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Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

2
Resource Base

Both the United States and China have significant renewable energy resources. In this chapter, the committees describe the more developed non-hydro resources—wind, solar, and biomass—that could contribute significantly to the electricity supply in both nations. This is followed by summaries of the geothermal and hydrokinetic energy sources under development in the United States that may have applicability in China. China is at a comparatively early stage of assessing its renewable resources for power production, and so the balance of the chapter presents additional information on what has been done in the United States, which should be instructive as China improves its own capacity in this field.

ASSESSING RENEWABLE RESOURCES

Assessing the quality and quantity of renewable resources is a complex but necessary step in determining the potential of a particular resource. The question of potential has multiple answers depending on whether an assessment measures the technical, economic, or regional characteristics of a resource.

Theoretical potential is the upper boundary of the assessed value. For instance Lu et al. (2009) estimated theoretical wind energy potentials for the United States and China to be 320 exajoules1 (EJ) and 160 EJ, respectively.

Technical potential is expressed as an inventory of a resource that could be developed by any and all appropriate conversion technologies without regard to cost. An assessment of technical potential takes into consideration geographic

1

An SI unit of energy equals 1018 joules.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

restrictions (e.g., terrain, weather, environmental conditions, ecological limitations, cultural issues, etc.). As technologies and methodologies for defining the technical potential of a renewable resource improve over time, uncertainties in assessments are reduced and confidence in the results increases.

Economic potential is expressed as a supply curve showing the quantity of a resource available at a specific cost. Methodologies for calculating the economic potential of a renewable resource have variable degrees of complexity by source and include considerations of energy, environmental, economic, existing and new infrastructure, and social factors.2 When sustainability factors are included, economic potentials can be refined into a “sustainable potential” for a specific region. Sustainability factors can be local, national, or international (e.g., changes in land use caused directly or indirectly by the expansion of energy or other economic activity [see Chapter 4]).

Regional potential assessments include the potential of multiple resources in a geographic area (multiple inventories in a certain region). A regional potential assessment can be combined with geographic information of the existing infrastructure (e.g., conventional electricity generation and transmission) and economic information to support integrated resource planning and development for policy makers, industry, and project developers. As costs for renewable energy technologies come down, regions with lower quality wind and solar resources may be able to reassess their economic potential.

Most renewable electricity generation must be located near the source of the renewable energy flux (i.e., the rate of energy transfer through a unit area). This means that even if a source does not contribute significantly to total (national) electricity generation, it could still provide a substantial contribution to regional power generation (NAS/NAE/NRC, 2010a). Biomass, for example, can be stored and made available to meet specific demand, although there are limitations to this, including the distance the biomass can be economically transported and the ability of the power generation technologies to cycle on or off (i.e., to meet peak or intermittent demand).

In the following sections, advances in quantitative characterizations of wind, solar, and biomass, with examples of technical and economic potentials, are highlighted. Some information on geothermal and hydrokinetic energy is also provided. Table 1-1 from the previous chapter can be used as a reference point in drawing comparisons to present installed capacity (in GW) and electrical generation (in terawatt hours [TWh]) in the United States and China.

2

The Intergovernmental Panel on Climate Change defines economic potential as: “The portion of the technical potential for GHG emissions reductions or energy-efficiency improvements that could be achieved cost-effectively in the absence of market barriers. The achievement of the economic potential requires additional policies and measures to break down market barriers.” Available online at http://www.gcrio.org/ipcc/techrepI/appendixe.html.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-1 Contiguous U.S. Windy Land Characterization and Wind Energy Technical Potential for Wind Classes ≥ 3 and Gross Capacity Factors ≥ 30 Percent (without losses)

Windy Land Characterization

 

Key Variables

Wind Energy Technical Potential

 

Reference

Total million km2

Excluded million km2

Available million km2

Hub height m

Spatial resolution km

Installed capacity at 5 MW/km2 GW

Annual generation million GWh

EJ

 

2.57

 

1.04

50

5 × 5

5,200

11.4

40

Elliott et al., 1991

2.57

 

 

80

0.2 × 0.2 to 5 × 5

7,000–8,000

15–20

50–60

Elliott et al., 2010

2.57

0.47

2.10

80

0.2 × 0.2

10,500

36.9

135

AWS Truewind, LLC and NREL, 2010

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

WIND POWER IN THE UNITED STATES

In a seminal work by Elliott et al. (1991), the total estimated electricity technical potential of wind in the continental United States was 11 million gigawatt hours per year (GWh/yr) from regions with winds rated as Class 3 or higher3 and a turbine hub height of 50 meters (m). In energy units, 11 million GWh represents 40 exajoules (EJ), or approximately 40 percent of primary energy demand for 2007. By 2010, as a result of advances in wind turbine technology, the characterization and use of windy lands, and increased hub heights, the technical potential improved significantly. As Table 2-1 shows, technological improvements, a 25-fold increase in spatial resolution (from 5.0 × 5.0 kilometers [km] down to 0.2 × 0.2 km), and an 80 m hub height tripled the technical potential to 37 million GWh, or 135 EJ of energy. Figure 2-1 shows the significant changes in technical wind resource potential with changes in turbine hub height for the state of Indiana; hub height was raised from 50 to 100 m, which increased wind-speed intensities in a large portion of the state.

Extractable Potential

Continent-scale simulations indicate that high levels of wind power extraction could affect the geographic distribution and/or the inter- and intra-annual variability of winds, or might even alter the external conditions for wind development and climate conditions. Thus, model calculations suggest that, in addition to limiting the efficiency of large-scale wind farms, the extraction of wind energy from very large wind farms could have a measurable effect on weather and climate at the local, or even continental and global scales (Keith et al., 2004; Roy et al., 2004).

However, it is important to keep in mind that empirical and dynamical down-scaling modeling results vary greatly (Pryor et al., 2005, 2006). Large-scale wind modeling is a nascent field of research, and global and regional climate models (GCMs and RCMs) do not fully reproduce historical trends (Pryor et al., 2009). Recent analyses (e.g., Kirk-Davidoff and Keith, 2008; Barrie and Kirk-Davidoff, 2010) have suggested that higher vertical resolution would improve modeling results, by allowing for more analysis of large-scale wind farms as elevated momentum sinks, rather than surface roughness anomalies.

Several studies (e.g., Pryor et al., 2005, 2006) suggest that mean wind speeds and energy density over North America will remain within the range of inter-annual variability (i.e., ~15 percent) for the next century, but we will need more detailed, meso-scale models and measurements to determine total U.S. extractable wind energy potential and how much of that potential can be extracted without causing significant environmental impacts. Models are also being developed

3

Wind class, a measure of wind power density, is measured in watts per square meter and is a function of wind speed at a specific height from the ground.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-1 Comparison of the wind energy resource at 50 m, 70 m, and 100 m for the state of Indiana, United States. Source: DOE, 2008c.

FIGURE 2-1 Comparison of the wind energy resource at 50 m, 70 m, and 100 m for the state of Indiana, United States. Source: DOE, 2008c.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

to determine the optimal distance between wind farms to minimize power loss (Frandsen et al., 2007).

Assuming an estimated upper limit of 20 percent extraction of the energy in a wind field both regionally and on a continental scale and a total U.S. onshore wind electricity value of 11 million GWh/yr, an upper value estimate for the extractable wind-generated electricity potential would be about 2.2 million GWh/yr, more than half the electricity generated in the United States in 2007 (NAS/NAE/NRC, 2010a).

