renewable energies in 2007

8/14/2019 Renewable Energies in 2007

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Renewable Energies in 2007A Critical Review ofFuture Energy Supplies

byErnst BucherProf. em. University of KonstanzAcademic Advisor and ConsultantTable of Contents:1. Foreword 12. Introduction 33. Solar thermal energy 84. Solar electricity 115. Biomass 236. Other forms of primary renewable energies: 26

Wind, hydroelectric power, geothermal power7. Energy conservation 298. Chiles potential of renewable energies 319. The freshwater problem 3410. Conclusions 3711. Figures 3812. References 97

1. ForewordThis paper represents a summary of several lectures presented at theUniversity ofSantiago de Chile in March 2007 and also on the level of two ChileanGovernmentCommissions (CORFO, NCE). A detailed analysis of Chiles energy situationwilltherefore be included in this study (chapter 8), resulting from recent energysupplycuts (oil, gas) by Argentina. It will be demonstrated that taking appropriateaction,Chile could become quickly and completely independent from imports offossil

fuels, including an expected annual growth rate in energy production of 500MWper year, without an increase of energy costs. The implications of thisunusuallyfavourable situation for Chile will be pointed out. A special chapter (chapter8) willbe dedicated to this point, which however is also relevant to several othernations.An abundant, cheap, clean and secure energy supply is a prerequisite for


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decent human living conditions and a healthy economy. The soaring gas andoilprice during the recent years is of considerable concern to society andeconomy.The prices have increased more than five fold since 1998; i.e. an average

annualincrease of 23 % over the past 8 years. There are three reasons to this: The oil companies did not discover new large oil fields during the lastdecades and therefore did not invest in new oil fields and refineries. Some of the big oil suppliers are politically unstable countries. South East Asia (China, India, South Korea e.g.) with more than 1/3 of theworld population is in a state of enormous economic growth with anincreasing energy demand.All these factors are responsible for the dramatic increase of energy costs,but onthe other hand also for the unusual demand and growth of alternative energy

development and production. The wealthy industrialized nations arebecomingincreasingly aware of this situation and also of the climatic consequences oftheirexcessive fossil fuel burning resulting in a faster than expected globalwarming andan increased catastrophic weather pattern.The IPCC (Intergovernmental Panel on Climate Change) reports of the U.N.released in Paris in March and April 2007 sent an alarming message to allnationsabout the negative side effects of accelerated CO2 production: droughts,

increasein number and intensity of hurricanes, floods, increase of sea level and loss ofhabitats for at least 200 million people.These facts are also realized by less wealthy nations, often becoming themostaffected victims of climatic disasters, though their energy consumption is 1-2ordersof magnitude lower than that of industrialized nations. In fact the wealthy of theworld population is responsible for 88 % of the world energy consumption,and

therefore for the consequences of it. A few nations are fully aware of thissituationand have developed a constructive legislation to promote alternativeenergies.Germany and Japan are the world leaders in promoting the development ofalternative energies. Germanys Einspeisegesetz1 (EEG) put into effect in1991for wind energy and later expanded to other alternative energies like solarthermal,


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geothermal, photovoltaic, biomass etc. demonstrated its success and hasnowbeen adopted by over 40 nations worldwide.1 engl: legislation about production and reimbursement of energy fed into the grid1

The purpose of this paper is 4-fold:

To present a general review of all renewable energies and to supplyinformation about yield (harvest factors) efficiencies and realistic costs. To explore the potential of all types of renewable energies worldwide aswellas for two special cases: Germany and Chile. To point out the economic, social and environmental benefits of renewableenergies: how nations will become quickly self sufficient and independent ofenergy imports (gas, oil, coal, uranium) thus avoiding conflicts about energyresources, and all this without an increase of energy costs. To point out the ramification of the energy crisis to other serious problemslike freshwater supply, hunger, pollution, illiteracy, etc. Because freshwater

production needs energy, it will also be briefly mentioned at the end of thispaper (chapter 9).This paper is intended to be readable and understandable for non experts ofscience and engineering (e.g. lawyers, economists, experts in social scienceandpolitics). Therefore it will not cover complex scientific and technical details.2

2. IntroductionThe world energy consumption in 2005 was evaluated to135000 billion kWhwith an increase of 2.7 % in 2005 (4.3 % in 2004) slightly higher than theaverage2.25 % during the preceding three decades. The spectrum of the worldenergyproduction 2004 is shown in Fig. 1. About 88.5 % of the energy is producedfromnon-renewable sources (oil, gas, coal, uranium) resulting in 39 billion tons ofwastedumped annually into the biosphere. The oil equivalent of our annual energyconsumption is a cube of size of 2.382 km (1 oil = 10 kWh). Fig. 2 shows thepopulation growth, energy consumption and CO2 concentration in our

atmospherebetween 1800 (beginning of industrialization) and now. The population isexpectedto reach 6.7 billion people in 2007 with a growth rate of 1.2 % per year. Theincrease of energy consumption and the corresponding increase of CO2productionhowever is mainly the result of industrialization. In 2007 we have a CO2 levelof


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390 ppm which means an increase of 39 % compared to a level of 280 ppmin thepre-industrial era. This is the highest level ever detected during the past700000years. It is interesting to compare the energy consumption and its CO2

productionper capita of several nations:Nation Populationin 2005(in millions)Energyconsumption(in 103 kWh/y)CO2production(in tons per capita)Percentage of

annual energyconsumptionUSA 297 112 20 25Germany 83 55 10 3.0Chile 16.0 18 3.8 0.21China (PR) 1310 10 3.7 10.0India 1084 5.0 0.8 4.8Africa (exceptSouth Africa) 849 4.8 0.6 3.0Bangladesh 145 1.6 0.21 0.17Average 21 3.8USA and Germany (as relevant of most industrialized European nations) areoftenreferred to as a 12 or 6 kW society respectively, i.e. every person isconsidered asan engine running 7 days a week all year round and permanently consumingapower of 12 or 6 kW respectively. The Chilean population can thus beconsideredto be a 2 kW society, a goal which is often postulated by environmentallyconcerned European scientists and politicians. The energy consumption percapitais evidently correlated with the wealth and lifestyle of a nation (see firststatementin chapter 1 and the table above).In Fig. 3 and Fig. 4, the spectrum of the energy consumption of Germany andChile is displayed. They both show the strong dominance of non-renewableenergies. However Chile does not have a nuclear part and Germany exhibitsa


