TODAY’S STUDY: ALL NEW ENERGY BY 2030 (Part 1)

Opponents of New Energy constantly take the "reasonable" position that they would be be happy to rely on it if only there were enough. They have been impeding the growth of New Energy with this argument since the 1970s. If they had been building New Energy since the 1970s, there would now be plenty of it and such an argument wouldn't be reasonable.

This "reasonable" argument will become yet more familiar in the U.S. during the next 2 years as conservatives who side with the opponents of New Energy exert their newly won influence in Congress.

Two scholars at Stanford University - not a place known for shabby-thinking faculty members - have, for the last couple of years, been doing carefully researched and referenced studies (like the one highlighted below) showing that the U.S. and the world can move to an energy system based 100% on New Energy and completely eliminate the use of the toxic Old Energies (coal, oil, natural gas and nuclear).

Turns out it is a perfectly reasonable position. (Part II tomorrow).

Providing all global energy with wind, water, and solar power, Part I: Technologies, energy resources, quantities and areas of infrastructure, and materials
Mark Z.Jacobson and Mark A. Delucchi, November 2010 (Stanford University via Science Direct)

Abstract

Climate change, pollution, and energy insecurity are among the greatest problems of our time. Addressing them requires major changes in our energy infrastructure. Here, we analyze the feasibility of providing worldwide energy for all purposes (electric power, transportation, heating/cooling, etc.) from wind, water, and sunlight (WWS). In Part I, we discuss WWS energy system characteristics, current and future energy demand, availability of WWS resources, numbers of WWS devices, and area and material requirements. In Part II, we address variability, economics, and policy of WWS energy. We estimate that !3,800,000 5 MW wind turbines, !49,000 300 MW concentrated solar plants, !40,000 300 MW solar PV power plants, !1.7 billion 3 kWrooftop PV systems, !5350 100 MWgeothermal power plants, !270 new 1300 MWhydroelectric power plants, !720,000 0.75 MWwave devices, and !490,000 1 Mwtidal turbines can power a 2030 WWS world that uses electricity and electrolytic hydrogen for all purposes. Such a WWS infrastructure reduces world power demand by 30% and requires only !0.41% and !0.59% more of the world’s land for footprint and spacing, respectively. We suggest producing all new energy withWWSby 2030 and replacing the pre-existing energy by 2050. Barriers to the plan are primarily social and political, not technological or economic. The energy cost in a WWS world should be similar to that today.

Introduction

A solution to the problems of climate change, air pollution, water pollution, and energy insecurity requires a large-scale conversion to clean, perpetual, and reliable energy at low cost together with an increase in energy efficiency. Over the past decade, a number of studies have proposed large-scale renewable energy plans. Jacobson and Masters (2001) suggested that the U.S. could satisfy its Kyoto Protocol requirement for reducing carbon dioxide emissions by replacing 60% of its coal generation with 214,000–236,000 wind turbines rated at 1.5MW (million watts). Also in 2001, Czisch (2006) suggested that a totally renewable electricity supply system, with intercontinental transmission lines linking dispersed wind sites with hydropower backup, could supply Europe, North Africa, and East Asia at total costs per kWh comparablewith the costs of the current system.Hoffert et al. (2002) suggested a portfolio of solutions for stabilizing atmospheric CO2, including increasing the use of renewable energy and nuclear energy, decarbonizing fossil fuels and sequestering carbon, and improving energy efficiency. Pacala and Socolow (2004) suggested a similar portfolio, but expanded it to include reductions in deforestation and conservation tillage and greater use of hydrogen in vehicles.

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More recently, Fthenakis et al. (2009) analyzed the technical, geographical, and economic feasibility for solar energy to supply the energy needs of the U.S. and concluded (p. 397) that ‘‘it is clearly feasible to replace the present fossil fuel energy infrastructure in the U.S. with solar power and other renewables, and reduce CO2 emissions to a level commensurate with the most aggressive climate-change goals’’. Jacobson (2009) evaluated several long-term energy systems according to environmental and other criteria, and found WWS systems to be superior to nuclear, fossil-fuel, and biofuel systems (see further discussion in Section 2). He proposed to address the hourly and seasonal variability of WWS power by interconnecting geographically disperse renewable energy sources to smooth out loads, using hydroelectric power to fill in gaps in supply. He also proposed using battery-electric vehicles (BEVs) together with utility controls of electricity dispatch to them through smart meters, and storing electricity in hydrogen or solar-thermal storage media. Cleetus et al. (2009) subsequently presented a ‘‘blueprint’’ for a clean-energy economy to reduce CO2-equivalent GHG emissions in the U.S. by 56% compared with the 2005 levels. That study featured an economy-wide CO2 cap-and-trade program and policies to increase energy efficiency and the use of renewable energy in industry, buildings, electricity, and transportation. Sovacool and Watts (2009) suggested that a completely renewable electricity sector for New Zealand and the United States is feasible.