However, based on the 2010 estimates of technical potential, the extractable potential would be 7 million GWh/yr using only Class 3 and higher wind-speed areas in the contiguous United States (AWS Wind, LLC and NREL, 2010). This level of electricity generation would surpass the 5.8 million GWh/yr electricity demand projected for 2030 by the U.S. Energy Information Administration (EIA, 2007a). To reach the extractable potential (using only onshore wind resources) would require using an average of 5 percent of the contiguous land area of the United States, although the physical footprint of the turbines themselves would occupy a small fraction (< 5 percent) of this land area. This estimate, excludes protected lands (national parks, wilderness, etc.), incompatible land-use areas (urban areas, airports, wetlands, and water features), and other locations, which have a combined total of about 17 percent of the continental United States (AWS Wind, LLC and NREL, 2010).

Economic Potential

To estimate supply curves, scenarios can be formulated for a specific level of renewable resource penetration at a future time using a combination of models that take into account the following factors: the resource inventory; future deployment of renewable electricity products, including manufacture, installation, and operations; required capital investments and economic development in the presence (or absence) of specific policies; integration of renewable electricity into existing production, distribution, and end-use systems and required infrastructure changes; and market penetration. Production costs would be projected based on learning curves for specific generation technologies.

Comparing the overall costs of this renewable scenario with a baseline scenario with no renewable electricity penetration (e.g., using net present value) provides valuable information for governments, industries, and other organizations involved in developing investment strategies in renewable resources and policy decisions that take into account social and private costs and benefits. As the full discussion of the methodologies involved with the evidentiary basis for the development of economic potentials are described in Chapter 7 of the Electricity from Renewable Resources: Status, Prospects, and Impediments report (NAS/NAE/NRC, 2010a), this report will illustrate results for selected renewable technologies.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

One estimate of the economic potential of wind energy resources was made by the U.S. Department of Energy (DOE), two national laboratories (primarily the National Renewable Energy Laboratory [NREL] and Lawrence Berkeley National Laboratory [LBL]), the American Wind Energy Association, Black and Veatch Engineering and Consulting, and collaborators. The modeled scenario, “20 percent by 2030,” indicated a goal of 20 percent wind energy market penetration by 2030 in the United States (DOE, 2008a) and estimated costs of electricity to provide 1.2 million GWh/yr, or 20 percent of projected U.S. electricity generation (EIA, 2007a). The estimate took into account the challenges and needs in the areas of technology, manufacturing and employment, transmission and grid integration, markets, siting strategies, and potential environmental effects to reach this level of penetration.

The data analysis and model runs described in the report, which were based on 2006 data, concluded in mid-2007. In this first effort, no sensitivity analyses were performed. The technical potential modeled from these studies was better than 8,000 GW (in terms of installed capacity), a number that falls between the two estimates in Table 2-1, as expected, because the resource data resolution was 1 km × 1 km, and, in some cases 5 km × 5 km.

Figure 2-2 shows the “20 percent by 2030” estimated supply curve (economic potential) for onshore and offshore wind energy in the United States based on the 2007 model. The onshore lowest cost electricity comes from wind Classes 5 to 7 and supplies the first 50 GW of installed capacity. Classes 3 and 4 resources add an additional 750 GW at increasingly higher costs. Using wind turbines at 50 m hub height to generate 1.1 million GWh/yr was projected to require 300 GW of installed capacity. The affordable-to-harness installed capacity (economic potential) of land-based wind energy in this scenario was 800 GW.

The actual footprint of land-based turbines and related infrastructure in this model was estimated at about 1,000 to 2,500 km2 of dedicated land (an area about the size of Rhode Island). Thus, the turbines and associated infrastructure would physically occupy only 2 to 5 percent of the land being used for projects, meaning that some agricultural land could be used to produce energy as well as crops and rangeland products.

Critical assumptions in this scenario included a 35 percent reduction in operations and maintenance costs (to mitigate investment risk) and the extensions of incentives (e.g., production tax credits) to maintain investors’ confidence. The transmission system was estimated to require 19,000 miles of additional line to support about 300 GW of additional variable-output capacity. The plausible, high-voltage distribution system shown on Figure 2-3 is part of the significant infrastructure development that would be required over a period of 20 years.

Offshore Wind Energy Capacity

The available offshore wind capacity in the United States was initially estimated at 907 GW for distances of 5 to 50 nautical miles offshore (Musial and

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-2 Modeled economic potential of wind resources in the United States shown as a supply curve in which energy costs include connection to 10 percent of existing transmission grid capacity within 500 miles of the resource. Production tax credits are not included. Source: DOE, 2008a.

FIGURE 2-2 Modeled economic potential of wind resources in the United States shown as a supply curve in which energy costs include connection to 10 percent of existing transmission grid capacity within 500 miles of the resource. Production tax credits are not included. Source: DOE, 2008a.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-3 A concept of transmission with one technically feasible transmission grid of 765 kV overlayed on wind resource data combining low- and high-resolution datasets used to model the 20 percent wind scenario using NREL’s Regional Energy Deployment System (ReEDS)

FIGURE 2-3 A concept of transmission with one technically feasible transmission grid of 765 kV overlayed on wind resource data combining low- and high-resolution datasets used to model the 20 percent wind scenario using NREL’s Regional Energy Deployment System (ReEDS)

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

Butterfield, 2004). The depth of the water at these locations varies from about 30 to more than 900 m (NAS/NAE/NRC, 2010a). Schwartz et al. (2010) point out that this was a conservative assumption, excluding many regions (e.g., within 5 nautical miles of coastline) that subsequent analyses now include. More recent data from the “20 percent by 2030” scenario projects a technical potential, including shallow- and deep-water generation, of about 4,000 GW, or half the technical potential from the land-based, contiguous United States (AWS Wind LLC and NREL, 2010). The modeled economic potential in Figure 2-2 shows an overlap between offshore and onshore supply curves of about 50 GW.

Combined Onshore and Offshore Wind Resources

The “20 percent by 2030” scenario included 50 GW offshore and 250 GW onshore wind resources to provide 1.2 million GWh/yr, reductions in capital costs of 10 percent over the next two decades, and capacity increases of about 15 percent (corresponding to a 15 percent increase in annual energy generation by each wind plant). These optimistic assumptions were offset, at least partly, by higher technical potentials and additional resources that could become available at a hub height of >80 m, which would increase the low-cost supply of energy and expand its projected economic potential.

Modeling efforts will have to be expanded to include multiple scenarios and new data, improve and validate sub-models, and perform sensitivity and uncertainty analyses (using Monte Carlo, multivariate methods, or other methods). In addition, because a large percentage of the population lives along the coasts of the continental United States, offshore wind could be a renewable resource located close to population centers. Several states are focusing on developing offshore wind resources in areas where onshore wind resources are already well developed. However, some offshore projects, such as the proposed wind farm off Cape Cod, Massachusetts, have been plagued with controversy.

Europe has begun to develop offshore resources, and many large and small projects are already installed, under construction, or in the planning stages. The EU-27 countries have 1.5 GW offshore capacity from a total wind installed capacity of 64.9 GW (IEA, 2008).

WIND POWER IN CHINA

Wind Resource Assessments

With its vast area and long coastline, China has abundant wind resources and great potential for wind-generated electric power. From 2006 to 2009, the Center for Wind and Solar Energy Resources Assessment (CWERA) developed a wind resource map for China (Figure 2-4). This map includes land-based and offshore resources, at a resolution of 5 km × 5 km, and at several different heights. The

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-4 Distribution of wind power density in China at 50 m above ground. Source: China Meteorological Administration.

FIGURE 2-4 Distribution of wind power density in China at 50 m above ground. Source: China Meteorological Administration.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

information was generated through numerical simulations based on historical observations from the period 1971 to 2000 (CAE, 2008; Zhu et al., 2009). Technical potential was analyzed using geographic information systems (GIS) to combine geospatial data (terrain, land use) and exclude certain areas not suitable for development (CWERA/CMA, 2010). Table 2-2 summarizes the parameters and results of this modeling. Basic farmland was also excluded because of China’s strict policy of controlling and protecting farmland. Lands with slopes greater than 4 percent were not considered available for wind power development, and lands with slopes of less than 4 percent have an estimated potential installed capacity of 0–5 megawatts (MW)/km2.