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noticeable fraction of renewable energy of 4.2 % with a strong annualincrease.Germany has set an ambitious goal to increase this fraction to 25 % by 2020toreduce the nearly 100 % imports of gas and oil. In 2006 11.8 % were reached

surpassing the goal for 2006. In addition 130000 jobs were created. This itto be3

considered as a very wise decision in view of the fact that dependence onenergysupplying countries can lead to political blackmail and even war as we haveallwitnessed in recent years.It is expected that oil and gas wells will dry up in the foreseeable future.Assuming that we have burned all our fossil fuels on our planet, we are facedtothe question: What will be our energy sources?We will have 2 global sources: Solar energy with all its variants such as solar thermal and solar electricenergy, wind energy, energy from biomass, hydroelectric energy etc. Nuclear energy from current 235U fission reactors2, fast breeders using 238U,239Pu and 232Th and nuclear fusionSome singular local sources like geothermal energy, tidal power or oceancurrentscannot be considered as a global solution.In the public it is often recommended that we should turn our attention tohydrogen as a solution for the post fossil fuel era. This point will be discussedlater.It is often argued that we have enough fossil energy for the next 2-3 decadesandtherefore we should let future generations decide. This argument however isunacceptable for several reasons: The change from a fossil era to a new energy technology takes time. Wecannot change it over a time span of a few years. This change involves newinventions, starting with laboratory experiments of universities andindustries. The time period between a basic invention and a commercialproduct is at least 20-30 years as demonstrated by numerous examples inFig. 5. With energy shortages occurring even now, scientists and politicians

must do every effort to secure an abundant, cheap and clean energy supplyto avoid economic collapse and social unrest. Fossil fuels like oil, gas and coal are precious primary energies and shouldnot be wasted to generate low temperature heat for warm water andheating. In most northern countries, warm water and heating contributesabout 20-30 % of the countries energy consumption. We should conservefossil fuels immediately for the petrochemical industry. The recent IPCC report predicts a gloomy picture of our planets future:droughts, increased hurricane activity, floods, mudslides, changes of sea


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currents, melting of ice caps, shortage of freshwater, famines etc. Mostexperts predict that it is already too late to avoid all these problems. We areheading towards a strong global warming whereas we should expect anastronomical cooling off period. A significant reduction in the consumption offossil fuels can only alleviate but not prevent all the predicted disasters

which we are beginning to witness.What is the best solution then for the post fossil fuel era? We can excludegeothermal, tidal power etc. as a global solution though it is important incertaincountries located at hot spots of our planet, mostly countries with volcanicactivity2 Uranium ore mainly exhibits 3 isotopes with about 99.28 % 238U, 0.71 % 235U and 0.0005 %234U. Currentfission reactors use 235U and require an enrichment of235U up to a level of 4-5 %. Fastbreeders use 238Uwhich is converted to 239Pu by fast neutron bombardment and afterwards 239Pu is used forfission.4

(geothermal energy) or countries where large differences exist between lowandhigh tide (up to 13 m) suitable for tidal electric power. Studies have shownhoweverthat the use of all possible tidal power worldwide could contribute at best 0.3% ofthe current world power consumption and thus tidal power must be ruled outas aglobal solution just as geothermal power.At this point we must discuss honestly the possibility of nuclear energy andcompare its advantages and disadvantages with all forms of solar energy.Presently (in 2007) we have worldwide 434 nuclear plants operating. Thesearefission reactors using the isotope 235U which makes up 0.71 % of the uraniumreserves. Proven uranium ore reserves, which are considered worth to bemined,will last about 40-70 years for the presently existing reactors. Additionalreactorsare currently planned in the USA, the Russian federation, China, India, Japan,France and Finland. Taking about 180 estimated new reactors into accountthe

uranium ore reserves are thought to last about 50 years comparable to fossilfuellike oil and gas. The shortage of235U is also drastically reflected by the rapidincrease of the uranium (U3O8) price:Price in USD per lb of U3O82001 7early 2007 95expected by end of 2007 125expected in 2008 255


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It is clear that the present nuclear 235U fission technology can never beconsideredas a sustainable solution. Even if the uranium reserves would not be the mainobstacle, we would need a number of about 30000 new nuclear powerplants of

1 Gigawatt size at 100 % duty cycle and an expected energy consumption of270000 billion kWh per year (twice the quantity consumed in 2005) in about30years. Neither the money (> 1014 USD) nor the capacity to build 30000nuclearpower plants are available. Even with the present 434 nuclear power plants,theproblem of radioactive waste disposal remains unsolved in most countriesafter halfa century! We would pollute our planet with enormous amounts ofradioactive

waste for millions of years, a decision most people consider unethical andirresponsible towards future generations. We lack experience with long termbehaviour of such radioactive deposits.The above arguments are countered by the nuclear lobby:a) Search and mining of less concentrated uranium oresb) Development of fast breeder technologyc) Development of new breeding cyclesThe answers to these arguments are:to a) The present energy payback time for a nuclear power plant is about 6-7years. The invested energy to mine less concentrated uranium ores willrapidly move this payback time towards the lifetime of nuclear power

plants and thus will make nuclear power absurd.5to b) Two attempts to build a fast breeder costing multi billion USD each (inJapan and in France) have badly failed3. This technology is not maturedyet and highly vulnerable. Who would like to see tons of high risk materialsbe transported on our highways and railroads (e.g. the lethal dose forplutonium is about 6 g) under the present wave of terrorism? And theproblem of radioactive waste disposal (plutoniums decay half time isabout 23600 years) remains still unsolved.to c) Alternatively to the (238U, 239Pu) breeding cycle requiring high energy(fast) neutrons, a new breeding cycle has recently been proposed for

neutrons of any energy:Th + n Th Pa + e 233U + e92233912339023290

It is argued that this cycle generates less radioactive wastes and of shorterlifetimes. In addition, the thorium reserves are estimated to be 4 timeshigher than for uranium which would guarantee nuclear fuel for at least


