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2010/12/28-By 2050 Solar Power Could End U.S. Dependence on Foreign Oil and Slash Greenhouse Gas Emissions

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BIG IDEAS By 2050 solar power could end U.S. dependence on foreign oil and slash greenhouse gas emissions By Ken Zweibel, James Mason and Vasilis Fthenakis H

igh prices for gasoline and home heating oil are here to stay.

The U.S. is at war in the Middle East at least in part to protect its foreign oil interests. And as China, India and other nations rapidly increase their demand for fossil fuels, future "ghting over energy looms large. In the meantime, power plants that burn coal, oil and natural gas, as well as vehicles everywhere, continue to pour millions of tons of pollutants and greenhouse gases into the atmo-sphere annually, threatening the planet.

Well-meaning scientists, engineers, economists and politicians have proposed various steps that could slightly reduce fossil-fuel use and emissions. These steps are not enough. The U.S. needs a bold plan to free itself from fossil fuels. Our analysis convinces us that a KEY CONCEPTS massive switch to solar power is the logical answer.

Solar energys potential is off the chart. The energy in sunlight A massive switch from coal, oil, natural gas and striking the earth for 40 minutes is equivalent to global energy con-nuclear power plants to so- sumption for a year. The U.S. is lucky to be endowed with a vast re-lar power plants could sup- source; at least 250,000 square miles of land in the Southwest alone ply 69 percent of the U.S.s are suitable for constructing solar power plants, and that land receives electricity and 35 percent more than 4,500 quadrillion British thermal units (Btu) of solar ra-of its total energy by 2050. diation a year. Converting only 2.5 percent of that radiation into elec-A vast area of photovoltaic tricity would match the nations total energy consumption in 2006.

cells would have to be To convert the country to solar power, huge tracts of land would erected in the Southwest. have to be covered with photovoltaic panels and solar heating Excess daytime energy troughs. A direct-current (DC) transmission backbone would also would be stored as com- have to be erected to send that energy ef"ciently across the nation.

pressed air in underground The technology is ready. On the following pages we present a caverns to be tapped dur- grand plan that could provide 69 percent of the U.S.s electricity and ing nighttime hours.

35 percent of its total energy (which includes transportation) with Large solar concentrator solar power by 2050. We project that this energy could be sold to power plants would be consumers at rates equivalent to todays rates for conventional pow-built as well. er sources, about "ve cents per kilowatt-hour (kWh). If wind, bio-A new direct-current pow- mass and geothermal sources were also developed, renewable ener-er transmission backbone gy could provide 100 percent of the nations electricity and 90 per-SCHOTT AG/COMMERCIAL HANDOUT/EPA/CORBIS would deliver solar elec- cent of its energy by 2100.

tricity across the country. The federal government would have to invest more than $400 bil-lion over the next 40 years to complete the 2050 plan. That invest-A But $420 billion in subsi-dies from 2011 to 2050 ment is substantial, but the payoff is greater. Solar plants consume would be required to fund little or no fuel, saving billions of dollars year after year. The infra-the infrastructure and structure would displace 300 large coal-"red power plants and 300 make it cost-competitive. more large natural gas plants and all the fuels they consume. The The Editors plan would effectively eliminate all imported oil, fundamentally cut-ting U.S. trade de"cits and easing political tension in the Middle East 64 SCIENTIFIC AMERICAN

Solar Grand Plan and elsewhere. Because solar technologies are almost pollution-free, the plan would also re- U.S. Plan for 2050 TECHNOLOGY duce greenhouse gas emissions from power plants by 1.7 billion tons a year, and another 1.9 PHOTOVOLTAICS billion tons from gasoline vehicles would be dis- Solar Power Provides . . .

placed by plug-in hybrids refueled by the solar power grid. In 2050 U.S. carbon dioxide emis-sions would be 62 percent below 2005 levels, 69%

of electricity 35%

of total energy putting a major brake on global warming.