In Jacobson and Delucchi (2009), we outlined a large-scale plan to power the world for all purposes withWWS(no biofuels, nuclear power, or coal with carbon capture). The study found that it was technically feasible to power the world with WWS by 2030 but such a conversion would almost certainly take longer due to the difficulty in implementing all necessary policies by then. However, we suggested, and this study reinforces, the concept that all new energy could be supplied by WWS by 2030 and all existing energy could be converted toWWSby 2050. The analysis presented here is an extension of that work…

More well known to the public than the scientific studies, perhaps, are the ‘‘Repower America’’ plan of former Vice-President and Nobel-Peace Prize winner Al Gore, and a similar proposal by businessman T. Boone Pickens. Mr. Gore’s proposal calls for improvements in energy efficiency, expansion of renewable energy generation, modernization of the transmission grid, and the conversion of motor vehicles to electric power. The ultimate (and ambitious) goal is to provide America ‘‘with 100% clean electricity within 10 years,’’ which Mr. Gore proposes to achieve by increasing the use of wind and concentrated solar and improving energy efficiency (Alliance for Climate Protection, 2009). In Gore’s plan,solar PV, geothermal, and biomass electricity would grow only modestly, and nuclear power and hydroelectricity would not grow. Mr. Pickens’ plan is to obtain up to 22% of the U.S. electricity from wind, add solar capacity to that, improve the electric grid, increase energy efficiency, and use natural gas instead of oil as a transitional fuel (Pickens, 2009).

There is little doubt that the large-scale use of renewable energy envisaged in these plans and studies would greatly mitigate or eliminate a wide range of environmental and human health impacts of energy use (e.g., Jacobson, 2009; Sovacool and Sovacool, 2009; Colby et al., 2009; Weisser, 2007; Fthenakis and Kim, 2007). But, is a large-scale transformation of the world’s energy systems feasible? In this paper and in Part II, we address this question by examining the characteristics and benefits of wind, water, and solar (WWS)-energy systems, the availability of WWS resources, supplies of critical materials, methods of addressing the variability of WWS energy to ensure that power supply reliably matches demand, the economics ofWWSgeneration and transmission, the economics of the use ofWWSpower in transportation, and policy issues. Although we recognize that a comprehensive plan to address global environmental problems must also address other sectors, including agriculture (Horrigan et al., 2002; Wall and Smit, 2005) and forestry (Niles et al., 2002), we do not address those issues here.

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Clean, low-risk, sustainable energy systems

Evaluation of long-term energy systems: why we choose WWS power

Because climate change (particularly loss of the Arctic sea ice cap), air pollution, and energy insecurity are the current and growing problems, but it takes several decades for new technologies to become fully adopted, we consider only options that have been demonstrated in at least pilot projects and that can be scaled up as part of a global energy system without further major technology development. We avoid options that require substantial further technological development and that will not be ready to begin the scale-up process for several decades. Note that we select technologies based on the state of development of the technology only rather than whether industrial capacity is currently ramped up to produce the technologies on a massive scale or whether society is motivated to change to the technologies. In this paper and in Part II, we do consider the feasibility of implementing the chosen technologies based on estimated costs, necessary policies, and available materials as well as other factors.

In order to ensure that our energy system remains clean even with large increases in population and economic activity in the long run, we consider only those technologies that have essentially zero emissions of greenhouse gases and air pollutants per unit of output over the whole ‘‘lifecycle’’ of the system. Similarly, we consider only those technologies that have low impacts on wildlife, water pollution, and land, do not have significant waste-disposal or terrorism risks associated with them, and are based on primary resources that are indefinitely renewable or recyclable.

The previous work by Jacobson (2009) indicates that WWS power satisfies all of these criteria. He ranked several long-term energy systems with respect to their impacts on global warming, air pollution, water supply, land use, wildlife, thermal pollution, water–chemical pollution, and nuclear weapons proliferation. The ranking of electricity options, starting with the highest, included: wind power, concentrated solar, geothermal, tidal, solar photovoltaic, wave, and hydroelectric power, all of which are powered by wind, water, or sunlight (WWS). He also found that the use of BEVs and hydrogen fuel-cell vehicles (HFCVs) powered by the WWS options would largely eliminate pollution from the transportation sector. Here, we consider these technologies and other existing technologies for the heating/cooling sectors, discussed in

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Although other clean WWS electric power sources, such as ocean or river current power, could be deployed in the short term, these are not examined here simply because we could not cover every technology. Nevertheless, we do cover related although slightly different power sources (e.g., wave, tidal, and hydroelectric power).

