emissions during 1997-2010. This finding suggests that avoiding rapid population growth in Beijing could simultaneously control energy consumption and air pollutant emissions. Mitigation policies should consider not only the key industrial sectors but also socioeconomic drivers to co-reduce energy consumption and air pollution in China's metropolis.

2014
Junling Huang. 2014. “A climate-friendly energy future: Prospects for wind.” School of Engineering and Applied Sciences, Harvard University.
Junling Huang, Xi Lu, and Michael B. McElroy. 2014. “Meteorologically defined limits to reduction in the variability of outputs from a coupled wind farm system in the Central US.” Renewable Energy, February, 62: 331–340. Publisher's Version Abstract

Studies suggest that onshore wind resources in the contiguous US could readily accommodate present and anticipated future US demand for electricity. The problem with the output from a single wind farm located in any particular region is that it is variable on time scales ranging from minutes to days posing difficulties for incorporating relevant outputs into an integrated power system. The high frequency (shorter than once per day) variability of contributions from individual wind farms is determined mainly by locally generated small-scale boundary layer. The low frequency variability (longer than once per day) is associated with the passage of transient waves in the atmosphere with a characteristic time scale of several days. Using 5 years of assimilated wind data, we show that the high frequency variability of wind-generated power can be significantly reduced by coupling outputs from 5 to 10 wind farms distributed uniformly over a ten state region of the Central US in this study. More than 95% of the remaining variability of the coupled system is concentrated at time scales longer than a day, allowing operators to take advantage of multi-day weather forecasts in scheduling projected contributions from wind.

Xi Lu, Michael B. McElroy, Xinyu Chen, and Chongqing Kang. 2014. “Opportunity for offshore wind to reduce future demand for coal-fired power plants in China with consequent savings in emissions of CO2.” Environmental Science & Technology, 24, 48: 14764–14771. Publisher's Version Abstract

Although capacity credits for wind power have been embodied in power systems in the U.S. and Europe, the current planning framework for electricity in China continues to treat wind power as a non-dispatchable source with zero contribution to firm capacity. This study adopts a rigorous reliability model for the electric power system evaluating capacity credits that should be recognized for offshore wind resources supplying power demands for Jiangsu, China. Jiangsu is an economic hub located in the Yangtze River delta accounting for 10% of the total electricity consumed in China. Demand for electricity in Jiangsu is projected to increase from 331 TWh in 2009 to 800 TWh by 2030. Given a wind penetration level of 60% for the future additional Jiangsu power supply, wind resources distributed along the offshore region of five coastal provinces in China (Shandong, Jiangsu, Shanghai, Zhejiang and Fujian) should merit a capacity credit of 12.9%, the fraction of installed wind capacity that should be recognized to displace coal-fired systems without violating the reliability standard. In the high-coal-price scenario, with 60% wind penetration, reductions in CO2 emissions relative to a business as usual reference could be as large as 200.2 million tons of CO2 or 51.8% of the potential addition, with a cost for emissions avoided of $29.0 per ton. Xinyu Chen, Xi Lu, Michael B. McElroy, Chris P Nielsen, and Chongqing Kang. 2014. “Synergies of wind power and electrified space heating: A case study for Beijing.” Environmental Science & Technology, 3, 48: 2016–2024. Publisher's Version Abstract Demands for electricity and energy to supply heat are expected to expand by 71% and 47%, respectively, for Beijing in 2020 relative to 2009. If the additional electricity and heat are supplied solely by coal as is the current situation, annual emissions of CO2 may be expected to increase by 59.6% or 99 million tons over this interval. Assessed against this business as usual (BAU) background, the present study indicates that significant reductions in emissions could be realized using wind-generated electricity to provide a source of heat, employed either with heat pumps or with electric thermal storage (ETS) devices. Relative to BAU, reductions in CO2 with heat pumps assuming 20% wind penetration could be as large as 48.5% and could be obtained at a cost for abatement of as little as$15.6 per ton of avoided CO2. Even greater reductions, 64.5%, could be realized at a wind penetration level of 40% but at a higher cost, \$29.4 per ton. Costs for reduction of CO2 using ETS systems are significantly higher, reflecting the relatively low efficiency for conversion of coal to power to heat.

2013
Xi Lu, Michael B. McElroy, Chris P Nielsen, Xinyu Chen, and Junling Huang. 2013. “Optimal integration of offshore wind power for a steadier, environmentally friendlier, supply of electricity in China.” Energy Policy, 62: 131–138. Publisher's Version Abstract

Demand for electricity in China is concentrated to a significant extent in its coastal provinces. Opportunities for production of electricity by on-shore wind facilities are greatest, however, in the north and west of the country. Using high resolution wind data derived from the GEOS-5 assimilation, this study shows that investments in off-shore wind facilities in these spatially separated regions (Bohai-Bay or BHB, Yangtze-River Delta or YRD, Pearl-River Delta or PRD) could make an important contribution to overall regional demand for electricity in coastal China. An optimization analysis indicates that hour-to-hour variability of outputs from a combined system can be minimized by investing 24% of the power capacity in BHB, 30% in YRD and 47% in PRD. The analysis suggests that about 28% of the overall off-shore wind potential could be deployed as base load power replacing coal-fired system with benefits not only in terms of reductions in CO2 emissions but also in terms of improvements in regional air quality. The interconnection of off-shore wind resources contemplated here could be facilitated by China's 12th-five-year plan to strengthen inter-connections between regional electric-power grids.

2012
Xi Lu, Michael B. McElroy, Gang Wu, and Chris P Nielsen. 2012. “Accelerated reduction of SO2 emissions from the US power sector triggered by changing prices of natural gas.” Environmental Science and Technology, 14, 46: 7882-7889. Click here for the article on the journal webpage.