Photovoltaic Farms In the past few years the cost to produce photo-voltaic cells and modules has dropped signi"-

B y 2050 vast photovoltaic arrays in the Southwest would supply electricity instead of fossil-fueled power plants and would also power a widespread conversion to plug-in electric vehi-COMPRESSED-AIR ENERGY STORAGE cantly, opening the way for large-scale deploy- (with photovoltaic cles. Excess energy would be stored as compressed air in under-ment. Various cell types exist, but the least expen- electricity) ground caverns. Large arrays that concentrate sunlight to heat sive modules today are thin films made of water would also supply electricity. A new high-voltage, direct-cur-cadmium telluride. To provide electricity at six rent transmission backbone would carry power to regional markets cents per kWh by 2020, cadmium telluride mod- CONCENTRATED nationwide. The technologies and factors critical to their success ules would have to convert electricity with 14 SOLAR POWER are summarized at the right, along with the extent to which the percent ef"ciency, and systems would have to be technologies must be deployed by 2050. The plan would substan-installed at $1.20 per watt of capacity. Current tially cut the countrys consumption of fossil fuels and its emission modules have 10 percent efficiency and an of greenhouse gases (below). We have assumed a 1 percent annual installed system cost of about $4 per watt. Prog- growth in net energy demand. And we have anticipated improve-ress is clearly needed, but the technology is ments in solar technologies forecasted only until 2020, with no fur-advancing quickly; commercial ef"ciencies have ther gains beyond that date. K.Z., J.M. and V.F. DC TRANSMISSION risen from 9 to 10 percent in the past 12 months.

It is worth noting, too, that as modules improve, rooftop photovoltaics will become more cost-competitive for homeowners, reducing daytime electricity demand.

In our plan, by 2050 photovoltaic technology ANNUAL U.S. FUEL CONSUMPTION would provide almost 3,000 gigawatts (GW), or 2007 billions of watts, of power. Some 30,000 square ANNUAL U.S. FUEL CONSUMPTION 2050 (Existing energy path) miles of photovoltaic arrays would have to be 2007 2050 (Solar grand plan) erected. Although this area may sound enor- 2050 (Existing energy path) mous, installations already in place indicate that OIL2050 (Solar grand plan) 6.9 10.9 2.7 the land required for each gigawatt-hour of so- Billion barrels OIL lar energy produced in the Southwest is less than 6.9 10.9 2.7 Billion barrels that needed for a coal-powered plant when fac-JEN CHRISTIANSEN (graph); KENN BROWN AND CHRIS WREN Mondolithic Studios (illustration) toring in land for coal mining. Studies by the NATURAL GAS National Renewable Energy Laboratory in 22.2 35.4 11.4 Trillion cubic feet Golden, Colo., show that more than enough NATURAL GAS 22.2 35.4 11.4 land in the Southwest is available without re- Trillion cubic feet quiring use of environmentally sensitive areas, population centers or difficult terrain. Jack COAL 1.2 1.9 0.5 Lavelle, a spokesperson for Arizonas Depart- Billion tons COAL ment of Water Conservation, has noted that 1.2 1.9 0.5 Billion tons more than 80 percent of his states land is not privately owned and that Arizona is very inter- U.S. EMISSIONS ested in developing its solar potential. The be-CARBON U.S. DIOXIDE EMISSIONS nign nature of photovoltaic plants (including no 6.1 9.4 2.3 Billion tons water consumption) should keep environmental CARBON DIOXIDE 6.1 9.4 2.3 concerns to a minimum. Billion tons The main progress required, then, is to raise module ef"ciency to 14 percent. Although the 66 SCIENTIFIC AMERICAN

CRITICAL FACTOR 2007 2050 ADVANCES NEEDED Land area 10 sq miles 30,000 sq miles Policies to develop large public land areas Thin-"lm module ef"ciency 10% 14% More transparent materials to improve light transmission; more densely doped layers to increase voltage; larger modules to reduce inactive area Installed cost $4/W $1.20/W Improvements in module ef"ciency; gains from volume production Electricity price 16¢/kWh 5¢/kWh Follows from lower installed cost Total capacity 0.5 GW 2,940 GW National energy plan built around solar power Volume 0 535 billion cu ft Coordination of site development with natural gas industry Installed cost $5.80/W $3.90/W Economies of scale; decreasing photovoltaic electricity prices Electricity price 20¢/kWh 9¢/kWh Follows from lower installed cost Total capacity 0.1 GW 558 GW National energy plan Land area 10 sq miles 16,000 sq miles Policies to develop large public land areas Solar-to-electric ef"ciency 13% 17% Fluids that transfer heat more effectively Installed cost $5.30/W $3.70/W Single-tank thermal storage systems; economies of scale Electricity price 18¢/kWh 9¢/kWh Follows from lower installed cost Total capacity 0.5 GW 558 GW National energy plan Length 500 miles 100,000- New high-voltage DC grid from Southwest to rest of country 500,000 miles