Finally, Jacobson (2009) concluded that coal with carbon capture, corn ethanol, cellulosic ethanol, and nuclear power were all moderately or significantly worse than WWS options with respect to environmental and land use impacts. Similarly, here we do not consider any combustion sources, such as coal with carbon capture, corn ethanol, cellulosic ethanol, soy biodiesel, algae biodiesel, biomass for electricity, other biofuels, or natural gas, because none of these technologies can reduce GHG and air-pollutant emissions to near zero, and all can have significant problems in terms of land use, water use, or resource availability (See Delucchi (2010) for a review of land-use, climate-change, and
water-use impacts of biofuels.) For example, even the most climate-friendly and ecologically acceptable sources of ethanol, such as unmanaged, mixed grasses restored to their native (nonagricultural) habitat (Tilman et al., 2006), will cause air pollution mortality on the same order as gasoline (Jacobson, 2007; Anderson, 2009; Ginnebaugh et al., 2010). The use of carbon capture and sequestration (CCS) can reduce CO2 emissions from the stacks of coal power plants by 85–90% or more, but it has no effect on CO2 emissions due to the mining and transport of coal; in fact it will increase such emissions and of air pollutants per unit of net delivered power and will increase all ecological, land-use, air-pollution, and water-pollution impacts from coal mining, transport, and processing, because the CCS system requires 25% more energy, thus 25% more coal combustion, than does a system without CCS (IPCC, 2005).

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For several reasons we do not consider nuclear energy (conventional fission, breeder reactors, or fusion) as a long-term global energy source. First, the growth of nuclear energy has historically increased the ability of nations to obtain or enrich uranium for nuclear weapons (Ullom, 1994), and a large-scale worldwide increase in nuclear energy facilities would exacerbate this problem, putting the world at greater risk of a nuclear war or terrorism catastrophe (Kessides, 2010; Feiveson, 2009; Miller and Sagan, 2009; Macfarlane and Miller, 2007; Harding, 2007)…

Second, nuclear energy results in 9–25 times more carbon emissions than wind energy, in part due to emissions from uranium refining and transport and reactor construction (e.g., Lenzen, 2008; Sovacool, 2008), in part due to the longer time required to site, permit, and construct a nuclear plant compared with a wind farm (resulting in greater emissions from the fossil-fuel electricity sector during this period; Jacobson, 2009), and in part due to the greater loss of soil carbon due to the greater loss in vegetation resulting from covering the ground with nuclear facilities relative to wind turbine towers, which cover little ground. Although recent construction times worldwide are shorter than the 9-year median construction times in the U.S. since 1970 (Koomey and Hultman, 2007), they still averaged 6.5 years worldwide in 2007 (Ramana, 2009), and this time must be added to the site permit time (!3 years in the U.S.) and construction permit and issue time (!3 years). The overall historic and present range of nuclear planning-to-operation times for new nuclear plants has been 11–19 years, compared with an average of 2–5 years for wind and solar installations (Jacobson, 2009)…

Third, conventional nuclear fission relies on finite stores of uranium that a large-scale nuclear program with a ‘‘once through’’ fuel cycle would exhaust in roughly a century (e.g., Macfarlane and Miller, 2007; Adamantiades and Kessides, 2009). In addition, accidents at nuclear power plants have been either catastrophic (Chernobyl) or damaging (Three-Mile Island), and although the nuclear industry has improved the safety and performance of reactors, and has proposed new (but generally untested) ‘‘inherently’’ safe reactor designs (Piera, 2010; Penner et al., 2008; Adamantiades and Kessides, 2009; Mourogov et al., 2002; Mourogov, 2000), there is no guarantee that the reactors will be designed, built, and operated correctly… ‘‘Breeder’’ nuclear reactors have similar problems as conventional fission reactors, except that they produce less low-level radioactive waste…