Table 2-2 illustrates that China’s total wind resources for Class 3 and higher are comparable to that of the United States. However, due to exclusions, primarily for altitude, China’s available resources and thus technical potential is much smaller, approximately half the total of the United States’. A large proportion of China’s wind resources are located in Tibet and Qinghai provinces, which are excluded from calculations because of their high (> 3,500 m) altitude.

In 2008, grid-connected installed capacity for wind turbines totaled 9.4 GW, and grid-connected generation was 14,800 GWh/yr, which corresponds to a mean of 1,580 utilization hours per turbine (Li and Ma, 2009). The average capacity factor of ~18 percent for wind power projects in China was lower than expected (Li and Ma, 2009).

Based on the onshore technical capacity potential of 2,380 GW (Table 2-2) and a capacity factor of 25 percent, the estimated technical potential generation is 5.2 million GWh/yr, more than 1.5 times China’s total electrical generation (3.2 million GWh) for 2007. Thus, the extractable potential (20 percent of the technical potential) is 1.04 million GWh/yr, or 30 percent of China’s electricity production in 2007. Indeed, this is probably a low estimate, because the data spatial resolution was low and turbine hub height was only 50 m. At a height of 80 m, the extractable potential could increase by about 30 percent (Table 2-1). If the resolution were also increased, which would reveal areas previously unrecognized as having high wind potential, the overall estimate would increase again.

In 2009, CWERA/CMA assessed offshore wind resources once again based on numerical simulations. Based on the guidance “Marine function zoning and planning of China” issued in 2002, offshore regions for port and maritime activities, fisheries, tourism, and engineering are divided according to their potential use, and 60 offshore regions were established for ocean energy as well (such as wave, tide, etc.), leaving only 20 percent of offshore regions open for the development of wind power. The end result (see Table 2-3 and Figure 2-5) shows about 200 GW of offshore wind energy technical potential, for winds of Class 3 or higher, at a height of 50 m above sea level, at depths of 5 m to 25 m (CWERA/CMA, 2010).

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-2 Windy Land Characterization and Wind Energy Technical Potential in Mainland of China for Wind Classes ≥ 3 and Gross Capacity Factors ≥ 30 Percent (without losses)

Wind Land Characterization

 

Key Variables

 

Wind Energy Technical Potential

 

Total Million km2

Excluded Million km2

Available Million km2

Hub Height (m)

Spatial Resolution (km)

Installed Capacity at 5 MW/km2GW

Annual Generation Million GWh

EJ

1.46

0.69

0.77

50

5×5

2380

5.2

19

3.60

2.81

0.79

70

5×5

2850

6.3

23

4.19

3.14

1.05

110

5×5

3800

8.4

30

Source: CWERA/CMA, 2010.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-3 Offshore Wind Power Potential of China (unit: GW)

Grade of Wind Resource Zoning

Wind Resource > Class 4

Wind Power Density ≥ 400 W/m2

Wind Resource > Class 3

Wind Power Density ≥ 300 W/m2

Offshore coverage within 50 km

234

376

Offshore coverage within 20 km

68

140

Offshore coverage between 5 and 25 m isobaths

92

188

Source: CWERA/CMA, 2010.

Development of Wind Resources

The most important factors that influence wind resources and their development are: weather, climate, terrain, and interaction between land and sea. Because wind resources have regional boundaries and temporal inconsistencies, it is important to identify the richest resources for wind power development (Table 2-4). The richest wind resources in China are mainly in the north and along the southeastern coast (CMA, 2006). The poorest wind resource areas are around the Sichuan Basin; in mountainous areas, such as southern Shanxi, western Hunan, western Hubei; mountain areas in Qinling and southern Yunnan; the Yalutsangpo River Valley in Tibet; and the Tarim Basin in Xinjiang (Figure 2-5).

Areas of the northern resource base were selected for development based on five criteria: (1) stable prevailing winds, northerly in winter and southerly in summer; (2) rapid increases in wind speed with height above ground level; (3) not much wind with destructive force; (4) flat terrain, convenient transportation, and good geological conditions for engineering; (5) mainly desert, grassland, and degraded grassland where no crops are grown.

Coastal regions in China offer stable prevailing winds, moderate temperatures, and short distances to load centers. Unfortunately, these areas also have serious disadvantages. First, the coastal area available for wind power development is very small because the regions with the richest wind resources are subject to a 3 km shoreline exclusion. In addition, coastal regions in southeast China have complicated terrain, are subject to turbulent winds and typhoons, and have complicated engineering-geological conditions. Finally, wind power development in these regions would have serious ecological and environmental implications.

The northern Tibetan plateau has more favorable conditions—sparse population, richer wind resources, and thinner air. As an electricity grid and transmission capabilities are created in that region, the wind resources there could be developed.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-5 2006–2009 wind resource data at 50 m hub height and 5 km × 5 km spatial resolution using numerical simulation models. Correspondence of wind power density (wind class) is > 600 W/m2 (> Class 6); 500–600 W/m2 (Class 5); 400–500 W/m2 (Class 4); 300–400 W/m2 (Class 3); 200–300 W/m2 (Class 2); < 200 W/m2 (Classes 1 and 0). Source: China Meteorological Administration.

FIGURE 2-5 2006–2009 wind resource data at 50 m hub height and 5 km × 5 km spatial resolution using numerical simulation models. Correspondence of wind power density (wind class) is > 600 W/m2 (> Class 6); 500–600 W/m2 (Class 5); 400–500 W/m2 (Class 4); 300–400 W/m2 (Class 3); 200–300 W/m2 (Class 2); < 200 W/m2 (Classes 1 and 0). Source: China Meteorological Administration.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-4 Standard of Wind Resource Zoning (unit: W/m2)

 

Richest

Richer

Moderate

Poor

Annual mean wind power density at height of 50 m above ground level

> 150

150–100

100–50

< 50

Source: CWERA/CMA, 2010.

FIGURE 2-6 Offshore wind power potential by numerical methods at 50 m hub height excluding areas subjected to strong and super typhoons in the past 45 years. Correspondence of wind power density (wind class) is > 600 W/m2 (> Class 6); 500–600 W/m2 (Class 5); 400–500 W/m2 (Class 4); 300–400 W/m2 (Class 3); 200–300 W/m2 (Class 2); < 200 W/m2 (Classes 1 and 0). Source: China Meteorological Administration

FIGURE 2-6 Offshore wind power potential by numerical methods at 50 m hub height excluding areas subjected to strong and super typhoons in the past 45 years. Correspondence of wind power density (wind class) is > 600 W/m2 (> Class 6); 500–600 W/m2 (Class 5); 400–500 W/m2 (Class 4); 300–400 W/m2 (Class 3); 200–300 W/m2 (Class 2); < 200 W/m2 (Classes 1 and 0). Source: China Meteorological Administration

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

Summary

China has rich wind resources suitable for development, especially in Inner Mongolia, Jiuquan in Gansu, Hami and Tulufan in Xinjiang, Zhangbei and Chengde in Hebei, Jilin province, western Liaoning province, and along the coast. In total, the wind power potential on the mainland is richer than it is offshore. Regions with good prospects for development of the electric grid, increased transmission capability, and wind power include Yili in Xinjiang, the area around Qinghai Lake, central Gansu, Tongliao and Chifeng in Inner Mongolia, Shaanxi, and Shanxi. Regions with good prospects for developing small-scale, off-grid wind power include Gansu, Ningxia, Shanxi, Henan, Yunnan and Guizhou, and Heilongjiang, southeast Liaoning, and the central mountain area in Shandong.

