Special Report - Contribution to Special Report Renewable Energy Sources (SRREN)

The theoretical potential for wind, as estimated by the global annual flux, has been estimated at 6,000 EJ/yr (Rogner et al., 2000). The global technical potential for wind energy, meanwhile, is not fixed, but is instead related to the status of the technology and assumptions made regarding other constraints to wind farm development.

Nonetheless, a growing number of global wind resource assessments have demonstrated that the world’s technical potential for wind power exceeds current global electricity production, and that ample technical potential exists in most regions of the world to enable significant wind energy deployment relative to current levels. The wind resource is not evenly distributed across the globe, however, and a variety of other regional factors are likely to restrict growth well before any absolute global technical resource limits are encountered.

As a result, wind energy will not contribute equally in meeting the needs of every country. This section summarizes available evidence on the size of the global technical potential of the wind energy resource, the regional distribution of that resource and the possible impacts of climate change on wind energy resources. It focuses on longterm average annual technical potential; for a discussion of interannual, seasonal and diurnal fluctuations and patterns in the wind resource, as well as shorter-term wind power output variability.

Global technical potential:
A number of studies have evaluated the global technical potential for wind energy. In general, two methods can be used: first, available wind speed measurements can be interpolated to construct a surface wind distribution; and second, physics-based numerical weather prediction models can be applied.

Studies of the global wind energy resource have used varying combinations of these two approaches. Additionally, it is important to recognize that estimates of the technical potential for wind energy should not be viewed as fixed—the potential will change as wind energy technology develops (e.g., taller towers provide access to better wind, or foundation innovation allows offshore wind farm plants to be developed in greater water depths) and as more is learned about technical, environmental and social concerns that may influence development (e.g., land competition, distance from resource areas to electricity demand centres, etc.).

Synthesizing the available literature, the IPCC’s Fourth Assessment Report identified 600 EJ/yr of onshore wind energy technical potential (IPCC, 2007). Using the direct equivalent method of deriving primary energy equivalence (where electricity supply, in TWh, is translated directly to primary energy, in EJ; the IPCC (2007) estimate of onshore wind energy technical potential is 180 EJ/yr (50,000 TWh/yr), more than two times greater than gross global electricity production in 2008 (73 EJ, or 20,200 TWh).

Of this 180 EJ/y, only 0.8 EJ (220 TWh, 0.4% of the estimated technical potential) was being used for wind energy supply in 2008 (IEA, 2010a). More generally, a number of analyses have been undertaken to estimate the global technical potential for wind energy.

No standardized approach has been developed to estimate the global technical potential of wind energy: the diversity in data, methods, assumptions and even definitions for technical potential complicate comparisons. Consequently, the studies show a wide range of results. Specifically, estimates of global technical potential range from a low of 70 EJ/yr (19,400 TWh/yr) (onshore only) to a high of 450 EJ/yr (125,000 TWh/yr) (onshore and near-shore) among those studies that consider relatively more development constraints (identified as ‘more constraints’).

This range equals from roughly one to six times global electricity production in 2008. If those studies that apply more limited development constraints are also included, the absolute range of technical potential is greater still, from 70 EJ/yr to 3,050 EJ/yr (19,400 to 840,000 TWh/yr). Results vary based in part on whether offshore wind energy is included (and under what assumptions), the wind speed data that are used, the areas assumed available for wind energy development, the rated output of wind turbines installed per unit of land area, and the assumed performance of wind farm plants. The latter is, in part, related to hub height and wind turbine technology. These factors depend on technical assumptions as well as subjective judgements of development constraints, thus there is no single ‘correct’ estimate of technical potential.

Though research has generally found the technical potential for offshore wind energy to be smaller than for onshore wind energy, the technical potential is nonetheless sizable. Three of the studies exclude the technical potential of offshore wind energy; even those studies that include offshore wind energy often do so only considering the wind energy technology likely to be deployed in the near to medium term in relatively shallower water and nearer to shore.