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10000 to 20000 years. Thorium rich ores are found e.g. in India, Braziland Madagascar. Nevertheless, the risk of accidents and the pollution withradioactive waste still exists considering the large number of nuclearpower plants that would be required.Finally, the possibility for a successful fusion reactor is extremely small. The

experimental reactor to be built in Cadarache4 (France) costs about 20 billionUSDand will not feed energy into the grid. The fusion reactors may perhaps beconsidered commercial at best after 2048 but even then the construction ofsuch areactor requires several years. We need clean cheap energy now.In addition, the apparently low cost of nuclear energy is incorrect, leavingasidethe enormous risk factor (no insurance company will insure a nuclear powerplant),the costs for waste disposal and the enormous budgets for nuclear energy of

mostindustrialized countries are not taken into account. These factors lead to atotallydistorted market as compared with solar energy (see Fig. 32).In contrast to nuclear energy, solar energy is offering multiple solutions withriskfree, proven technologies, no waste problems and even a more favourableCO2balance (except biomass which is more or less neutral) than nuclear energy.It isfar less vulnerable to terrorism and prevents widespread blackouts due to

moredecentralized power production. The often reported higher costs for solarenergycan easily be refuted, if all the hidden costs of fossil fuels (environmental,health,corrosion) and nuclear energy would be taken into account. The truth is that,including all the hidden costs, the present price per kWh would have to betripled[2] and indeed would even considerably exceed the costs for wind and solarthermal heat and electricity.3 280 MW fast breeder Monju in Fukui, Japan built in 1994 was switched off in 1995 and

1200 MW fastbreeder Superphenix in Creys-Malville, France built in 1986 was switched off in 1996 bothdue to technicalproblems with the liquid sodium cooling system.4 ITER = International Thermonuclear Experimental Reactor is expected to generate 500 MW.The project issupported by the European Union, Japan, Russia, PR China, Southern Korea, India and USA.6

The facts presented here are also reflected in polls taken worldwide: e.g. inArgentina: Their weighted priorities given to various primary energy sourcesare


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hydrogen as an energy carrier as wind energy, photovoltaic and solar thermalenergy power stations (and also part of biomass systems) produce electricitycompatible with existing infrastructure (electrical network). Further researchwill notsolve these problems as the losses have fundamental physical reasons.

Thereforewe must conclude that hydrogen will not solve our impending energy crisis.7

3. Solar thermal energySolar energy has many aspects shown below:Harvest Tools Applications End usewarm waterheatingair conditioninglow temp heat heat(50-100C)

flat collectorsvac. tube collectorshot air collectorsthermoelectricgeneratorselectricityparabolicconcentrators(~85 suns)solar farmshigh temp. heat electricity

mirrors (heliostats,103-104 suns)solar tower electricitysolar fuels (H2)electricity solar cells grid remote el. powerelectricity fed intogridDC and ACelectricityIn this chapter the salient features of harvesting low temperature heat will bediscussed whereas chapter 4 will deal with the subject of solar electricity.

In Fig. 6 some basic numbers about solar irradiation are listed. Its abundance,compared to our energy need is most remarkable. The problem however isthe lowenergy density as compared to other power plants (hydroelectric, fossil fuel,nuclear). For practical purposes of applications, the average annualirradiation in aplace is a key figure. Chile is in a privileged situation with respect to solarirradiation with peak values up to 2300 kWh/m per year in the AtacamaDesert


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area with sunshine 83 % of the year, and the countrys average is 1540kWh/mper year exceeding Germanys average by 56 %. Even the changeableweatherpattern in the south of Chile is close to Germanys best area. As will be

pointed outlater, Chiles potential for renewable energies is one of the best in the world:solar,wind, biomass (wood, organic waste), hydroelectric and geothermalelectricitycould amply supply Chiles energy needs and thus make it totally self-sufficientincluding its increase of 500 MW per year (~1.6 %). Chile could even exporthighquality renewable energies and benefit by selling CO2 bonus values in themulti

million USD range.Solar thermal collectors were first mass-produced soon after the energy crisisinwinter 1973/74, following a jump of the oil barrel price from 2 to 60 USD. Itbecameobvious that at this price level, solar thermal energy would be cheaper thanburninggas or oil to produce low temperature heat. Although the oil price dropped to10USD per barrel in 1998, it newly reached a value of 80 USD in August 2006.The

installation of solar thermal collectors on buildings guarantees a stability ofheatsupply and also reduces the dependence on oil and gas, and thus also isexpectedto stabilize the oil and gas prices.8

Fig. 7 shows the basic diagram of a solar thermal collector system togeneratewarm water for households, industrial applications and heating of buildings.Innorthern areas where the temperature can drop below the freezing point, we

havetwo separate circuits:a) A heating circuit of the collector system with an antifreeze agent. Thewarm water is produced in a tank via a heat exchanger sitting on thebottom of the tank.b) A user circuit taking water from the top (because of the densitydifference between hot and cold water >4C)The two basic elements of a solar thermal unit are the collector and thewater tank


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which must be matched. In Central Europe we consider a storage volume of70-120 per m of collector area. The collector area must be chosenaccordingly tothe amount of heat used. We can design a collector according to itspurposes:

Warm water for household or industrial application Warm water AND heating (or air conditioning during the hot season)Some numbers for typical cases will be presented below.As we see in the bottom diagram of Fig. 7, we have a heat surplus in thesummerand a deficit in winter. Water is an excellent storage medium for lowtemperatureheat. With collector areas and tank volumes large enough, we can generatewarmwater from the sun for the whole year. However, since heating of buildingstakes

about 80 % of our heating budget, it is recommendable to use part of thecollectedheat for heating during winter time (see below).There exist two types of thermal collectors for buildings shown in Fig. 8(bottom): Flat plate collectors with an efficiency of 45-50 % Vacuum tube collectors with efficiencies in excess of 75 %, which are moreexpensiveThe performance of these two collector types is compared in Fig. 9.Efficienciesdepend strongly on season and irradiation spectra. The solar radiation has

twocomponents: Direct radiation (only present during sunshine) Diffuse radiation (always present)In Fig. 10, the diffuse and direct part is given for three places: Berlin, Lisbonandthe desert. For flat plate collectors the direct radiation is the only importantpart. Itconsists of a layer of a so called selective absorber, a material which absorbswellwithin the solar spectrum to achieve maximum collection efficiency.