China also has rich offshore wind resources, all of which have Class 3 or higher winds and are suitable for the development of grid-connected wind farms (Figure 2-6). The offshore regions with the richest wind resources are located in Fujian, southern Zhejiang, and eastern Guangdong. The richest offshore wind resources are in western Guangdong, Hainan, Beibu Gulf in Guangxi, northern Zhejiang, and Bohai Bay. Regions with water less than 25 m deep that are suitable for development are located in Jiangsu, Bohai Bay, and Beibu Gulf. Offshore regions more vulnerable to damage from typhoons are Quanzhou in Fujian, Maoming in Guangdong, the western side of Leizhou Peninsula, and Hainan, Taiwan.

Wind power potential on the mainland for Class 4 winds and higher is 1,130 GW and from Class 3 and higher 2,380 GW. Offshore wind power potential from Class 4 and higher is 92 GW and from Class 3 and higher 188 GW. Overall, the wind power potential is 1,222 GW from Class 4 and higher, 2,568 GW from Class 3 and higher, and 3,940 GW from Class 2 and higher (CWERA/CMA, 2010).

SOLAR POWER IN THE UNITED STATES

The United States has an abundance of solar energy resources. If we use 230 W/m2 as a representative mid-latitude, day/night average value for solar insolation,4 and 8 × 1012 m2 as the area of the continental United States, the yearly averaged, area-averaged, power generation potential is 1.84 million GW (Pernick and Wilder, 2008). Thus, annually, solar power could provide the equivalent of about 16 billion GWh of electricity. Of course, realistic deployment of the technologies to harness this potential is constrained by a variety of factors, including the quality of insolation where facilities are sited, the ability of the grid to accommodate for solar’s variable output, and the presence of other power generation sources in a given area.

4

Solar insolation is the amount of solar energy that strikes a flat surface per unit area per unit of time.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

Solar Photovoltaic Power

Resource Potential

Flat-plate photovoltaic (PV) arrays effectively use both direct and diffuse sunlight, thus enabling deployment over a larger geographic area than is possible with concentrating solar power (CSP) systems. Although the yearly average total insolation varies significantly across the continental United States, the regional variation is approximately a factor of two (see NAS/NAE/NRC, 2010a, Figure 2-2).

Estimates of the rooftop area suitable for the installation of photovoltaic systems have been made for each state. The Energy Foundation and Navigant Consulting (Chaudhari et al., 2004) analyzed rooftop area suitable for PV. This analysis provided estimates for each state, and included flat roofs on commercial buildings, but not steep residential roofs (or roofs not generally facing south). The analysis concluded that 22 percent of available residential rooftop space and 65 percent of commercial building rooftop space was technically suitable for the installation of PV systems.

Combining this estimate of available rooftop area with state-by-state values for average insolation yields a technical solar PV-based peak capacity of 1,500 to 2,000 GW (if conversion efficiencies ranged from 10-15 percent). Assuming a 20 percent capacity factor (slightly more than 5 hours of sunlight per day averaged over the year), this could provide 13 million to 17.5 million GWh/yr of electricity (NAS/NAE/NRC, 2010a). More conservative estimates indicate that existing suitable rooftop space could provide 0.9 million to 1.5 million GWh/yr of PV-generated electricity (ASES, 2007), suggesting that a substantial portion of U.S. electrical demand could be met by solar PV without having to set aside new land for PV development.

Concentrating Solar Power

CSP systems use only the focusable, direct-beam portion of incident sunlight and are thus limited to sites that have abundant, direct normal solar radiation, such as the southwestern United States. Figure 2-7a shows that, despite variations in radiation intensity, all six states there have high levels of insolation. A 2006 analysis by the Western Governors’ Association (WGA) and subsequent refinements by NREL narrowed down suitable land to areas with average insolation of more than 6 kWhm−2day−1; land areas with a slope greater than 1 percent or less than 1 km2, national parks, nature reserves, and urban areas were all excluded (Figure 2-7b) (WGA, 2006a).

This analysis concluded that the southwestern United States has a CSP electricity peak-generation capacity potential of 7,000 to 11,000 GW in the 225,000 km2 of land that has no primary use (Figure 2-7b). With an average annual capacity factor of 25 to 50 percent for CSP (toward the higher end if thermal storage

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

is used), the technical potential of this land area is between 15 million and 40 million GWh of electrical energy per year.

Assuming that 20 percent of the technical potential could become economically feasible, 3 to 8 million GWh could be produced. The current installed CSP capacity in the United States is 0.43 GW. As of March 2010, a total of 8 GW of new capacity was in various stages of development in the United States, with completion expected in 2010 to 2014. These and other international projects are described in the international database SolarPaces, a collaboration among the 16 member countries of the International Energy Agency (IEA) Implementing Agreement on Solar Power and Chemical Energy Systems (IEA, 2010d). Data is available on operational plants and plants under construction or under development.

SOLAR POWER IN CHINA

Resource Assessment

According to the Solar Energy Resource Assessment (CMA, 2008), which is based on radiation data for 1978 to 2007 for more than 700 surface stations, China has ample solar energy resources (see also CAE, 2008). The annual direct and diffuse (collectively referred to as “global”) solar radiation is 14 billion GWh, which is equivalent to 1.7 trillion tons of coal equivalent (tce); the annual direct radiation is 7.8 billion GWh (or 1.0 trillion tce) (CAE, 2008). The distribution of direct radiation is shown in Figure 2-8.

At a modest 10 percent average conversion efficiency, annual global solar radiation would provide 1.4 billion GWh/yr of electricity. Also at a 10 percent conversion efficiency, only 0.23 percent of the land area of China would be required to generate the 3.2 million GWh of electricity generated domestically in 2007. To facilitate the development of solar energy resources, according to the spatial distribution of the annual global solar radiation, China has established four zones based on strength of the resource (Figure 2-9 and Table 2-5).

At present, total rooftop area in China is almost 10 billion m2. About 2 billion m2, 20 percent of that, could accommodate solar PV systems. In addition, solar PV power generation systems could be installed on just 2 percent of the Gobi and other desert land (i.e., 20,000 km2), with a capacity of about 2,200 GW, assuming the same modest 10 percent conversion efficiency for modules. Thus annual solar power generation could total 2.9 trillion kWh, assuming 3.6 hours per day of sun averaged out over a year.

Economic Assessment

The cost of developing and using solar energy resources is directly related to the technology used. At present, China has commercial solar energy utilization

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-7 (a) Total direct normal solar radiation in the Southwest, the most suitable region for concentrated solar power, is shown on the left. Source: National Renewable Energy Laboratory resource analysis upgraded from WGA, 2006a.

FIGURE 2-7 (a) Total direct normal solar radiation in the Southwest, the most suitable region for concentrated solar power, is shown on the left. Source: National Renewable Energy Laboratory resource analysis upgraded from WGA, 2006a.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-7 (b) Direct normal solar radiation, excluding areas with less than 6 kWh/m2/day. Land and slope exclusions are shown on the right, for which the technical concentrated solar power potential of the region is 15 to 40 million GWh (with capacity factors of 25 to 50 percent). Source: National Renewable Energy Laboratory resource analysis upgraded from WGA, 2006a.

FIGURE 2-7 (b) Direct normal solar radiation, excluding areas with less than 6 kWh/m2/day. Land and slope exclusions are shown on the right, for which the technical concentrated solar power potential of the region is 15 to 40 million GWh (with capacity factors of 25 to 50 percent). Source: National Renewable Energy Laboratory resource analysis upgraded from WGA, 2006a.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-8 Annual mean distribution of direct radiation (unit: kWh/m2). Source: China Meteorological Administration.

FIGURE 2-8 Annual mean distribution of direct radiation (unit: kWh/m2). Source: China Meteorological Administration.

technology, such as solar water heaters and crystalline-silicon PV technologies. However, solar thermal power generation technologies are in still in the development and demonstration phases.