By 2100 ef"ciencies of commercial modules will never reach those of solar cells in the laboratory, cad-they would if they were fueled by natural gas alone, and better heat recovery technology renewable mium telluride cells at the National Renewable would lower that "gure to 30 percent.

energy could Energy Laboratory are now up to 16.5 percent and rising. At least one manufacturer, First So-Studies by the Electric Power Research Insti-tute in Palo Alto, Calif., indicate that the cost generate lar in Perrysburg, Ohio, increased module ef"- of compressed-air energy storage today is about 100 percent ciency from 6 to 10 percent from 2005 to 2007 and is reaching for 11.5 percent by 2010.

half that of lead-acid batteries. The research in-dicates that these facilities would add three or of the U.S.s four cents per kWh to photovoltaic generation, electricity and Pressurized Caverns bringing the total 2020 cost to eight or nine The great limiting factor of solar power, of cents per kWh.

more than course, is that it generates little electricity when Electricity from photovoltaic farms in the 90 percent of skies are cloudy and none at night. Excess pow-er must therefore be produced during sunny Southwest would be sent over high-voltage DC transmission lines to compressed-air storage its energy. hours and stored for use during dark hours. facilities throughout the country, where tur-Most energy storage systems such as batteries bines would generate electricity year-round.

are expensive or inef"cient. The key is to "nd adequate sites. Mapping by Compressed-air energy storage has emerged the natural gas industry and the Electric Power as a successful alternative. Electricity from pho- Research Institute shows that suitable geologic tovoltaic plants compresses air and pumps it formations exist in 75 percent of the country, into vacant underground caverns, abandoned often close to metropolitan areas. Indeed, a mines, aquifers and depleted natural gas wells. compressed-air energy storage system would TUCSON ELECTRIC POWER COMPANY The pressurized air is released on demand to look similar to the U.S. natural gas storage sys-turn a turbine that generates electricity, aided by tem. The industry stores eight trillion cubic feet burning small amounts of natural gas. Com- of gas in 400 underground reservoirs. By 2050 pressed-air energy storage plants have been op- our plan would require 535 billion cubic feet of erating reliably in Huntorf, Germany, since storage, with air pressurized at 1,100 pounds 1978 and in McIntosh, Ala., since 1991. The tur- per square inch. Although development will be bines burn only 40 percent of the natural gas a challenge, plenty of reservoirs are available, Photovoltaics In the 2050 plan vast photovoltaic farms would cover 30,000 square miles of otherwise barren land in the Southwest. They would resemble Tucson Electric Power Companys 4.6-megawatt plant in Springerville, Ariz., which began in 2000 (left). In such farms, many photovoltaic cells are interconnect-ed on one module, and modules are wired together to form an array (right). The direct current from each array "ows to a trans-former that sends it along high-voltage lines to the power grid. In a thin-"lm cell (inset), the energy of incoming photons knocks loose electrons in the cadmium telluride layer; they cross a junction, "ow to the top conductive layer and then "ow around to the back conduc-tive layer, creating current.

68 SCIENTIFIC AMERICAN January 2008

and it would be reasonable for the natural gas industry to invest in such a network.