A related proposal is to use thorium as a nuclear fuel, which is less likely to lead to nuclear weapons proliferation than the use of uranium, produces less long-lived radioactive waste, and greatly extends uranium resources (Macfarlane and Miller, 2007). However, thorium reactors require the same significant time lag between planning and operation as conventional uranium reactors and most likely longer because few developers and scientists have experience with constructing or running thorium reactors. As such, this technology will result in greater emissions from the background electric grid compared with WWS technologies…

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Fusion of light atomic nuclei (e.g., protium, deuterium, or tritium) theoretically could supply power indefinitely without long-lived radioactive wastes as the products are isotopes of helium (Ongena and Van Oost, 2006; Tokimatsu et al., 2003); however, it would produce short-lived waste that needs to be removed from the reactor core to avoid interference with operations, and it is unlikely to be commercially available for at least another 50–100 years (Tokimatsu et al., 2003; Barre´ , 1999; Hammond, 1996), long after we will have needed to transition to alternative energy sources. By contrast, wind and solar power are available today, will last indefinitely, and pose no serious risks…

For these reasons, we focus on WWS technologies. We assume thatWWSwill supply electric power for the transportation, heating (including high-temperature heating and cooking)/cooling sectors, which traditionally have relied mainly on the direct use of oil or gas rather than electricity, as well as for traditional electricity-consuming end uses such as lighting, cooling, manufacturing, motors, electronics, and telecommunications. Although we focus mainly on energy supply, we acknowledge and indeed emphasize the importance of demand-side energy conservation measures to reduce the requirements and impacts of energy supply. Demand-side energy conservation measures include improving the energy-out/energy in efficiency of end uses (e.g., with more efficient vehicles, more efficient lighting, better insulation in homes, and the use of heat exchange and filtration systems), directing demand to low-energy use modes (e.g., using public transit or telecommuting instead of driving), large-scale planning to reduce energy demand without compromising economic activity or comfort (e.g., designing cities to facilitate greater use of non-motorized transport and to have better matching of origins and destinations, thereby reducing the need for travel), and designing buildings to use solar energy directly (e.g., with more daylighting, solar hot water heating, and improved passive solar heating in winter and cooling in summer). For a general discussion of the potential to reduce energy use in transportation and buildings, see the American Physical Society (2008). For a classification scheme that facilitates analyses of the potential gains from energy efficiency, see Cullen and Allwood (2009).

Characteristics of electricity-generating WWS technologies

Wind

Wind turbines convert the energy of the wind into electricity. Generally, a gearbox turns the slow-moving turbine rotor into faster-rotating gears, which convert mechanical energy to electricity in a generator. Some modern turbines are gearless. Although less efficient, small turbines can be used in homes or buildings. Wind farms today appear on land and offshore, with individual turbines ranging in size up to 7 MW, with 10MW planned. High-altitude wind energy capture is also being pursued today by several companies.

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Wave

Winds passing over water create surface waves. The faster the wind speed, the longer the wind is sustained, the greater the distance the wind travels, the greater the wave height, and the greater the wave energy produced. Wave power devices capture energy from ocean surface waves to produce electricity. One type of device is a buoy that rises and falls with a wave. Another type is a surface-following device, whose up-and-down motion increases the pressure on oil to drive a hydraulic motor.

Geothermal

Steam and hot water from below the Earth’s surface have been used historically to provide heat for buildings, industrial processes, and domestic water and to generate electricity in geothermal power plants. In power plants, two boreholes are drilled—one for steam alone or liquid water plus steam to flow up, and the second for condensed water to return after it passes through the plant. In some plants, steam drives a turbine; in others, hot water heats another fluid that evaporates and drives the turbine.

Hydroelectricity

Water generates electricity when it drops gravitationally, driving a turbine and generator. While most hydroelectricity is produced by water falling from dams, some is produced by water flowing down rivers (run-of-the-river electricity).

Tidal

A tidal turbine is similar to a wind turbine in that it consists of a rotor that turns due to its interaction with water during the ebb and flow of a tide. Tidal turbines are generally mounted on the sea floor. Since tides run about 6 h in one direction before switching directions for 6 h, tidal turbines can provide a predictable energy source. O’Rourke et al. (2010) provide an excellent overview of the technology of tidal energy.

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Solar PV

Solar photovoltaics (PVs) are arrays of cells containing a material, such as silicon, that converts solar radiation into electricity. Today, solar PVs are used in a wide range of applications, from residential rooftop power generation to medium-scale utility level power generation.

CSP

Concentrated solar power (CSP) systems use mirrors or reflective lenses to focus sunlight on a fluid to heat it to a high temperature. The heated fluid flows from the collector to a heat engine where a portion of the heat is converted to electricity. Some types of CSP allow the heat to be stored for many hours so that electricity can be produced at night.

