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.



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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 geother- mal and hydrokinetic energy sources under development in the United States that may have applicability in China. China is at a comparatively early stage of assess - ing 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. 

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4 ThE POWER OF RENEWAbLES restrictions (e.g., terrain, weather, environmental conditions, ecological limita - tions, 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, eco- nomic 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 poten - tial 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 genera - tion (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.

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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 Installed Annual Total Excluded Available Hub height Spatial resolution capacity at 5 generation million km2 million km2 million km2 m km MW/km2 GW 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 x 5 7,000–8,000 15–20 50–60 Elliott et al., 2010 AWS Truewind, LLC 2.57 0.47 2.10 80 0.2 × 0.2 10,500 36.9 135 and NREL, 2010 5

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6 ThE POWER OF RENEWAbLES WIND POWER IN THE UNITED STATES In a seminal work by Elliott et al. (1991), the total estimated electricity tech - nical 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 character- ization and use of windy lands, and increased hub heights, the technical poten - tial 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 extrac - tion could affect the geographic distribution and/or the inter- and intra-annual variability of winds, or might even alter the external conditions for wind devel- opment and climate conditions. Thus, model calculations suggest that, in addi - tion 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.

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Wind speeds at 50m 70m 10 0m 2-1.eps 70 m, and 100 7 FIGURE 2-1 Comparison of the wind energy resource at 50 m,landscape m for the state of Indiana, United States. Source: DOE, 2008c. 5 bitmaps with some vector patchwork

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8 ThE POWER OF RENEWAbLES 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 deploy - ment of renewable electricity products, including manufacture, installation, and operations; required capital investments and economic development in the pres- ence (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.

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 RESOURCE bASE 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 genera- tion (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 opera - tions 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 esti- mated at 907 GW for distances of 5 to 50 nautical miles offshore (Musial and

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160 0 Onshore Offshore 140 Class 7 Class 7 Class 6 Class 6 120 Class 5 Class 5 Class 4 Class 4 Class 3 Class 3 100 80 60 Levelized Cost of Energy 40 (Dollars per Megawatt-hour) 20 0 200 400 600 800 1000 Quantity Available (Gigawatts) 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. R 4.7

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Transmission Lines Voltage (kV) 345-499 500-699 700-799 1000 (DC) 2-3.eps FIGURE 2-3 A concept of transmission with one technically feasible transmission grid of 765 kV overlayed on wind resource data combining landscape low- and high-resolution datasets used to model the 20 percent wind scenario using NREL’s Regional Energy Deployment System (ReEDS)  bitmap

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 ThE POWER OF RENEWAbLES 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, includ - ing 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 uncer- tainty 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 capac- ity 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

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

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5 ThE POWER OF RENEWAbLES TABLE 2-7 Differences in Geothermal Electric Power Production Assessments Conducted by the U.S. Geological Survey 1979 2008 150oC > 90oC and up to 6 km (Alaska 75oC) Temperature and depth > and <3 km Number of identified systems 52 high temperature 241 high and moderate temperature Characterization of identified Poor Abundant exploration and production systems data Treatment of reservoir Idealized Improved models with Monte Carlo performance analysis for uncertainties Undiscovered resources Rough estimates Better quantitative estimates Enhanced geothermal Mentioned but not Included; analysis and methodological systems estimated 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 assess- ment 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 geo - logically 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 technol - ogy, 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 prob - ability. Twenty percent of the systems with reservoir temperatures of more than 150° C account for 80 percent of the power potential; most systems have less than 5 km3 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.

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5 RESOURCE bASE 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. 2-13.eps bitmap w 2 blank masks 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 tech - nology, 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 availabil- ity of 30 GW, with an additional potential of 120 GW from unidentified hydro - thermal 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.

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54 ThE POWER OF RENEWAbLES FIGURE 2-14 Sample map (from a series of 28 spatial models) showing the relative fa- vorability of occurrence for geothermal2-14.eps the western contiguous United States. resources in 2 bitmaps, several blank masks 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.

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55 RESOURCE bASE 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 gen - erating 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). Signifi- cant 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 approxi - mately 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 15°C, 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 geother- mal resources in China is 5.8 GW, and the capacity of low-temperature geo- thermal 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,

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56 ThE POWER OF RENEWAbLES 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 reser- voir (depth 200 m) that covers about 4 km2; the temperature is 140 to 160°C. 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 330°C 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 extrac - tion 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.

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Southern AK ME, NH, MA, RI, NY, NJ 1250 TWh per Year 120 TWh per Year Midway Island Northern HI WA, OR, CA 300 TWh per Year 440 TWh per Year Hawaii Johnson Island FIGURE 2-15 U.S. wave-energy resources. Source: EPRI, 2005. R 2.7 57

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58 ThE POWER OF RENEWAbLES 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 sev - eral 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 pro - portion 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.

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

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60 ThE POWER OF RENEWAbLES 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 nor- mal 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 esti - mated 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 conse - quences of their deployment. China and the United States can collaborate in

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6 RESOURCE bASE 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 con - ditions, 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.

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