Hot Salt Another technology that would supply perhaps one " fth of the solar energy in our vision is known as concentrated solar power. In this design, long, metallic mirrors focus sunlight onto a pipe " lled with "uid, heating the "uid like a huge magnifying glass might. The hot "u- Plentiful Resource SOURCE FOR MAP: COURTESY OF NATIONAL RENEWABLE ENERGY LABORATORY; DON FOLEY (illustrations) id runs through a heat exchanger, producing Solar radiation is abundant in the U.S.,

steam that turns a turbine. especially the Southwest. The 46,000 For energy storage, the pipes run into a large, square miles of solar arrays (white insulated tank "lled with molten salt, which re- circles) required by the grand plan Average Daily Total Radiation tains heat ef"ciently. Heat is extracted at night, could be distributed in various ways; (kWh/sq m/day) creating steam. The molten salt does slowly one option is shown here to scale.

cool, however, so the energy stored must be NOTE: ALASKA AND HAWAII NOT SHOWN TO SCALE 8 7 6 5 4 3 2 tapped within a day.

Nine concentrated solar power plants with a electricity could be generated 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a day. PAYOFFS total capacity of 354 megawatts (MW) have Existing plants prove that concentrated solar been generating electricity reliably for years in power is practical, but costs must decrease.

Foreign oil dependence cut from 60 to 0 percent the U.S. A new 64-MW plant in Nevada came Economies of scale and continued research online in March 2007. These plants, however, would help. In 2006 a report by the Solar Task Global tensions eased and do not have heat storage. The " rst commercial Force of the Western Governors Association military costs lowered installation to incorporate it a 50-MW plant concluded that concentrated solar power could with seven hours of molten salt storage is provide electricity at 10 cents per kWh or less by Massive trade de"cit being constructed in Spain, and others are be- 2015 if 4 GW of plants were constructed. Find- reduced signi"cantly ing designed around the world. For our plan, ing ways to boost the temperature of heat ex-16 hours of storage would be needed so that changer "uids would raise operating ef"ciency, Greenhouse gas emissions slashed Domestic jobs increased Photovoltaic array Electricity delivered to the grid Junction box Su n li gh t (p ho ton s)

Current Electron "ow creates current Transparent conductive layer Cadmium sul"de semiconductor Junction Cadmium telluride semiconductor Conductive metal Power conditioner and transformer Glass w w w. S c i A m . c o m SCIENTIFIC AMERICAN 69

too. Engineers are also investigating how to use PINCH POINTS Stage One: Present to 2020 molten salt itself as the heat-transfer "uid, re- We have given considerable thought to how the ducing heat losses as well as capital costs. Salt Subsidies totaling $420 solar grand plan can be deployed. We foresee is corrosive, however, so more resilient piping billion through 2050 two distinct stages. The "rst, from now until systems are needed. 2020, must make solar competitive at the mass-Political leadership needed Concentrated solar power and photovoltaics production level. This stage will require the to raise the subsidy, represent two different technology paths. Nei- government to guarantee 30-year loans, agree possibly with a carbon tax ther is fully developed, so our plan brings them to purchase power and provide price-support both to large-scale deployment by 2020, giving New high-voltage, subsidies. The annual aid package would rise them time to mature. Various combinations of direct-current electric steadily from 2011 to 2020. At that time, the solar technologies might also evolve to meet de- transmission system built solar technologies would compete on their own mand economically. As installations expand, pro"tably by private merits. The cumulative subsidy would total engineers and accountants can evaluate the pros carriers $420 billion (we will explain later how to pay and cons, and investors may decide to support this bill).

one technology more than another. About 84 GW of photovoltaics and concen-trated solar power plants would be built by Direct Current, Too 2020. In parallel, the DC transmission system The geography of solar power is obviously dif- would be laid. It would expand via existing ferent from the nations current supply scheme. rights-of-way along interstate highway corri-Today coal, oil, natural gas and nuclear power dors, minimizing land-acquisition and regula-plants dot the landscape, built relatively close tory hurdles. This backbone would reach major to where power is needed. Most of the coun- markets in Phoenix, Las Vegas, Los Angeles POWERSOUTH ENERGY COOPERATIVE trys solar generation would stand in the South- and San Diego to the west and San Antonio, west. The existing system of alternating-cur- Dallas, Houston, New Orleans, Birmingham, rent (AC) power lines is not robust enough to Ala., Tampa, Fla., and Atlanta to the east.

carry power from these centers to consumers Building 1.5 GW of photovoltaics and 1.5 everywhere and would lose too much energy GW of concentrated solar power annually in the over long hauls. A new high-voltage, direct- "rst "ve years would stimulate many manufac-current (HVDC) power transmission back- turers to scale up. In the next "ve years, annual bone would have to be built.