In practice, the size of the offshore wind energy resource is, at least theoretically, enormous, and constraints are primarily economic rather than technical. In particular, water depth, accessibility and grid connection may limit development to relatively near-shore locations in the medium term, though technology improvements are expected, over time, to enable deeper water and more remote installations.

Even when only considering relatively shallower and near-shore applications, however, study results span a range from 15 to 130 EJ/yr (4,000 to 37,000 TWh/yr), while far greater technical potential is found when considering deeper water applications that might rely on floating wind turbine designs.

There are two main reasons to believe that some these studies of on- and offshore wind energy may understate the global technical potential. First, several of the studies are dated, and considerable advances have occurred in both wind energy technology (e.g., hub height) and resource assessment methods. Partly as a result, the more recent studies often calculate larger technical potentials than the earlier studies.

Second, even some of the more recent studies may understate the global technical potential for wind energy due to methodological limitations. The global assessments described in this section often use relatively simple analytical techniques with coarse spatial resolutions, rely on interpolations of wind speed data from a limited number (and quality) of surface stations, and apply limited validation from wind speed measurements in prime wind resource areas.

Enabled in part by an increase in computing power, more sophisticated and finer geographic resolution atmospheric modelling approaches are beginning to be applied (and increasingly validated with higher-quality measurement data) on a country or regional basis, as described in more depth. Experience shows that these techniques have often identified greater technical potential for wind energy than have earlier global assessments.

There are, however, at least two other issues that may suggest that the estimates of global technical potential have been overstated. First, global assessments may overstate the accessibility of the wind resource in remote areas that are far from population centres. Second, the assessments generally use point-source estimates of the wind resource, and assess the global technical potential for wind energy by summing local wind technical potentials.

Large-scale atmospheric dynamics, thermodynamic limits, and array effects, however, may bound the aggregate amount of energy that can be extracted by wind farm plants on a regional or global basis. Relatively little is known about the nature of these constraints, though early research suggests that the size of the effects are unlikely to be large enough to significantly constrain the use of wind energy in the electricity sector at a global scale.

Despite the limitations of the available literature, based on the above review, it can be concluded that the IPCC (2007) estimate of 180 EJ/yr (50,000 TWh/yr) likely understates the technical potential for wind energy. Moreover, regardless of the exact size of the technical potential, it is evident that the global wind resource is unlikely to be a limiting factor on global on- or offshore wind energy deployment. Instead, economic constraints associated with the cost of wind energy, institutional constraints and costs associated with transmission access and operational integration, and issues associated with social acceptance and environmental impacts are likely to restrict growth well before any absolute limit to the global technical potential for wind energy is encountered.

Regional technical potential - Global assessment results by region:
The global assessments presented reach varying conclusions about the relative technical potential for onshore wind energy among different regions. Differences in the regional results from these studies are due to differences in wind speed data and key input parameters, including the minimum wind speed assumed to be exploitable, land use constraints, density of wind energy development, and assumed wind farm performance (Hoogwijk et al., 2004); differing regional categories also complicate comparisons. Nonetheless, the technical potentials in OECD North America and Eastern Europe/Eurasia are found to be particularly sizable, whereas some areas of non-OECD Asia andOECD Europe appear to have more limited onshore technical potential. Visual inspection of a global wind resource map with a 5- by 5-km resolution, also demonstrates limited technical potential in certain areas of Latin America and Africa, though other portions of those continents have significant technical potential. Caution is required in interpreting these results, however, as other studies find significantly different regional allocations of global technical potential, and more detailed country and regional assessments have reached differing conclusions about, for example, the wind energy resource in East Asia and other regions.

Hoogwijk et al. (2004) also compare onshore technical potential against regional electricity consumption in 1996. In most of the 17 regions evaluated, technical onshore wind energy potential exceeded electricity consumption in 1996. The multiple was over five in 10 regions: East Africa, Oceania, Canada, North Africa, South America, Former Soviet Union (FSU), Central America, West Africa, the USA and the Middle East.