Use of WWS power for transportation

Transportation technologies that must be deployed on a large scale to use WWS-power include primarily battery-electric vehicles (BEVs), hydrogen fuel-cell vehicles (HFCVs), and hybrid BEV-HFCVs. For ships, we propose the use of hybrid hydrogen fuel cell-battery systems, and for aircraft, liquefied hydrogen combustion (Appendix A).

BEVs store electricity in and draw power from batteries to run an electricmotor that drives the vehicle. So long as the electricity source is clean, the BEV systemwill have zero emissions of air pollutants and greenhouse gases over the entire energy lifecycle—something that internal-combustion-engine vehicles (ICEVs)using liquidfuels cannot achieve.Moreover, BEVs provide up to 5 timesmorework in distance traveled per unit of input energy than do ICEVs (km/kWh-outlet versus km/kWh-gasoline). BEVs have existed for decades in small levels of production, but todaymostmajor automobile companies are developing BEVs. The latest generation of vehicles uses lithium-ion batteries, which do not use the toxic chemicals associated with lead acid or the nickel-cadmium batteries.

Hydrogen fuel cell vehicles (HFCVs) use a fuel cell to convert hydrogen fuel and oxygen from the air into electricity that is used to run an electric motor. HFCVs are truly clean only if the hydrogen is produced by passing WWS-derived electricity through water (electrolysis). Thus, we propose producing hydrogen only in this way. Several companies have prototype HFCVs, and California had about 200 HFCVs on the road in 2009 (California Fuel Cell Partnership, 2009). Hydrogen fueling stations, though, are practically non-existent and most hydrogen today is produced by steam reforming of natural gas, which is not so clean as hydrogen produced by WWS-electrolysis.

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Use of WWS power for heating and cooling

For building water and air heating using WWS power, we propose the use of air- and ground-source heat-pump water and air heaters and electric resistance water and air heaters. Heat pump air heaters also can be used in reverse for air conditioning. These technologies exist today although in most places they satisfy less demand than do natural gas or oil-fired heaters. The use of electricity for heating and cooking, like the use of electricity for transportation, is most beneficial when the electricity comes from WWS. For high-temperature industrial processes, we propose that energy be obtained by combustion of electrolytic hydrogen (Appendix A).

Energy resources needed and available

The power required today to satisfy all end uses worldwide is about 12.5 trillion watts (TW) (EIA, 2008a; end-use energy only, excludes losses in production and transmission). In terms of primary energy, about 35% is from oil, 27% from coal, 23% from natural gas, 6% from nuclear, and the rest from biomass, sunlight, wind, and geothermal. Delivered electricity is a little over 2 TW of the end-use total.

The EIA (2008a) projects that in the year 2030, the world will require almost 17 TW in end-use power, and the U.S. almost 3 TW (Table 2). They also project that the breakdown in terms of primary energy in 2030 will be similar to that today—heavily dependent on fossil fuels, and hence almost certainly unsustainable. What would world power demand look like if instead a sustainable WWS system supplied all end-use energy needs?

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Table 2 shows our estimates of global and U.S. end-use energy demand, by sector, in a world powered entirely by WWS, with zero fossil-fuel and biomass combustion. We have assumed that all end uses that feasibly can be electrified use WWS power directly, and that the remaining end uses useWWSpower indirectly in the form of electrolytic hydrogen (hydrogen produced by splitting water with WWS power). As explained in Section 2 we assume that most uses of fossil fuels for heating/cooling can be replaced by electric heat pumps, and that most uses of liquid fuels for transportation can be replaced by BEVs. The remaining, non-electric uses can be supplied by hydrogen, which we assume would be compressed for use in fuel cells in remaining non-aviation transportation, liquefied and combusted in aviation, and combusted to provide heat directly in the industrial sector. The hydrogen would be produced using WWS power to split water; thus, directly or indirectly, WWS powers the world.

As shown in Table 2, the direct use of electricity, for example, for heating or electric motors, is considerably more efficient than is fuel combustion in the same application. The use of electrolytic hydrogen is less efficient than is the use of fossil fuels for direct heating but more efficient for transportation when fuel cells are used; the efficiency difference between direct use of electricity and electrolytic hydrogen is due to the energy losses of electrolysis, and in the case of most transportation uses, the energy requirements of compression and the greater inefficiencies of fuel cells than batteries. Assuming that some additional modest energy-conservation measures are implemented (see the list of demand-side conservation measures in Section 2) and subtracting the energy requirements of petroleum refining, we estimate that an all-WWS world would require !30% less end-use power than the EIA projects for the conventional fossil-fuel scenario (Table 1).