Studies by Oak Ridge National Laboratory indicate that long-distance HVDC lines lose far less energy than AC lines do over equivalent spans. The backbone would radiate from the Southwest toward the nations borders. The lines would terminate at converter stations where the power would be switched to AC and sent along existing regional transmission lines that supply customers.

The AC system is also simply out of capacity, leading to noted shortages in California and other regions; DC lines are cheaper to build and require less land area than equivalent AC lines. About 500 miles of HVDC lines operate in the U.S. today and have proved reliable and ef"cient. No major technical advances seem to be needed, but more experience would help re-

"ne operations. The Southwest Power Pool of Texas is designing an integrated system of DC and AC transmission to enable development of 10 GW of wind power in western Texas. And TransCanada, Inc., is proposing 2,200 miles of HVDC lines to carry wind energy from Mon-tana and Wyoming south to Las Vegas and beyond.

70 SCIENTIFIC AMERICAN January 2008

construction would rise to 5 GW apiece, help- domestic jobs notably in manufacturing solar [THE AUTHORS]

ing " rms optimize production lines. As a result, components would be created, which is sever- Ken Zweibel, James Mason and solar electricity would fall toward six cents per al times the number of U.S. jobs that would be Vasilis Fthenakis met a decade ago while working on life-cycle kWh. This implementation schedule is realistic; lost in the then dwindling fossil-fuel industries.

studies of photovoltaics. Zweibel more than 5 GW of nuclear power plants were The huge reduction in imported oil would is president of PrimeStar Solar in built in the U.S. each year from 1972 to 1987. lower trade balance payments by $300 billion a Golden, Colo., and for 15 years was What is more, solar systems can be manufac- year, assuming a crude oil price of $60 a barrel manager of the National Renew-tured and installed at much faster rates than (average prices were higher in 2007). Once solar able Energy Laboratorys Thin-Film PV Partnership. Mason is director conventional power plants because of their power plants are installed, they must be main-of the Solar Energy Campaign and straightforward design and relative lack of en- tained and repaired, but the price of sunlight is the Hydrogen Research Institute in vironmental and safety complications. forever free, duplicating those fuel savings year Farmingdale, N.Y. Fthenakis is after year. Moreover, the solar investment would head of the Photovoltaic Environ-Stage Two: 2020 to 2050 enhance national energy security, reduce "nan- mental Research Center at Brook-haven National Laboratory and is It is paramount that major market incentives cial burdens on the military, and greatly de-a professor in and director of remain in effect through 2020, to set the stage crease the societal costs of pollution and global Columbia Universitys Center for for self-sustained growth thereafter. In extend- warming, from human health problems to the Life Cycle Analysis.

ing our model to 2050, we have been conserva- ruining of coastlines and farmlands.

tive. We do not include any technological or Ironically, the solar grand plan would lower cost improvements beyond 2020. We also energy consumption. Even with 1 percent annu-assume that energy demand will grow nation- al growth in demand, the 100 quadrillion Btu ally by 1 percent a year. In this scenario, by consumed in 2006 would fall to 93 quadrillion 2050 solar power plants will supply 69 percent Btu by 2050. This unusual offset arises because of U.S. electricity and 35 percent of total U.S. a good deal of energy is consumed to extract and Brilliant?

energy. This quantity includes enough to supply process fossil fuels, and more is wasted in burn- Far-fetched?

all the electricity consumed by 344 million plug- ing them and controlling their emissions. For a discussion with in hybrid vehicles, which would displace their To meet the 2050 projection, 46,000 square the authors about the solar grand plan, please visit our Community gasoline counterparts, key to reducing depen- miles of land would be needed for photovoltaic page at http://science-DON FOLEY dence on foreign oil and to mitigating green- and concentrated solar power installations. That community.SciAm.com; click on house gas emissions. Some three million new area is large, and yet it covers just 19 percent of Discussions, then Technology.