Areas in which onshore wind energy technical potential was estimated to be less than a two-fold multiple of 1996 electricity consumption were South Asia (1.9), Western Europe (1.6), East Asia (1.1), South Africa (1), Eastern Europe (1), South East Asia (0.1) and Japan (0.1), though again, caution is warranted in interpreting these results.

More recent resource assessments and data on regional electricity consumption would alter these figures. The estimates reported exclude offshore wind energy technical potential. Ignoring deeper water applications, Krewitt et al. (2009) estimate that of the 57 EJ/yr (16,000 TWh/yr) of technical offshore resource potential by 2050, the largest opportunities exist in OECD Europe (22% of global potential), the rest of Asia (21%), Latin America (18%) and the transition economies (16%), with lower but still significant technical potential in North America (12%), OECD Pacific (6%) and Africa and the Middle East (4%).

Overall, these studies find that ample technical potential exists in most regions of the world to enable significant wind energy deployment relative to current levels. The wind resource is not evenly distributed across the globe, however, and a variety of other regional factors (e.g., distance of resource from population centres, grid integration, social acceptance) are likely to restrict growth well before any absolute limit to the technical potential of wind energy is encountered. As a result, wind energy will not contribute equally in meeting the energy needs and GHG reduction demands of every region or country.

Regional assessment results:
The global wind resource assessments described above have historically relied primarily on relatively coarse and imprecise estimates of the wind resource, sometimes relying heavily on measurement stations with relatively poor exposure to the wind (Elliott, 2002; Elliott et al., 2004).

The regional results from these global assessments, should therefore be viewed with some caution, especially in areas where wind measurement data are of limited quantity and quality. In contrast, specific country and regional assessments have benefited from: wind speed data collected with wind resource estimation in mind; sophisticated numerical wind resource prediction techniques; improved model validation; and a dramatic growth in computing power. These advances have allowed the most recent country and regional resource assessments to capture smaller-scale terrain features and temporal variations in predicted wind speeds, and at a variety of possible turbine heights.

These techniques were initially applied in the EU and the USA, but there are now publicly available high-resolution wind resource assessments covering a large number of regions and countries. The United Nations Environment Program’s Solar and Wind Energy Resource Assessment, for example, provides wind resource information for a large number of its partner countries around the world; the European Bank for Reconstruction and Development has developed RE assessments in its countries of operation; the World Bank’s Asia Sustainable and Alternative Energy Program has prepared wind resource atlases for the Pacific Islands and Southeast Asia; and wind resource assessments for portions of the Mediterranean region are available through Observatoire Méditerranéen de l'Energie.

A number of other publicly available country-level assessments have been produced by the US National Renewable Energy Laboratory, Denmark’s Risø DTU and others. These assessments have sometimes proven especially helpful in catalyzing initial interest in wind energy.

These more detailed assessments have generally found the size of the wind resource to be greater than estimated in previous global or regional assessments. This is due primarily to improved data, spatial resolution and analytic techniques, but is also the result of wind turbine technology developments, for example, higher hub heights and improved machine efficiencies.

Nevertheless, even greater spatial and temporal resolution and enhanced validation of model results with observational data are needed, as is an expanded geographic coverage of these assessments. These developments will allow further refinement of estimates of the technical potential, and are likely to highlight regions with high-quality technical potential that have not previously been identified.

Advances in wind resource assessment in China and Russia:
To illustrate the growing use of sophisticated wind resource assessment tools outside of the EU and the USA, historical and ongoing efforts in China and Russia to better characterize their wind resources are described here. In both cases, the wind energy resource has been found to be sizable compared to present electricity consumption, and recent analyses offer enhanced understanding of the size and location of those resources.

China’s Meteorological Administration (CMA) completed its first wind resource assessment in the 1970s. In the 1980s, a second wind resource investigation was performed based on data from roughly 900 meteorological stations, and a spatial distribution of the resource was delineated. The CMA estimated the availability of 253 GW (510 TWh/yr at a 23% average capacity factor; 1.8 EJ/yr) of onshore technical potential (Xue et al., 2001).