According to an assessment of solar water heater cost and practical use, by Beijing Tsinghua Solar Applied Technology Co. Ltd, the expected cost of solar water heaters is between 0.05 and 0.2 Yuan/kWh, depending on the level of internal consumption and export markets, with an average level of about 0.13 Yuan/kWh. Costs for power generation are an order of magnitude greater—presently, the cost of solar PV-generated power ranges from 1.5 to 3.0 Yuan/kWh, depending on solar energy resource zoning (Table 2-6).

BIOMASS FOR BIOPOWER

Biomass is an umbrella term that encompasses a variety of resources, each with its own characteristics (e.g., solid vs. liquid vs. gas; moisture content; energy content; ash content; emissions impact). The types of biomass for energy production fall into three broad categories: (1) wood/plant waste; (2) municipal solid waste and landfill

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-9 Solar energy zones characterized in Table 2-5.

FIGURE 2-9 Solar energy zones characterized in Table 2-5.

TABLE 2-5 Solar Energy Zoning and Distribution

 

Zone

Mean Solar Radiation (kWh/m2·a)

Percent of China’s Territory

Distribution

Richest

I

≥ 1,750

17.4

Most of Tibet, south of Xinjiang, west of Qinghai, Gansu, and Inner Mongolia

Richer

II

1,400~1,750

42.7

North of Xinjiang, northwest of China, east of Inner Mongolia, Huabei, north of Jiangsu, Huangtu Plateau, east of Qinghai and Gansu, west of Sichuan, Hengduan mountain, coastal of Fujian and Guangdong, Hainan

Rich

III

1,050~1,400

36.3

Hilly county in southeast of China, the reaches of Hanshui River, west of Sichuan, Guizhou, and Guangxi

Moderate

IV

≤ 1,050

3.6

Parts of Sichuan and Guizhou

NOTE: Regions with rich solar energy, including richest, richer, and rich zones, account for more than 96 percent of China’s territory.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-6 Estimated Production Costs and Prices of Solar Energy Power Generation and Estimated Potential Capacity of the Chinese Solar Resource

Solar Energy Zoning

I

II

II-III

III

Total solar radiation (kWh/m2·a)

2,250

1,740

1,400

1,160

Annual utilization hours of solar powera

1,700

1,300

1,050

870

Estimated price (Yuan/kWh)

1.5

2.0

2.5

3.5

Estimated production costa (Yuan/kWh)

1.3

1.7

2.1

3.0

Solar power potential (thousand GWh)

700

670

620

210

a After the 1.5 Yuan/kWh subsidy for grid-connected solar power.

gas (LFG); and (3) other biomass products, such as agricultural by-products, biofuels, and selected waste products, such as tires. Crops dedicated to energy production currently represent an insignificant portion of the U.S. and Chinese biomass energy supplies. However, growing interest in using biomass to produce alternative liquid transportation fuels (biofuels) is beginning to change the methodology of documenting biomass usage. A particularly attractive feature of biomass is that, as a chemical energy source, it is available when needed. This feature also makes it attractive for competing applications, such as for the production of transportation fuel.

BIOPOWER IN THE UNITED STATES

Biomass Resources

A U.S. Department of Agriculture (USDA) and Department of Energy (DOE) study (2005) identifies the potential for using 1.3 billion dry tons (1 dry ton = 1,000 kg) per year of biomass for energy without adversely affecting food production. This estimate involved 448 million acres (1.8 × 1,012 m2) of agricultural land, both croplands and pastures, and 672 million acres of forestland (2.7 × 1,012 m2) (USDA/DOE, 2005). Collectively, the total area assumed to be available for biomass is slightly more than 57 percent of the total land area of the lower 48 states (NAS/NAE/NRC, 2010a).

However, the amount of land actually used for biomass production will be substantially less than the total available. For example, at 2.5 tons/acre/year and at 5/tons/acre/year, the land area required for 1.3 billion tons/year would be 423 million acres and 260 million acres, respectively. As discussed below, when supply projections based on the cost are used, the estimates are significantly less than the theoretical potential. Economic supply potential in 2025 ranges from 500 to 700 million tons/year, which would require 100 million acres (500 million tons at 5 tons/acre/year) to 280 million acres (700 million tons at 2.5 tons/acre/year).

The amount of biomass that can sustainably be removed from domestic agricultural lands and forestlands is 190 million dry tons annually, with about

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

142 million dry tons coming from forestland and the remainder coming from cropland. Only about 20 percent of this is now being used for biomass production. The USDA/DOE report projected that approximately 370 million tons (twice the present biomass production) could be made available sustainably from 672 million acres of forestland. However, this would require (1) using wood instead of burning it for forest management, (2) using pulp residues, and (3) using logging residues for power generation.

The USDA/DOE report also projected that in 35 to 40 years agricultural lands (cropland, idle cropland, and cropland pasture), which produce approximately 50 million tons of biomass per year, have the potential to yield nearly 1 billion dry tons of biomass. This would be a 20-fold increase in the yield of sustainable biomass. Of the projected 1 billion dry tons, 300 to 400 million tons would come from crop residues, and 350 million tons would result from replacing other land uses on some 40 million acres with high-yield perennial biomass crops.

The estimate in the billion-ton study by USDA/DOE was for future potential biomass resources. Another study by NREL (Milbrandt, 2005) shows a different geographical distribution of the biomass resource base (Figure 2-10). The NREL study, based on currently available biomass resources, includes county-level assessments of (1) agricultural and forest residues, (2) urban wood (secondary mill residues, municipal solid waste [MSW] wood, tree trimmings, and construction/demolition wood), and (3) methane emissions from manure management, landfills, and domestic wastewater treatment facilities.

According to the USDA/DOE study, a yield of 1.3 billion dry tons per year of biomass would require increasing the yields of corn, wheat, and other small grains by 50 percent; doubling residue-to-grain ratios for soybeans; developing more efficient residue harvesting equipment; managing croplands with no-till cultivation; growing perennial crops primarily dedicated to energy purposes on 55 million acres of cropland, idle cropland, and cropland pasture; using animal manure not necessary for on-farm soil improvement; and using a larger fraction of other secondary and tertiary residues for biomass production. Attaining these increased crop yields and collecting these materials would require new technologies, such as genetic engineering.

The billion-ton estimate was based on the assumption that agricultural lands in the United States could potentially provide more than 1 billion dry tons of sustainably collectable biomass, while continuing to meet food, feed, and export demands (NAS/NAE/NRC, 2010a). This included 446 million dry tons of crop residues, 377 million dry tons of perennial crops,5 87 million dry tons of grains used for biofuels, and 87 million dry tons of animal manure, process residues, and other residues.

Another estimate was provided by the Panel on Alternative Liquid Transportation Fuels, part of the America’s Energy Future project of the National

5

The perennial crops are crops dedicated primarily to energy and other products and will likely include a combination of grasses and woody crops.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-10 Total biomass available in the United States by county. Source: Milbrandt, 2005.

FIGURE 2-10 Total biomass available in the United States by county. Source: Milbrandt, 2005.

Academies (NAS/NAE/NRC, 2009b). Similar to NREL projections, this estimate projects an annual supply of 400 million dry tons of lignocellulosic biomass sustainably produced using technologies and management practices available in 2008. The panel projects that the supply could be increased to about 550 million dry tons by 2020 from dedicated energy crops, agricultural and forestry residues, and municipal solid waste with minimal impacts on U.S. food, feed, and fiber production and with minimal adverse environmental impacts. The panel also considered sustainability factors, such as maintaining soil carbon levels and crop productivity in subsequent years.