Underground Electricity Storage Electricity from to the grid photovoltaic farm Generator Natural gas-fueled Excess electricity produced during combustion chamber the day by photovoltaic farms Exhaust heat would be sent over power lines to Recuperator (pre-heats air) compressed-air energy storage sites close to cities. At night the Water-cooling tower sites would generate power for consumers. Such technology is al- Compressors Low-ready available; the PowerSouth pressure Motor turbine Energy Cooperatives plant in Mc- High-pressure Intosh, Ala. (left), has operated turbine since 1991 (the white pipe sends air underground). In these designs, incoming electricity runs motors and compressors that pressurize sed r e lea te air and send it into vacant caverns, Air ener y a g

mines or aquifers (right). When the to tricit l e c e

air is released, it is heated by burn- ped ing small amounts of natural gas; i r p u mve r n A ca e o g the hot, expanding gases turn i n t s to ra for turbines that generate electricity. ern C av w w w. S c i A m . c o m SCIENTIFIC AMERICAN 71

Although the suitable Southwest land. Most of that land is barren; there is no competing use value. And the ongoing research would improve solar ef"cien-cy, cost and storage.

$420 billion is land will not be polluted. We have assumed that Under these assumptions, U.S. energy de-substantial, only 10 percent of the solar capacity in 2050 will come from distributed photovoltaic installa-mand could be ful"lled with the following capac-ities: 2.9 terawatts (TW) of photovoltaic power it is less than tions those on rooftops or commercial lots going directly to the grid and another 7.5 TW the U.S. Farm throughout the country. But as prices drop, these applications could play a bigger role.

dedicated to compressed-air storage; 2.3 TW of concentrated solar power plants; and 1.3 TW Price Support of distributed photovoltaic installations. Supply program. 2050 and Beyond would be rounded out with 1 TW of wind farms, Although it is not possible to project with any 0.2 TW of geothermal power plants and 0.25 exactitude 50 or more years into the future, as TW of biomass-based production for fuels. The an exercise to demonstrate the full potential of model includes 0.5 TW of geothermal heat solar energy we constructed a scenario for 2100. pumps for direct building heating and cooling.

By that time, based on our plan, total energy The solar systems would require 165,000 square demand (including transportation) is projected miles of land, still less than the suitable available to be 140 quadrillion Btu, with seven times area in the Southwest.

todays electric generating capacity. In 2100 this renewable portfolio could gen-To be conservative, again, we estimated how erate 100 percent of all U.S. electricity and more much solar plant capacity would be needed un- than 90 percent of total U.S. energy. In the der the historical worst-case solar radiation spring and summer, the solar infrastructure conditions for the Southwest, which occurred would produce enough hydrogen to meet more during the winter of 1982-1983 and in 1992 than 90 percent of all transportation fuel de-and 1993 following the Mount Pinatubo erup- mand and would replace the small natural gas tion, according to National Solar Radiation supply used to aid compressed-air turbines.

Data Base records from 1961 to 2005. And Adding 48 billion gallons of biofuel would cov-COURTESY OF NREL again, we did not assume any further techno- er the rest of transportation energy. Energy-re-logical and cost improvements beyond 2020, lated carbon dioxide emissions would be re-even though it is nearly certain that in 80 years duced 92 percent below 2005 levels.

Concentrated Solar Large concentrated solar power plants would complement photo-voltaic farms in the Southwest. The Kramer Junction plant in Californias Mojave Desert (left), using technol-ogy from Solel in Beit Shemesh, Isra-el, has been operating since 1989.

Metallic parabolic mirrors focus sun-light on a pipe, heating "uid such as ethylene glycol inside (right). The mirrors rotate to track the sun. The hot pipes run alongside a second loop inside a heat exchanger that contains water, turning it to steam that drives a turbine. Future plants could also send the hot "uid through a holding tank, heating molten salt; that reservoir would retain heat that could be tapped at night for the heat exchanger.