Absorption ofsolar radiation will heat up the absorber until it begins to emit in the infrared,but itsemission is far below a black body emitter due to a very low emissivity.Typicalmaterials are TINOX, whose characteristics are shown in Fig. 8 (top) orcermetslike Cr-Cr2O3, Ni-NiS, AMA coating [thin layer sequences of (Al2O3/Mo)n or(Al2O3/Pt)n].


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In contrast, vacuum tube collectors are based on tubes coated with selectiveabsorbers, mounted in the focal line of parabolic troughs and operated underhighvacuum in order to avoid convection losses. Due to this construction, theycan alsoabsorb a part of the diffuse radiation. This can be seen in Fig 9 (top) wheretheefficiency is considerably higher than flat plate collectors during the coldseasonwith low sunshine and a ratio of direct to diffuse radiation smaller than oneasshown in Fig. 10. It is important at this point to emphasize, that solar cellsalsoconvert all the diffuse spectral part with photon energies exceeding thespecificband gap whereas for flat plate collectors it is practically useless. For moredetailssee reference [3].For homeowners or industrialists, the question arises about the amortisationtime of solar thermal collectors for warm water production5 and/or heatingThisamortisation time depends on the solar irradiation (insolation), oil price anditsannual increase (17.5 % average increase over the past 10 years and 8-10 %further increase are estimated for the coming decade) and also on theinvestmentcosts of a solar collector system including storage system and labour. Basedonthese data it is a simple matter to demonstrate that the amortisation time inCentralEurope for a solar thermal collector system is about eleven years withoutsubsidiesand only slightly higher (~12 years) for a solar heating system. Theamortisationtimes are considerably reduced in Southern Europe to about 5-8 years. Tobecomefully self sustainable, a tank volume of about 50000 would be needed. The

energy payback time of a solar thermal heating system is about 1-2 years. Ofcourse by super insulation of walls and windows, the heating energy could bedrastically reduced to about one third, but that would also need an additionalinvestment.Solar cooling or solar air conditioningIn countries with hot summers and cool/cold winters, a more appropriatesolutionwould be a solar air conditioner rather than a solar heating system. Airconditioners


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need a lot of electrical power generating frequent blackouts due tooverloading ofthe grid. Using solar thermal air conditioners is an ideal solution to cut backelectricity consumption. They do not need large storage tanks and work bestduring

the most intensive sunshine. There is definitively a lack of good models ofsolarthermal air conditioners on the market. By granting subsidies, the buildup ofthemarket for solar air conditioners could greatly be accelerated and CO2emissionreduced.5 A household typically requires about 3000-4000 kWh per year based on a dailyconsumption of160 of 60C water.10

4. Solar ElectricityThere exist three ways to generate electrical power from solar energy whichwill bediscussed in the following subchapters:Chapter 4.1: Solar thermal electric power stationsThe heat is used to drive a steam turbine which generates electricity. Therearethree types of such systems called: Solar farms, operating at temperatures < 400C Solar tower systems operating in the high temperature range of 1200-2000C Dish-Sterling systems with a heat engine in the focus of a parabolic mirror.Chapter 4.2: Photovoltaic systemsSolar cells, converting radiation directly into electrical powerChapter 4.3: Thermoelectric generatorsHeat from black absorbers is directly converted into electrical power bymeans ofthe Seebeck-effect which is particularly large for semiconductors.The advantages of solar power over all other forms of power are remarkable: The potential of solar energy is largest among all renewable energies (seeFig. 11) 3 % of the worlds desert area is sufficient to satisfy the worlds energyneedin 2007 The solar energy resources are more evenly distributed than all otherrenewable energy sources Solar energy can easily be integrated into conventional steam turbinesystems generating electricity and therefore into our electrical grid system.This is also true for photovoltaic power using DC to AC inverters. Together with thermal storage and hybrid operation with biomass (gaseous,liquid fuels, solids e.g. wood pellets) a continuous energy production is


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possible4.1 Solar thermal electric power stationsSolar heat was used more than 2000 years ago when in 212 B.C. Archimedessetthe Roman fleet of Claudius Marcellus in Syracuse (Sicily) on fire by

concentratingsolar light with mirrors on the wooden ships. In 1746 Lavoisier built the firstparabolic concentrator and about one century later Augustin Mouchot builtthe firstsolar heat system using glass lenses at the worlds fair in Paris in 1861. FelixTrombe became another French pioneer building solar furnaces in thePyrenees in1951 and 1970 reflecting solar light by Heliostats into a parabolic mirror. Thesolarfurnace built in 1970 reached temperatures exceeding 4000C withconcentration

ratios of up to 20000.11Due to the finite distance and the diameter of the sun, the maximumconcentrationc2,max is given in a biaxial system as:4 46'4002,max 2 = =D

c(Biaxial system)where D is the divergence of the solar light defined by:

= 2 = 0.532 = 31.92'SES

D D Rwith the solar radius RS = 696350 km and the distance between sun andearth DSE(average 150 million km). For monoaxial tracking the maximumconcentration liessignificantly lower2 2151,max 2,max

= = =Dc cTechnically, concentration c 10 can be achieved in a simple way, for higherconcentration (10 < c < 100) we need parabolic trough like mirrors or Fresnellenses. Concentrations above 100 can be achieved by biaxial tracking ofmirrors(=heliostats) and reflection onto a solar tower, a parabolic mirror or into thefocal


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point of a parabolic mirror. Fig. 12 presents a schematic view of thesepossibilities.Fig. 13 shows a picture of the 1970s solar furnace of Odeillo along with somecharacteristic data.4.1.1 Solar thermal electric power stations: Solar farms