A third assessment was based on data from 2,384 meteorological stations, supplemented with data from other sources. Though still mainly based on measured wind speeds at 10 m, most data covered a period of over 50 years, and this assessment led to an estimate of 297 GW (600 TWh/yr at a 23% average capacity factor; 2.2 EJ/yr) of onshore technical potential.

More recently, improved mesoscale atmospheric models and access to higher-elevation meteorological station data have facilitated higher-resolution assessments. The CMA has estimated 2,380 GW of onshore (4,800 TWh/yr at a 23% average capacity factor; 17 EJ/yr) and 200 GW of offshore (610 TWh/yr at a 35% average capacity factor; 2.2 EJ/yr) technical potential (Xiao et al., 2010).

Other recent research has similarly estimated far greater technical potential than have past assessments. Considerable progress has also been made in understanding the magnitude and distribution of the wind energy resource in Russia (as well as the other Commonwealth of Independent States (CIS) countries and the Baltic countries), based in part on data from approximately 3,600 surface meteorological stations and 150 upper-air stations.

An assessment by Nikolaev et al. (2010) uses these data and meteorological and statistical modelling to estimate the distribution of the wind resource in the region. Based on this work and after making assumptions about the characteristics and placement of wind turbines, Nikolaev et al. (2008) estimate that the technical potential for wind energy in Russia is more than 14,000 TWh/yr (50 EJ/yr). The more promising regions of Russia for wind energy development are in the western part of the country, the South Ural area, in western Siberia, and on the coasts of the seas of the Arctic and Pacific Oceans.

Possible impact of climate change on resource potential:
Global climate change may alter the geographic distribution and/or the inter- and intra-annual variability of the wind resource, and/or the quality of the wind resource, and/or the prevalence of extreme weather events that may impact wind turbine design and operation. Research in this field is nascent, however, and global and regional climate models do not fully reproduce contemporary wind climates or historical trends.

Additional uncertainty in wind resource projections under global climate change scenarios derives, in part, from substantial variations in simulated circulation and flow regimes when using different climate models. Nevertheless, research to date suggests that it is unlikely that multi-year annual mean wind speeds will change by more than a maximum of ±25% over most of Europe and North America during the present century, while research covering northern Europe suggests that multi-year annual mean wind power densities will likely remain within ±50% of current values.

Fewer studies have been conducted for other regions of the world, though Brazil’s wind resource was shown in one study to be relatively insensitive to (and perhaps to even increase as a result of) global climate change, and simulations for the west coast of South America showed increases in mean wind speeds of up to 15%.

In addition to the possible impact of climate change on long-term average wind speeds, impacts on intra-annual, interannual and inter-decadal variability in wind speeds are also of interest. Wind climates in northern Europe, for example, exhibit seasonality, with the highest wind speeds during the winter, and some analyses of the northeast Atlantic have found notable differences in temporal trends in winter and summer.

Internal climate modes have been found to be responsible for relatively high intra-annual, interannual and inter-decadal variability in wind climates in the mid-latitudes. The ability of climate models to accurately reproduce these conditions in current and possible future climates is the subject of intense research.

Equally, the degree to which historical variability and change in near-surface wind climates is attributable to global climate change or to other factors, and whether that variability will change as the global climate continues to evolve, is also being investigated.

Finally, the prevalence of extreme winds and the probability of icing have implications for wind turbine design and operation. Preliminary studies from northern and central Europe show some evidence of increased wind speed extremes, though changes in the occurrence of inherently rare events are difficult to quantify, and further research is warranted. Sea ice can impact turbine foundation
loading for offshore wind farm plants, and changes in sea ice and/or permafrost conditions may also influence access for performing wind power plant O&M.

Additional research on the possible impact of climate change on the size, geographic distribution and variability of the wind resource is warranted, as is research on the possible impact of climate change on extreme weather events and therefore wind turbine operating environments. Overall, however, research to date suggests that these impacts are unlikely to be of a magnitude that will greatly impact the global potential of wind energy deployment.

Please refer to http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch07 for the full report

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