72 SCIENTIFIC AMERICAN January 2008

Who Pays? MORE TO dies would end from 2041 to 2050. The HVDC Our model is not an austerity plan, because it EXPLORE transmission companies would not have to be includes a 1 percent annual increase in demand, The Terawatt Challenge for Thin subsidized, because they would " nance con-which would sustain lifestyles similar to those Film Photovoltaic. Ken Zweibel in struction of lines and converter stations just as today with expected ef"ciency improvements in Thin Film Solar Cells: Fabrication, they now " nance AC lines, earning revenues by energy generation and use. Perhaps the biggest Characterization and Applications. delivering electricity.

question is how to pay for a $420-billion over- Edited by Jef Poortmans and Although $420 billion is substantial, the an-Vladimir Arkhipov. John Wiley &

haul of the nations energy infrastructure. One Sons, 2006.

nual expense would be less than the current U.S.

of the most common ideas is a carbon tax. The Farm Price Support program. It is also less than International Energy Agency suggests that a car- Energy Autonomy: The Economic, the tax subsidies that have been levied to build bon tax of $40 to $90 per ton of coal will be Social and Technological Case for the countrys high-speed telecommunications required to induce electricity generators to adopt Renewable Energy. Hermann infrastructure over the past 35 years. And it Scheer. Earthscan Publications, 2007.

carbon capture and storage systems to reduce frees the U.S. from policy and budget issues carbon dioxide emissions. This tax is equivalent Center for Life Cycle Analysis, driven by international energy con"icts.

to raising the price of electricity by one to two Columbia University: Without subsidies, the solar grand plan is im-cents per kWh. But our plan is less expensive. The www.clca.columbia.edu possible. Other countries have reached similar

$420 billion could be generated with a carbon conclusions: Japan is already building a large, The National Solar Radiation tax of 0.5 cent per kWh. Given that electricity Data Base. National Renewable subsidized solar infrastructure, and Germany today generally sells for six to 10 cents per kWh, Energy Laboratory, 2007. has embarked on a nationwide program. Al-adding 0.5 cent per kWh seems reasonable. http://rredc.nrel.gov/solar/old_ though the investment is high, it is important to Congress could establish the " nancial incen- data/nsrdb remember that the energy source, sunlight, is free.

tives by adopting a national renewable energy There are no annual fuel or pollution-control The U.S. Department of Energy plan. Consider the U.S. Farm Price Support pro- Solar America Initiative:

costs like those for coal, oil or nuclear power, and gram, which has been justi"ed in terms of na- www1.eere.energy.gov/solar/ only a slight cost for natural gas in compressed-tional security. A solar price support program solar_america air systems, although hydrogen or biofuels could would secure the nations energy future, vital to displace that, too. When fuel savings are factored the countrys long-term health. Subsidies would in, the cost of solar would be a bargain in DON FOLEY be gradually deployed from 2011 to 2020. With Sunlight coming decades. But we cannot wait un-a standard 30-year payoff interval, the subsi- til then to begin scaling up.

Critics have raised other con-Pipe cerns, such as whether material "lled with constraints could sti"e large-scale ethylene glycol installation. With rapid deploy-ment, temporary shortages are Parabolic trough possible. But several types of cells exist that use different material com-binations. Better processing and recy-Heat exchanger cling are also reducing the amount of ma-terials that cells require. And in the long term, Electricity to old solar cells can largely be recycled into new the grid solar cells, changing our energy supply picture from depletable fuels to recyclable materials.

Superheated The greatest obstacle to implementing a re-Ethylene water "ow glycol " ow newable U.S. energy system is not technology or money, however. It is the lack of public Return awareness that solar power is a practical alter-water "ow Steam native and one that can fuel transportation as condensation well. Forward-looking thinkers should try to unit inspire U.S. citizens, and their political and sci-enti"c leaders, about solar powers incredible Future plan:

potential. Once Americans realize that poten-Steam turbine heat-holding tank tial, we believe the desire for energy self-suf"-

(molten salt) ciency and the need to reduce carbon dioxide Generator emissions will prompt them to adopt a nation-al solar plan. g w w w. S c i A m . c o m SCIENTIFIC AMERICAN 73