The first commercial production of solar thermal electric power stationsbegan in1984 when the first of nine SEGS (Solar Electricity Generating System, LUZEngineering Corp.) plants went into operation in the Mojave Desert(California,USA). By 1990 the 9th plant featuring an output of 80 MW brought the totallyinstalled power to 354 MW. Operating details of SEGS 9 are given below andFig. 14 presents a partial view of a SEGS plant (around noon time). The 8 mlongparabolic mirrors are provided with a silicon sensor as a sun tracking elementto

guarantee an optimum collection efficiency. Chlorinated high temperature oilispumped through the blackened tube surrounded by a Pyrex glass tube underhighvacuum to avoid convection losses. The typical feature of the 3rd generationSEGSplants (typically for SEGS 9) can be summarized as follows:These types of power plants are called solar farms or DCS systems(DistributedCollector System)Typical net capacity: 50-80 MW

Specific capacity per km 50 MW per kmSpecific annual energy harvest (per kW) 3200 kWh per kWSpecific annual energy harvest (per km) 1.6108 kWh per kmEfficiency (el. Output to solar energy input ratio) 14-15 %Operating temperature 350-390C (limit: 500C)Absorber type SS tube, oxide buffer, Mo,Al2O3 antireflection coating,Pyrex vacuum tubeSolar field aperture of used area 29 %Costs per kW investment 2800-3300 USD per kWCosts per kWh 0.105 USD per kWh12

The efficiency of 14-15 % is slightly lower than the best photovoltaic panels.It canbe broken off into three basic parts:Efficiency of concentrator 64 %Efficiency of receiver 72 %Efficiency of steam turbine 35 %Miscellaneous 89 %Total efficiency 14.3 %


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Efforts are being made to avoid the chlorinated oil and the heat exchangerand touse the DISS system (Direct Solar Steam System), developed at the ZSW inStuttgart/Ulm (Germany), which represents a challenging engineeringproblem of a

two fluid convection system, leading possibly to higher efficiencies and lowercosts.During the past 17 years, no new solar farms have been built due to longtermproblems emerging at the 9 SEGS plants. The recent shortage of oil and gassupply however led to a new, 4th generation solar farm type now underconstructionin various places: Spain, Italy, North Africa, South Africa, Near & Middle East,India, Mexico, USA, Australia etc. with a total of 2250 MW (already underconstruction or in the planning phase). The first 4th generation type is underconstruction west of Granada, on the Plateau of Guadix: Four units with a

totalelectrical power output of ~200 MW and a 7.5 tons full load molten saltstoragesystem, an annual net electrical production of 4 180106 kWh per year andaninvestment cost of 4 250 million . These systems are now commerciallyavailablein units of 50 MW. It is expected that with increased production the cost perkWhwill drop from 0.12 to 0.04 in 2020. An annual electricity production of 36billion

kWh is expected by the mid century, corresponding to an installed power of11.3 GW. The current construction capacity is about 4 units per year (=200MW peryear). However this would still be only 0.03 % of the present annual globalenergyconsumption. On a national scale however it would be a considerably higherpercentage of clean cheap energy.One of the basic fundamental problems of solar power stations is theirintermittent power production. In order to generate power 24 hours a day,theymust be built as hybrid systems with a conventional source like gas, oil, wood

orpossibly biomass. The hybrid fuel consumption could be considerablyreduced byadding a heat storage system (e.g. molten salt) with a high storage capacity.Thisin turn would need additional capacity to fill the storage system daily whichcouldserve as bridging system until the conventional system has reached fullcapacity.


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The general layout diagram of a new 4th generation solar farm is shown inFig. 15.13

4.1.2 Solar thermal electric power stations: Solar towersA second type of solar thermal electric power station has been developed:solartowers. Fig. 16 shows a picture of a solar tower (also known as CRS, CentralReceiver System) system, built in Daggett (California, USA) capable of a 10MWelectrical energy production. Similar tower systems have been built on thePlataforma Solar de Almeria (PSA, South-Eastern Spain). Solar tower systemshave achieved efficiencies of 14-15 % (comparable to solar farms) and thesesystems are also operated with heat storage systems (e.g. a hot rock tank) tobridge interruptions of sunshine up to a few hours. Solar towers are still in astateof pilot plants and not yet commercially available. From our presentexperience,they are more difficult to operate, in particular the start and shut downphases.Some models used liquid metal (e.g. sodium), others use hot air from a blackwiresystem. The potential for much higher efficiencies is much bigger for solartowersystems than for solar farms, but leads also to a higher complexity due tomaterialproblems. We will therefore not present more details of solar tower systemsas theyare still in a state of development.4.1.3 Solar thermal electric power stations: Dish-Sterling systemsA 3rd version of solar thermal electric systems has been developed over thelast 25years: Dish-Sterling systems. Fig. 17 presents a series of Dish-Sterlingsystems inthe test field PSA. Their advantage is a higher efficiency, a better flexibilityfor size,stand-alone operation and smaller applications of the order 10-50 kW ofelectricalpower production. They consist of a parabolic reflector with a heat engine in

itsfocal point and, to make use of the full potential, sun tracking is necessary.Thesesystems are still in a test and demo status. For periods without sunshine,backupoperation by heat storage and fossil fuels is under investigation.As the IPCC report is focussing its attention mainly on the CO2 emission,Fig. 18 presents a view of various CO2 emission rates of power stations.Several


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countries like China, USA or Australia raise objections against CO2 reducingtechnologies for economic reasons. Therefore Fig. 19 summarizes variouscostfactors of fossil fuels and some future technologies like liquid coal, shaleoil,

compared with solar thermal electric power generation. Fig. 19 might beused as arough guideline for all those involved in the decision making process. Fourimportant remarks however must be added: The fossil fuel energy costs in Fig. 19 are current estimates. These numberscould also be considerably higher in case of future energy shortages due towars or political unrest in oil producing nations The cost picture in Fig. 19 presents a distorted view about costs. The truecosts are those including all the environmental damage (e.g. acid rain, dyingof forests, pollution of lakes and rivers (loss of fish habitat) droughts,destruction by storms, floods, mudslides and their death tolls, health costs,

corrosion etc.) from fossil fuels. The true costs of fossil fuel energy areestimated to be three times higher [2] than the present cost thus makingsolar energy more attractive and even competitive. The risk of energy shortage in the fossil fuel area is considerable. Supplysecurity should be taken into account, too, upgrading the value of anindependent, renewable energy supply. Shortage of fossil fuel supply couldresult in considerable losses of industrial and agricultural production.14