Economic Assessment

As discussed above, a number of studies have provided estimates of biomass availability and costs. In a review of these studies by Gronowska et al. (2009), the authors differentiated between inventory studies of existing and potential biomass resources and economic studies that take into account the cost of supply, generally referred to as biomass supply curves. Inventory studies provide estimates ranging

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

from 190 to 3,850 million dry tons annual biomass yield. Supply curve estimates range from 6 to 577 million dry tons annually, depending on feed category and price. Gronowska et al. noted that in most studies, future biomass supplies are projected to be a mix of agricultural residues and dedicated crops, with smaller amounts of residual woody materials. Estimates by Oak Ridge National Laboratory (ORNL) (Perlack et al., 2005; Walsh et al., 2000), NREL (Milbrandt, 2005), the National Academies (NAS/NAE/NRC, 2009b), EIA (Haq and Easterly, 2006), and M&E Biomass (Walsh, 2008) are compared in Figure 2-11. It is unclear whether agricultural practices using bioengineered plants will be sustainable, even if photosynthesis can be enhanced through genetic modification. Even with today’s candidate energy crops (e.g., willow, miscanthus, poplar, switchgrass) it is not clear what fraction of biomass must be left in the fields to ensure soil health, although a trend toward conservation tillage, that is, leaving at least 30 percent of the soil covered with residue, would reduce the amount of biomass available for other uses (NRC, 2010b).

Supply curves to estimate electricity from biomass ($/kWh versus kWh/yr) have yet to be developed. A sample supply curve from the M&E Biomass study (Walsh, 2008) is shown in Figure 2-12. Walsh (2008) relied on default biomass supply costs from the NREL (Milbrandt, 2005) study.

NREL has also developed a Bio-power Tool,6 an interactive geospatial application that enables users to view biomass resources, infrastructure, and other relevant information and to query the data and conduct initial screening analyses. Users can select a location on the map, quantify the biomass resources available in a defined radius, and estimate the total thermal energy or power that could be generated by recovering a portion of that biomass. This tool is useful for refining the site-identification process but does not eliminate the need for on-site resource evaluation.

Electricity Generation from Biomass

Based on 2005 biomass production levels, full use of the 190 million dry tons of sustainable biomass produced in the United States, at 17 GJ (1 GJ = 1 × 109 J)/dry ton, and at 35 percent efficiency for the conversion of heat from biomass combustion into electrical energy, would provide 1.1 EJ of energy.7 In other words, 100 percent of the sustainable biomass produced domestically in 2005, if used entirely for electricity generation, would produce 0.306 million GWh/yr of electricity, or 7.3 percent of the 2007 U.S. domestic electricity generation. Using a resource average value of ~500 million tons of biomass (NAS/NAE/NRC, 2010b), a total of 0.8 million GWh/yr of electricity could be produced, or 19 percent of 2007 U.S. electricity generation. Increasing available biomass to 1 billion tons and using it solely for electricity generation would produce 6 EJ, which is equal

6

Available online at http://rpm.nrel.gov/biopower/biopower/launch.

7

1.9 × 108 tons × (1.7 × 1010 J/ton) at 35 percent electric generation efficiency.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-11 Past and current inventories and potential supplies at specific prices for various types of biomass in the United States. CRP = Conservation Reserve Program. Source: Walsh, 2008.

FIGURE 2-11 Past and current inventories and potential supplies at specific prices for various types of biomass in the United States. CRP = Conservation Reserve Program. Source: Walsh, 2008.

to 1.6 million GWh/yr of electricity, representing approximately 40 percent of domestic electricity generation for 2007.

However, a plausible scenario might be that 75 percent of this biomass would be used to produce cellulosic ethanol or other biofuels, and only 25 percent would be available for electricity generation. In that case, 250 million tons of biomass, which is projected to be potentially available in 35 to 40 years if more than 60 percent of the land area of the continental United States were dedicated to producing biomass, would produce 0.416 million GWh of electricity, 10 percent of the 2007 U.S. electricity generation. This represents more than 7 times the actual electricity generation from biomass in 2005 (0.054 million GWh, which accounted for slightly more than 1 percent).

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-12 Biomass supply curves indicating how much feedstock can be delivered to a conversion facility at a certain price for various scenarios from today to 2025. Source: Walsh, 2008 (plus $15/ton transportation and handling costs).

FIGURE 2-12 Biomass supply curves indicating how much feedstock can be delivered to a conversion facility at a certain price for various scenarios from today to 2025. Source: Walsh, 2008 (plus $15/ton transportation and handling costs).

BIOPOWER IN CHINA

China’s biomass energy resources include straw and other agricultural wastes, forestry and forest product processing waste, animal manure, dedicated energy crops, organic effluents from industry, municipal wastewater, and municipal solid waste (MSW). Of about 600 million tons of crop straw produced every year, nearly 300 million tons (or around 150 million tons of coal equivalent (tce)), could be used as fuel (NDRC, 2007). Of about 900 million dry tons of waste from forestry and forest product processing available every year, nearly 300 million tons (or about 200 million tce) can be used for energy production. In addition, there are large areas of marginal lands in China that could be used to cultivate energy crops and plantations. Biogas and MSW are also biomass resources with good potential for development. At present, China’s total annual biomass resource suitable for energy conversion is roughly equivalent to 1,300 TWh, or approximately one-third of China’s total electricity consumption in 2009. When accounting for further development (improved collection methods for agricultural waste, increases in industrial and municipal effluents), this resource base could eventually double.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

TABLE 2-7 Differences in Geothermal Electric Power Production Assessments Conducted by the U.S. Geological Survey

 

1979

2008

Temperature and depth

> 150ºC and <3 km

> 90ºC and up to 6 km (Alaska 75ºC)

Number of identified systems

52 high temperature

241 high and moderate temperature

Characterization of identified systems

Poor

Abundant exploration and production data

Treatment of reservoir performance

Idealized

Improved models with Monte Carlo analysis for uncertainties

Undiscovered resources

Rough estimates

Better quantitative estimates

Enhanced geothermal systems

Mentioned but not estimated

Included; analysis and methodological development continues

Source: Williams and Pierce, 2008.

GEOTHERMAL POWER IN THE UNITED STATES

Hydrothermal Energy

Geothermal energy exists as underground reservoirs of steam, hot water, and hot dry rocks in Earth’s crust (NAS/NAE/NRC, 2010a). In its first national assessment of geothermal energy, the U.S. Geological Survey (USGS, 1979) focused on two categories of hydrothermal resources: (1) identified systems with the electricity generation potential of 0.18 million GWh (23 GW), which were geologically assured and economical (called reserves) or could become economical in time; (2) undiscovered resources with an electric power potential of 0.8 million GWh (~100 GW); these resources were technically recoverable and could become reserves over time. Taken together the resources in these two categories represent one-quarter of the electric power generated in the United States in 2007.8

Some 30 years later, in a new assessment using improved science and technology, USGS found an even greater potential (Williams et al., 2008). Results of the 2008 assessment (Table 2-7) indicate a mean electric power capacity potential of 9 GW from identified geothermal hydrothermal systems in 13 states. The estimate ranges from 3.7 GW with 95 percent probability to 16.5 GW with 5 percent probability. Twenty percent of the systems with reservoir temperatures of more than 150ºC account for 80 percent of the power potential; most systems have less than 5km3 of reservoir volume (Figure 2-13).

The full development of just the conventional, identified systems would increase geothermal power capacity by approximately 6.5 GW. By comparison, the 2005 installed geothermal capacity of 2.5 GW grew to 3 GW in 2008, adding

8

Geothermal power capacity of 1 MWe generates 7.8 GWh/yr at 90 percent capacity factor.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-13 Map showing the location of identified moderate- and high-temperature geothermal systems in the United States. Each system is represented by a black dot. Source: Williams and Pierce, 2008.

FIGURE 2-13 Map showing the location of identified moderate- and high-temperature geothermal systems in the United States. Each system is represented by a black dot. Source: Williams and Pierce, 2008.

