Lu, Xi

China is now the largest emitter of CO₂ in the world, having contributed nearly half of the global increase in carbon emissions between 1980 and 2010. The existing literature on China’s carbon emissions has focused on two dimensions: the amount of CO₂ emitted within China’s geographical boundaries (a production-based perspective), and the drivers of, and responsibility for, these emissions (a consumption-based perspective). The current study begins with a comprehensive review of China’s CO₂ emissions, and then analyzes their driving forces from both consumption and production perspectives, at both national and provincial levels. It is concluded that China’s aggregate national CO₂ emissions from fossil fuel consumption and cement production maintained high growth rates during 2000-2010. National emissions reached 6.8–7.3 billion tons in 2007, nearly 25% of which were caused by net exports (i.e., exports minus imports) to other countries. However, emission characteristics varied significantly among different regions and provinces, and considerable emission leakage from the developed eastern regions to inland and western areas of the country was found. The objectives of China’s policies should therefore be broadened from continued improvement of energy efficiency to accelerating regional technology transfer and preventing mere relocation of carbon-intensive economic activities from developed coastal regions to less developed, inland provinces. To rapidly and effectively cut down China’s carbon emissions, moreover, its energy supply should be aggressively decarbonized by promoting renewable and low carbon energy sources.

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.

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.

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.

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.

Wind power accounted for 42% of all new electrical capacity added to the United States electrical system in 2008 although wind continues to account for a relatively small fraction of the total electricity-generating capacity [25.4 gigawatts (GW) of a total of 1,075 GW] (ref. 1; www.awea.org/pubs/documents/Outlook_2009.pdf). The Global Wind Energy Council projected the possibility of a 17-fold increase in wind-powered generation of electricity globally by 2030 (ref. 2; www.gwec.net/fileadmin/documents/Publications/GWEO_2008_final.pdf). Short et al. (3), using the National Renewable Energy Laboratory's WinDs model, concluded that wind could account for as much as 25% of U.S. electricity by 2050 (corresponding to an installed wind capacity of ≈300 GW).

Archer and Jacobson (4) estimated that 20% of the global total wind power potential could account for as much as 123 petawatt-hours (PWh) of electricity annually [corresponding to annually averaged power production of 14 terawatts (TW)] equal to 7 times the total current global consumption of electricity (comparable to present global use of energy in all forms). Their study was based on an analysis of data for the year 2000 from 7,753 surface meteorological stations complemented by data from 446 stations for which vertical soundings were available. They restricted their attention to power that could be generated by using a network of 1.5-megawatt (MW) turbines tapping wind resources from regions with annually averaged wind speeds in excess of 6.9 m/s (wind class 3 or better) at an elevation of 80 m. The meteorological stations used in their analysis were heavily concentrated in the United States, Europe, and Southeastern Asia. Results inferred for other regions of the world are subject as a consequence to considerable uncertainty.

The present study is based on a simulation of global wind fields from version 5 of the Goddard Earth Observing System Data Assimilation System (GEOS-5 DAS). Winds included in this compilation were obtained by retrospective analysis of global meteorological data using a state-of-the-art weather/climate model incorporating inputs from a wide variety of observational sources (5), including not only surface and sounding measurements as used by Archer and Jacobson (4) but also results from a diverse suite of measurements and observations from a combination of aircraft, balloons, ships, buoys, dropsondes and satellites, in short the gamut of observational data used to provide the world with the best possible meteorological forecasts enhanced by application of these data in a retrospective analysis. The GEOS-5 wind field is currently available for the period 2004 to the present (March 20, 2009) with plans to extend the analysis 30 years back in time. The GEOS-5 assimilation was adopted in the present analysis to take advantage of the relatively high spatial resolution available with this product as compared with the lower spatial resolutions available with alternative products such as ERA-40, NECP II, and JRA-25. It is used here in a detailed study of the potential for globally distributed wind-generated electricity in 2006.

We begin with a description of the methodology adopted for the present study. The land-based turbines envisaged here are assumed to have a rated capacity of 2.5 MW with somewhat larger turbines, 3.6 MW, deployed offshore, reflecting the greater cost of construction and the economic incentive to deploy larger turbines to capture the higher wind speeds available in these regions. In siting turbines over land, we specifically excluded densely populated regions and areas occupied by forests and environments distinguished by permanent snow and ice cover (notably Greenland and Antarctica). Turbines located offshore were restricted to water depths <200 m and to distances within 92.6 km (50 nautical miles) of shore.

These constraints are then discussed, and results from the global analysis are presented followed by a more detailed discussion of results for the United States.