It is well known that renewable energies are generators of new jobs.Producing energy in the own country instead of importing it, will improve thetrade balance and generate new jobs, reducing the jobless rate andtherefore lower social costs, besides making life more meaningful andhuman through income by a job.All these arguments are strongly in favor of accelerating the support andproduction of renewable energies and tipping the balance towards renewableenergies even now.4.2 Photovoltaic systems: Solar cellsIn contrast to solar thermal power stations, solar cells can convert solarradiationdirectly into electrical power at room temperature. To understand the detailsof thisprocess requires basic knowledge of solid state, semiconductor and device

physics. It cannot be discussed here. For those interested, I refer to theexcellentbooks of M.A. Green [4]. Instead, some general results will be given for nonexperts in this field.The first solar cell based on silicon was investigated in 1954 by Chapin, FullerandPearson at the Bell Laboratories in Murray Hill. It had a conversion efficiencyof5.6 %. Many other semiconductors were subsequently investigated and their


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performance optimized.The structure of a solar cell is shown in Fig. 20. Into a p-type doped wafer(typically boron is used as p-type dopant for silicon) a thin n-type doped layer(typically doped with phosphorus and about 500 thick) is created at thesurface

which is later on exposed to the sun. At the p/n transition the internalelectrical fieldseparates electron-hole pairs generated by absorbed photons. Anantireflectioncoating is located on top of a solar cell to reduce the reflection and thusimproveperformance. A metal grid penetrating this antireflection coating contacts thesiliconand reduces the internal resistance.One of the most important semiconductor parameter is the so called bandgap

Eg. It is the energy required to excite a bound electron in an atom of the solidandto make it itinerant. For silicon this energy is 1.12 eV at room temperature.Forgallium arsenide (GaAs) it is 1.43 eV. The optimum performance of a solarcelldepends strongly on this value Eg. Fig. 21 shows this dependence also knownasShockley-Loferski-Queisser curve.From Fig. 21 we can see that the optimum band gap Eg is around 1.5 eV. Theband gap of silicon is with 1.12 eV below this optimal value, however due to

its welldeveloped technology, its abundance and low cost, more than 98 % of allsolarcells are made from silicon. A few other important properties can be derivedfromFig. 21: The efficiency drops with increasing temperature. For silicon this effect isconsiderable: 0.48 % (relative) per C. E.g. the efficiency of a silicon solarcell drops from 16 % at 20C to about 12.9 % at 60C, a temperature whichis easily reached under full illumination and hot outdoor temperatures (e.g.in the desert)

The temperature dependence decreases with increasing band gap Eg Concentration increases the efficiency of solar cells, provided thetemperature is kept constant which necessitates cooling of the solar cell.15

A photovoltaic panel could achieve a much higher efficiency if solar thermalcollection would be taken into account. E.g. 16 % electrical efficiency and50 % thermal efficiency would result in an overall efficiency of 66 %.Research and development of such hybrid collectors have recently beenstarted worldwide.


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Next we will review the amount of electrical energy that can be harvested byasolar cell or a panel. This is summarized in Fig. 22. We compare GermanywithChile, a country with one of the largest solar irradiation in particular in the

desertarea in the north. These numbers will be important when comparing itspotentialwith other renewable energies and their costs. It is a simple matter tocalculate thatat current solar panel costs, the amortisation time of a photovoltaic system isof theorder 25 years without subsidies. Photovoltaic energy generation is still themostexpensive one among the alternative energies. Therefore photovoltaicenergy

needs a legislation to make it pay off faster. Germany has developed a socalledfeed-in law (not only for photovoltaic energy but also for other renewableenergies),which has been taken over by more than forty other nations to promote afasterdevelopment of renewable energies. It can easily be calculated from Fig. 22and anannual harvest of 360 kWh/m that a desert area of 390000 km (i.e. asquare withside length of 624 km) would completely satisfy our planets annual need for

energy(about 140000 billion kWh). This calculation is engendering the questionaboutresources. Among all photovoltaic materials only silicon can satisfy thedemands ofsuch immense resources. In Fig. 23 a status report of all currently knowncommercial solar cells is presented.As can be seen from Fig. 23, 98.2 % of all solar cells produced in 2005 aremade from silicon: 93.5 % are based on crystalline (wafer) silicon technologyand4.7 % use amorphous silicon technology (thin film cells). CdTe and

Cu(In1-xGax)Se2-ySy cannot compete with silicon simply for reasons of theirlimitedresources. Silicon is the only high efficiency solar cell technology withunlimitedresources that could supply a noticeable fraction of our energy need. There ishowever a market for light weight thin film cells with a value of 200-300 Wper kgcompared to 10-20 W per kg for wafer based silicon cells6. Only 3 cell typesexist


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with efficiencies higher than 20 %: silicon, GaAs and InP (indium phosphide).Sofar multicrystalline cells of GaAs and InP have not achieved good enoughefficiencies for mass production, because of their unfavourable grainboundary

problems. Higher efficiencies can be achieved with tandem cells withoptimizedband gaps and geometry. Maximum efficiencies for tandem cells are showninFig. 24. For reasons of their technical complexity, only double tandem cellshavebeen developed (except amorphous silicon). Concentration can also lead tohigherefficiency. In both cases, cooling is necessary. Fig. 25 summarizes the resultswithtandem cells achieved so far. The highest efficiency of a dual cell is 34 % for

onesun and 37 % for 500 suns. Concentrator cells need a special design of themetalgrid. The first panels with Fresnel concentration lenses and small cells havebeenbuilt by ISE, Freiburg as shown in Fig. 26.6 Most crystalline silicon solar cells are based on 200-300 m thick silicon discs called wafersas shown inFig. 20. These cells may generate about 100 W per kg, but due to their fragility, the cellsmust be protected bya glass cover and aluminum back resulting in a lower specific power generation of 10-20 Wper kg. In

contrast, thin film technology is based on a 10-20m silicon layer deposited on a (possiblybendable)substrate. Layers of this thickness are less fragile and therefore thin film cell panels do notneed heavy weightprotection components. This technique allows a better specific power generation of about200-300 W per kg.16