0.11 GW in 2008 alone. The geothermal baseload power generation was 15,000 GWh (Cross and Freeman, 2009).

The 2008 USGS assessment estimated that the mean capacity potential of undiscovered geothermal systems was 30 GW, ranging from 7.9 GW (95 percent probability) to 73 GW (5 percent probability) (Figure 2-14).

Prior assessments for the western states identified 13 GW of potential electric power capacity from 140 sites (WGA, 2006b). With advances in geothermal technology, development, and power-generating operations, 5.6 GW of this potential was considered viable for commercial development by 2015. A nationwide panel of experts estimated that the shallow hydrothermal resource base had an availability of 30 GW, with an additional potential of 120 GW from unidentified hydrothermal resources that have no surface manifestations (Green and Nix, 2006). The panel of experts estimated that 10 GW could be developed by 2015.

These estimates were characterized as having significant uncertainties and did not constitute a resource assessment. Nevertheless, they clearly indicate that geothermal resources can be a significant domestic source of energy in the United States. The geothermal power capacity potential for identified resources from the WGA study is well within the range of the 2008 USGS assessment.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-14 Sample map (from a series of 28 spatial models) showing the relative favorability of occurrence for geothermal resources in the western contiguous United States. The other models differ in details but show generally similar favorability patterns. Warmer colors equate with higher favorability. Identified geothermal systems are represented by black dots. Source: Williams and Pierce, 2008.

FIGURE 2-14 Sample map (from a series of 28 spatial models) showing the relative favorability of occurrence for geothermal resources in the western contiguous United States. The other models differ in details but show generally similar favorability patterns. Warmer colors equate with higher favorability. Identified geothermal systems are represented by black dots. Source: Williams and Pierce, 2008.

Enhanced Geothermal Systems

Enhanced geothermal systems (EGSs) are engineered reservoirs created to extract heat from low-permeability and low-porosity rock formations. Permeability is enhanced by causing existing fractures to slip and propagate or by increasing fluid pressure to create new cracks. EGSs tap the vast heat resources available from temperature gradients between the surface and depths of up to 10 km.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

The 2008 USGS resource estimate for unconventional EGSs is more than an order of magnitude larger than the combined estimates for both identified and undiscovered conventional geothermal resources (Figure 2-14). If successfully developed, EGSs could provide an installed geothermal electric power generation capacity equivalent to about one-half of the currently installed electric power generating capacity in the United States. The mean electric power capacity potential from unconventional geothermal resources (high temperature, low permeability) EGSs is 518 GW, with a range of 345 GW (95 percent probability) to 728 GW (5 percent probability). The mean electric power generation potential corresponds to 4 million GWh/yr, as much power as was generated in the United States in 2007.

When USGS used a different methodology to test its results, the studies confirmed the large potential of EGS in the United States. The geothermal energy resource base located beneath the continental United States (total amount of heat at a depth of 10 km) is estimated to be in excess of 13 million EJ (3.6 trillion GWh), with an extractable portion of 200,000 EJ (MIT, 2006). At a conversion efficiency rate of 15 percent, the extractable geothermal resource could then, in principle, provide 30,000 EJ of electric energy (NAS/NAE/NRC, 2010a). Significant research and development will be necessary to develop the technology to take advantage of this energy source and to improve measurements of its potential.

The rate of extraction will be an important factor in how well we use this resource. The mean geothermal heat flux over land at Earth’s surface is approximately 100 mW/m2 and in many areas is significantly less. The NAS/NAE/NRC (2010a) study estimated the extractable electric power density from the geothermal resource on a renewable basis (i.e., heat being drawn down is restored by the natural geothermal flux) to be about 10 mW/m2, and so producing even 100 GW would require land area in excess of the entire continental United States.

In practice, the in-place geothermal heat would have to be extracted at rates in excess of the natural geothermal heat flux (NAS/NAE/NRC, 2010a). In the MIT (2006) analysis of resource potential, heat mining was limited by assuming that geothermal reservoirs would be abandoned when the temperature of the rocks fell by 10 to 15ºC, reservoirs were assumed to have a lifetime of 30 years, with periodic re-drilling, fracturing, and hydraulic simulation and were estimated to be able to recover to their original temperature conditions within 100 years of abandonment. Thus, if 10 percent or less of the stored heat is mined at any one time, EGS could be considered a renewable resource (NAS/NAE/NRC, 2010a).

GEOTHERMAL POWER IN CHINA

A preliminary estimate of the capacity of high-temperature geothermal resources in China is 5.8 GW, and the capacity of low-temperature geothermal resources is 14.4 GW. Although China is a leader in direct thermal use of geothermal resources, with 3.7 GWt (a measure of thermal [not electric] power,

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×

equivalent to 12.6 TWh/yr), and has the rock formations for these systems, EGSs have not been assessed (Bertani, 2005).

The most important geothermal plant in operation, with a capacity of 25 MW, is located in Yangbajain, Tibet. Energy is generated from a shallow reservoir (depth 200 m) that covers about 4 km2; the temperature is 140 to 160ºC. The annual energy production of this plant is approximately 100 GWh, about 30 percent of the needs of the Tibetan capital, Lhasa. This field also has the potential of producing 50 to 90 MW from deep reservoirs (250 to 330ºC at a depth of 1,500 to 1,800 m) beneath the shallow Yangbajian field (Bertani, 2005). Another plant with a capacity of 49 GW is under construction in the Tengchong area, Yunnan province.

HYDROKINETIC POWER IN THE UNITED STATES

Wave, Tide, and River Energy

Hydrokinetic energy is energy associated with the flow of water, such as waves and water currents, including tides, rivers, and oceans. In general, these resources would only be sufficient to meet a small percentage of overall U.S. demand. The Electric Power Research Institute (EPRI) assessed total U.S. wave energy potential (EPRI, 2005) and found that all the wave energy off the Pacific coast could produce 0.44 million GWh/yr, and the wave energy from the Northeast and Mid-Atlantic coast could produce 0.12 million GWh/yr (Figure 2-15). When factoring in generation losses (10 to 15 percent), the total electric generation potential is about 0.07 million GWh for the entire continental U.S. wave energy resource (NAS/NAE/NRC, 2010a). The largest U.S. wave resource is off southern Alaska, which has an estimated resource base of 1.25 million GWh/yr (EPRI, 2005), but collecting and transmitting this as electrical energy to consumers in the lower 48 states represents a significant challenge.

The EPRI study also examined tidal energy potential from sites in Alaska, Washington, California, Massachusetts, Maine, and New Brunswick and Nova Scotia (Canada). The total combined resource was estimated to have an annual average electricity generation potential of 152 MW, which corresponds to an annualized electricity production of 1,300 GWh/year (EPRI, 2005). Another EPRI study (EPRI, 2007) focused on the electric energy potential of river currents and estimated a value of 0.11 million GWh/year.

The resource potential for theoretical, technical, and practical energy extraction from all of these sources will have to be characterized more comprehensively. Like wind energy and technology, the interplay between these resources and new technologies might lead to the identification of more resources.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
×
FIGURE 2-15 U.S. wave-energy resources. Source: EPRI, 2005.

FIGURE 2-15 U.S. wave-energy resources. Source: EPRI, 2005.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
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HYDROKINETIC POWER IN CHINA

Up to now, China has only developed eight small-scale, tidal-energy stations with total installed power of 6 MW. The largest, Jiangxia tidal station in Zhejiang Province, constructed in 1974, is also the largest one in Asia and the third largest in the world. With six machines, this station has a total of 3.9 MW installed power. Additional tidal barrage plants in Baishakou and Haishan provide up to 640 kW and 150 kW, respectively. Many demonstration-stage wave-power stations of several tens to hundreds of kW are used for light navigation in coastal areas. In the near future, ocean power research and development will be increased and practical applications could be expanded, but still for small-scale power supply.