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How do the energy requirements of a WWS world, shown in Table 2, compare with the availability ofWWSpower? Table 3 gives the estimated power available worldwide from renewable energy, in terms of raw resources, resources available in high-energy locations, resources that can feasibly be extracted in the near term considering cost and location, and the current resources used. The table indicates that only solar and wind can provide more power on their own than energy demand worldwide. Wind in developable locations can power the world about 3–5 times over and solar, about 15–20 times over.

Fig. 1 shows the modeled world wind resources at 100 m, in the range of the hub height of modern wind turbines. Globally, !1700 TW of wind energy are available over the world’s land plus ocean surfaces at 100 m if all wind at all speeds were used to power wind turbines (Table 3); however, the wind power over land in locations over land and near shore where the wind speed is 7 m/s or faster (the speed necessary for cost-competitive wind energy) is around 72–170 TW (Archer and Jacobson, 2005; Lu et al., 2009; Fig. 1). Over half of this power is in locations that could practically be developed. Large regions of fast winds worldwide include the Great Plains of the U.S. and Canada, Northern Europe, the Gobi and Sahara Deserts, much of the Australian desert areas, and parts of South Africa and Southern South America and South Africa. In the U.S., wind from the Great Plains and offshore the East Coast (Kempton et al., 2007) could supply all U.S. energy needs. Other windy offshore regions include the North Sea, the West Coast of the U.S. (Dvorak et al., 2010), and the East Coast of Asia among others.

Extraction from the wind of 100% of the power needed for the world in 2030 (11.5 TW from Table 2) would reduce the overall power in the wind at 100 m by o1% (Santa Maria and Jacobson, 2009). Such extracted power is eventually dissipated to heat, a portion of which is cycled back to produce more potential energy, which produces kinetic energy, regenerating some of the wind. The remaining heat goes toward slightly increasing air and ground temperature, but this addition is very small. For example, the maximum additional radiative forcing due to powering the world with wind is !11.5 TW/5.106#1014 m2 (area of the Earth)¼0.022 W/m2, which is only !0.7% of the !3 W/m2 forcing due to all greenhouse gases. Since wind turbines replace other electricity sources that also produce heat in this manner (Santa Maria and Jacobson, 2009), wind turbines (and other renewable electricity sources) replacing current infrastructure cause no net heat addition to the atmosphere. They serve only to reduce global-warming pollutants and heath-affecting air pollutants that current electricity and energy sources produce.

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Fig. 2 shows the distribution of solar energy at the Earth’s surface. Globally, 6500 TW of solar energy are available over the world’s land plus ocean surfaces if all sunlight is used to power photovoltaics (Table 3); however, the deliverable solar power over land in locations where solar PV could practically be developed is about 340 TW. Alternatively CSP could provide about 240 TWof the world’s power output, less than PV since the land area required for CSP without storage is about one-third greater than is that for PV. With thermal storage, the land area for CSP increases since more solar collectors are needed to provide energy for storage, but energy output does not change and the energy can be used at night. However, water-cooled CSP plants can require water for cooling during operation (about 8 gal/kWh—much more than PVs and wind (!0 gal/kWh), but less than nuclear and coal (!40 gal/kWh) (Sovacool and Sovacool, 2009)), and this might be a constraint in some areas. This constraint is not accounted for in the estimates of Table 3. However, air-cooled CSP plants require over 90% less water than water-cooled plants at the cost of only about 5% less electric power and 2–9% higher electricity rates (USDOE, 2008b), suggesting air-cooled plants may be a viable alternative in water limited locations.

The other WWS technologies have much less resource availability than do wind, CSP, and PV (Table 3), yet can still contribute beneficially to the WWS solution. Wave power can be extracted practically only near coastal areas, which limits its worldwide potential. Although the Earth has a very large reservoir of geothermal energy below the surface, most of it is too deep to extract practically. Even though hydroelectric power today exceeds all other sources ofWWSpower, its future potential is limited because most of the large reservoirs suitable for generating hydropower are already in use.

Further, although there is enough feasibly developable wind and solar power to supply the world, other WWS resources will be more abundant and more economical than wind and solar in many locations. Finally, wind and solar power are variable, so geothermal and tidal power, which provide relatively constant power, and hydroelectric, which fills in gaps, will be important for providing a stable electric power supply…

Part II tomorrow.