It is a widespread error that many people believe producing solar cellsinvolvesmore energy than ever harvested during its lifetime. Some energy paybacktimes ofsolar cells are given below:

Material Energy payback timein years( = 16 %, 1 kWh/Wp per year)CO2 savings per kW and yearin tons( = 16 %, 1 kWh/Wp per year)mono Si 51 0.5multi Si 3.51 0.6amorphous Si 1.50.5 0.63Cu(In1-xGax)Se2-ySy 1.40.5 0.63


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CdTe 1.00.3 0.64Windmill (70 % dutycycle of full power, 1 MW) 0.40.1 4.1Suppliers give warrantees of 25-30 years for photovoltaic systems. Thereforethe

saving factor is given by the ratio lifetime to energy payback time which is atleast6-9 for crystalline silicon and 20-30 for thin film cells. Here again, we noticethesuperior, favourable data for wind energy compared to photovoltaic energygeneration in addition to its much lower costs.In relation to Fig. 22, we compare the harvest factors of other renewableenergies in Fig. 27. For solar towers, farms and photovoltaic systems they areallcomparable. Strikingly large values can be found for wind generators,hydroelectric

power plants and of course oil, gas and coal as primary energy sources. Astrikingfact are the low harvesting factors of biomass. It has to do with the lowefficiency ofthe photosynthesis process. We have to come back to this point in chapter 5.One of the basic problems with photovoltaic power is its high cost, thehighestamong all alternative energies. Solar cell production involves many hightechnology steps. The costs can be broken up into several parts as shown inFig. 28. The basic problem is to invent cheaper process technologies and atthe

same time improve efficiencies. Mass production is expected to reduce costsas iswell known from Moores empirical law. The costs have indeed decreasedduringthe last 25 years since the production for terrestrial applications started (seeFig. 29). The costs for thin film cells are about half, however their efficienciesarelower and therefore the net energy costs are only about 30 % lower (see Fig.27).It is predicted however that mass production of Cu(In1-xGax)Se2-ySy moduleswill

lead to a sharp reduction of costs. in contrast to Fig. 29, the module prices ofsilicon have increased due to an unexpected silicon shortage on the marketin turndue to a decade long growth of the solar cell market between 35 % and up to62 %in 2003 leading to an expected totally installed photovoltaic power of about9.5 GWby the end of 2007. The world capacity of solar cell production in 2007 isabout


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2.75 GWp. With nearly 50 % of its capacity, Germany is the leader in cell andmodule production. Some details of raw silicon and cell production are giveninFig. 30. As we can notice from this table, many new silicon producingcompanies

will emerge in 2008 and 2009 to satisfy the needs of the solar cell market. Itisexpected that this will lead again to a continuous reduction of the panel costsandcost per kWh as shown in Fig. 29.17

It is interesting to compare the various investment costs for renewableelectricenergies:Solar thermal systems(towers and farms)Photovoltaicsystems Biomass Wind2800 USD 6500 USD 2200 USD 1400 USD per kW2300 USD (offshore)Although photovoltaic power is considered the most expensive one amongrenewable energies, it is interesting to demonstrate that the price per kWh iscompetitive over long periods of time. The reason for incorrectly calculatedhighenergy costs is the unrealistic short pay-off period set by investors orbankers,mostly 5 years, whereas these power plants operate for many decades. As anexample we choose a recently (3/29/07) completed photovoltaic power plantinSerpa (south eastern Portugal). We will analyze its cost and performance andcompare the results with a wind park.The symbols have the following meaning:I0 Investment costs (e.g. a bank loan for a power station)z Number of years for linear pay-off (I0/z per year over z years)p interest rate (currently about 6 % by world bank)A0 Annual maintenance and service costs averaged over z yearsH Harvest in kWh/Wp per yearP0 Peak power in W

percentage of full power operation annuallyThe average cost c per kWh is given by:

[P zI p z z Ac + + + =


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00 0

8.76( 1)]21

(in USD per kWh)during the period of z years of pay-off time.We now apply this formula to the recently (3/29/07) completed photovoltaicpowerplant in Serpa mentioned earlier:I0 61 million 80 million USDz 20-40 yearsp 6 % as currenly used by world bankA0 1 % of I0 per year(photovoltaic systems exhibit low maintenance cost)

H 3.0 kWh/Wp per year(sunshine 3300 hours per year, monoaxial tracking)P0 11 MW 25.3 % (6.09 hours per day)18

The resulting costs are as follows for variable pay-off time and interest rateCosts(in USD per kWh)Pay-off time(in years)Interest rate(in %)

Lifetime of system(in years)0.22 20 6 200.12 20 0 200.18 30 6 300.16 40 6 400.14 20 6 300.12 20 6 40It is interesting to compare the energy costs of the most expensiverenewableenergy above with the cheapest one under the same conditions: wind energy

provided that wind conditions are sufficient:For a wind mill of 5 MW size we have the following values:I0 2.4 million USD on land, 3.25 million USD offshorez 10-20 yearsp 6 % as currently used by world bankA0 5 % of I0 per yearH 3.5 kWh/Wp per yearP0 5 MW 40 %


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Costs(in USD per kWh)Pay-off time(in years)Interest rate(in %)

Placement0.018 20 6 land0.024 20 6 offshore0.025 10 6 land0.033 10 6 offshoreFrom this example, we can draw several important conclusions: Wherever we have good wind conditions, wind power is the best economicchoice as long as it does not interfere with a quality of life of people and theenvironment in general. The wind electricity costs are considerably lowerthan any other energy source. Due to its short energy payback time it is thebest weapon against the increasing CO2 level.