INTEGRATED RESOURCE PLANNING

Clean and Diversified Energy for the West, a project of the U.S. WGA is identifying ways to increase renewable energy, energy efficiency, and clean energy technologies in the mix for meeting the overall energy needs of the western United States.9 Since 2006, WGA has used multiple resource assessments to inform its decisions about the development of 30 GW of clean energy by 2015.

In the first phase of the project, Western Renewable Energy Zones (WREZ), “hubs” that have the potential to contribute to a Western Interconnection, were identified for the purpose of evaluating interstate transmission lines for future phases of the initiative. Figure 2-16 shows the WREZ Initiative Hub Map with graphical representations of regional renewable resource potentials sized in proportion to the total amount of electricity (in TWh) that could be produced over the course of a year from resources in the Qualified Resource Areas (QRAs) (Pletka and Finn, 2009). Resource estimates do not include environmentally and technically sensitive areas, and they discount the remaining resource potential to account for unforeseen development constraints.

In some cases, the energy generating potential of a QRA is reduced to account for certain environmental sensitivities identified by state wildlife agencies, but little consideration is given to construction logistics or costs, permitting, or cultural and other land-use concerns related to specific sites. These factors are considered in other phases of the project, which includes a public consultation process (WGA, 2009). All resources that meet the minimum quality thresholds defined by the Zone Identification and Technical Analysis Working Group are shown on the map.

According to the WGA (2009, p.1) report:

The resources quantified in each hub include only the highest quality wind and solar resources as well as geothermal sites, biomass, and hydropower with known commercial potential. Because the quality criteria for minimum wind and solar resource quality vary

9

See WGA Policy Resolution 06-10 available online at http://www.rnp.org/news/PR_PDF_files/WGA/clean-energy.pdf.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
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FIGURE 2-16 QRAs showing potential for electricity generation from a variety of renewable sources (biomass is not shown; only some part of the Canadian QRAs shown). Maps like this one were the first step in planning for renewable electricity and new transmission and distribution on a regional basis with input from the public. Source: WGA, 2009.

FIGURE 2-16 QRAs showing potential for electricity generation from a variety of renewable sources (biomass is not shown; only some part of the Canadian QRAs shown). Maps like this one were the first step in planning for renewable electricity and new transmission and distribution on a regional basis with input from the public. Source: WGA, 2009.

from state to state, resources that did not meet the state’s general quality thresholds were labeled “non-WREZ” resources. These include low-quality wind, solar thermal, solar PV, undiscovered conventional geothermal potential, enhanced geothermal systems, and other viable renewable resources. Thus, the assessment of conventional geothermal resources was limited to British Columbia, California, Idaho, Nevada, Oregon, and Utah which have known high-potential conventional geothermal resources. Biomass resources are also quantified as part of the WREZ supply curve analysis for each QRA, but they are not shown on the map.

WGA has also developed a transmission model and is proceeding to facilitate construction of utility-scale renewable energy plants and transmission systems. In this phase, multi-layer maps are being prepared to visualize technology-specific filters to refine QRAs and capture best sites; map layers show land use and areas excluded for wildlife protection and other environmental and ecological reasons. An interactive tool is under development that will enable planners to take these and other criteria into consideration and identify barriers to development. All

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
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phases of the process, results, and models are available on the WGA web site (WGA, 2009).

FINDINGS

Both the United States and China have significant renewable energy resources that have the potential, in principle, to provide more electric power than the total existing installed peak capacity and more electric energy annually than the total amount of electricity consumed in each country in 2009. This resource base is spread widely across the both countries.

Solar and wind renewable resources have significantly more total energy and power potential than other domestic renewable resources. Although solar intensity varies across both nations, land-based solar resources provide a yearly average of more than 10 million terawatt hours, which exceeds, by several thousand-fold, present annual U.S. or Chinese electrical energy demand. Hence, even with modest conversion efficiency rates, solar energy is capable, in principle, of providing enormous amounts of electricity without stress to the resource base. Land-based wind resources are capable of providing at least 20 percent, and in some regions more, of current electrical energy demand in both countries. Other (non-hydroelectric) renewable resources can also contribute significantly to the electrical energy mix in some regions.

The United States is conducting increasingly comprehensive and higher resolution assessments of the technical potential of its renewable resources. These assessments often include initial estimates of economic potential, combining supply curves with cost of delivered electricity for a certain amount of resource. Some Chinese resources have only been assessed at the inventory level, mostly at low resolution. Assessments that link high-resolution knowledge of a resource base and technological progress for wind power and other renewables would be helpful to China. A reassessment of China’s wind resources using higher resolution wind resource data and higher turbine hub heights could help to identify new wind development sites. A similar assessment in the United States led to a reevaluation of wind resource potential in many states. Additional areas where the United States could lend expertise include measurements of direct normal incidence radiation (for CSP potential) and EGS mapping. In both instances, these assessments should include regional water availability, since it is a potential limiting factor in the large-scale deployment of CSP or EGS.

Scenario modeling (combining geographic information systems with estimated economic resource assessments, renewable technology development with time, current and possible evolution of transmission infrastructure, and balancing costs) is becoming increasingly important for planning and rational development of both traditional and renewable energy resources. It requires the use of coupled models that enable exploration of a large number of scenarios and the consequences of their deployment. China and the United States can collaborate in

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
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this area to identify ways to reduce implementation costs through integrated resource planning and scenario modeling efforts.

Biomass resource assessment collaborations among U.S. DOE and the Chinese government, academia, and industry are ongoing for biofuels feedstock supply curve developments, but these conversion technologies are still under development. Some biopower technologies such as co-firing are the most cost effective and could be developed for appropriate regions of the country using residues if an efficient collection infrastructure is established. Mapping multiple layers of resources and infrastructure may facilitate co-development of biopower and biofuels and capitalize on the economic potential of biorefineries.

Modeling of hydrokinetic energy, which is just starting in both countries, has great uncertainties because of weather-related disasters and unpredictability. Offshore resources are also subject to weather changes and disasters. To ensure that resource assessment models include risk assessment for severe weather conditions, the United States and China could collaborate to develop and test best locations and minimize financial risk.

RECOMMENDATIONS

  • China and the United States should collaborate on mapping integrated resource and development options at regional scales. Such multi-resource maps and evaluation can help identify options for distributed generation, potential resource constraints (e.g., water availability for thermoelectric power), and least cost routes for needed transmission.

  • Researchers, modelers, and systems operators from both countries should collaborate on developing the software and computer models to support more integrated supply models.

Suggested Citation:"2 Resource Base." National Academy of Engineering and National Research Council. 2010. The Power of Renewables: Opportunities and Challenges for China and the United States. Washington, DC: The National Academies Press. doi: 10.17226/12987.
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The United States and China are the world's top two energy consumers and, as of 2010, the two largest economies. Consequently, they have a decisive role to play in the world's clean energy future. Both countries are also motivated by related goals, namely diversified energy portfolios, job creation, energy security, and pollution reduction, making renewable energy development an important strategy with wide-ranging implications. Given the size of their energy markets, any substantial progress the two countries make in advancing use of renewable energy will provide global benefits, in terms of enhanced technological understanding, reduced costs through expanded deployment, and reduced greenhouse gas (GHG) emissions relative to conventional generation from fossil fuels.

Within this context, the U.S. National Academies, in collaboration with the Chinese Academy of Sciences (CAS) and Chinese Academy of Engineering (CAE), reviewed renewable energy development and deployment in the two countries, to highlight prospects for collaboration across the research to deployment chain and to suggest strategies which would promote more rapid and economical attainment of renewable energy goals.

Main findings and concerning renewable resource assessments, technology development, environmental impacts, market infrastructure, among others, are presented. Specific recommendations have been limited to those judged to be most likely to accelerate the pace of deployment, increase cost-competitiveness, or shape the future market for renewable energy. The recommendations presented here are also pragmatic and achievable.

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