In general wind parks have higher maintenance costs than photovoltaicpower plants One of the drawbacks of wind energy is the intermittent unpredictableenergy production, whereas for photovoltaic power plants in desert areas itis much more predictable. For energy production around the clock, we needa combination of different renewable energies or hybrid systems: wind,photovoltaic, stored energy, together with biomass (biogas, bio fuels andsolids like wood or wood pellets). Alternatively if biomass is not available, itcould be hydroelectric power or fossil fuels. Its consumption could beconsiderably reduced up to 50 % or more-19

Though photovoltaic power is the most expensive one among therenewableenergies, it is nevertheless competitive over long periods of time. The safetyand predictable energy production, the more decentralized power production(reduced risk of terrorism) and the independence of fossil fuel shortagemake it attractive. In addition the present excessive use of fossil fuelsgenerates high additional costs [2] (health, environmental damage,corrosion in particular) and they are expected to increase considerably. Economists and politicians must be convinced that short term solutions(over periods of election terms) will no longer work and that breakinginvestment barriers for renewable energies will pay off in long term.

The true energy costs have been evaluated for the whole spectrum ofprimaryenergy sources and are presented in Fig. 31 [12]. The value for photovoltaicpower(MaxNet Costs) is however considerably overestimated.In 2nd or 3rd world countries it is often considered too expensive to build solarcell factories. However their beneficial factors must not be overlooked: Theygenerate new high quality jobs and secure electricity production. For remote


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applications in dry hot countries, photovoltaic power is particularly suitableas willbe shown later in this chapter. The costs of long power lines can be avoided.In 3rdworld countries, in areas more distant than about 4 km, it is cheaper to install

photovoltaic systems than a connection to the grid (in Europe this distance isanorder of magnitude shorter). In Fig. 32 the costs to build a 60 MW silicon solarcellfactory are given. Compared to the enormous costs to plan and build anuclearpower plant, an investment of about 60-70 million USD with annualproductioncosts of about 150-200 USD is comparably low compared to an equivalentnuclearpower plant, with all the risks and its complexity involved. A note is also in

order toall those groups considering to set up research groups of new materials forphotovoltaic systems. Referring to Fig. 5, a time span of 20-25 years has tobeconsidered between the discovery of a new material and mass production. Inorderto contribute a significant portion to our energy consumption, it is suggestedthatonly elements with sufficient abundance on this planet should be consideredforfurther basic research: Na, Mg, Al, K, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Ga, B, C, N, O,

P,S, Se. Fig. 33 shows the general five stages of solar panel production. Theonlymass produced cell types are crystalline silicon, amorphous silicon, CdTe andCu(InGa)(SeS)2, the latter three being all thin film cell types.Applications of photovoltaic powerApplications of photovoltaic power in the range of 1 W-1 MW are numerous inindustrial countries and in remote areas for: Educational programs via remote TV courses Telecommunication (private + central, phone, FAX, computers) Water desalination and pumping stations

Irrigation and reforestation for food and biomass production Water sanitation (by UV radiation and ozone) Lighting (private and public)20

Households (cooking, washmachines etc.) Refrigeration (food storage) Solar air conditioners Medical care Power supplies for agricultural tools


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Charging units for batteries Waste disposal Solar electric vehicles (bikes, cars, wheelchairs, boats, buses, trains,planes) Solar cloths for powering low power applications (bikes, wheel chairs)

Solar fuels produced by biomass combined with photovoltaic energy(Methanol CH3OH, Ethanol C2H5OH, hydrogen H2, methane CH4, carbonmonoxide CO) Photovoltaic and solar thermal hybrid panels generating heat andelectricity Some examples for less known applications are given in Fig. 34-38:Fig. 34: The first transparent cell producing electricity. Transmittance 5-25 %suitable for public buildings like train stations, airports, winter gardensor storage rooms manufactured by the company sunways (Konstanz,Germany) only.

Fig. 35: 100 kWp photovoltaic panel serving as noise protection in the valleyof theRhine built in 1989 by TCN consulting. The system exhibits an energyharvest of about 110000 kWh per year.Fig. 36: Pictures from solar bike race 1999 across Australia. The bikes,developedby the Swiss engineer Prof. Andrea Vezzini at the Technical University ofBiel (Switzerland), achieved a maximum speed of 90 km/h and an averagespeed of 66 km/h.Fig. 37: Solar dress, possibility to power bikes by solar clothes. The switchfrom

800 million cars to bikes would cut back fuel consumption, reduce pollutionand noise, ease traffic and avoid further highway construction. Applicationof photovoltaic power to mass produced goods for daily use like bikes areparticularly effective and useful.Fig. 38: (top) First photovoltaic powered train built in Italy. (bottom) Picture ofasolar airplane designed by the engineers Andr Borschberg and BertrandPiccard powered by the sun only and expected to fly around the world in2009.The advantages of photovoltaic power are numerous: Virtually no maintenance (mainly DC to AC converters for grid connection)

Long lifetime (more than 30 years), large harvest factors Zero energy costs (no fuel has to be bought)21

Quiet (no movable parts) No pollution, CO2 level reduction Independence of energy market and shortages Safe and secure Cheap for long term applications Off-grid applications


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4.3 Thermoelectricity: Direct heat to electricity conversionFor reasons of completeness, the direct conversion of heat to electricityshouldalso be mentioned. It can be achieved through the high thermopower of semiconductors and certain metals (e.g. Heavy Fermion type metals). Applications

areconsidered in the 1 W to 1 kW range. Their conversion efficiencies are lowerthanfor photovoltaic conversion within the temperature range of applications. Wewillnot discuss this aspect further as it will not play a significant role tocontribute tothe worlds energy problem. For those interested I refer to the excellent bookofI. Goldsmid [6].4.4 Solar fuels

Together with bio fuels, solar fuels are also now and then considered as asubstitute for fossil fuels. By solar fuels we mean the direct conversion ofsolarenergy to fuels, e.g. hydrogen, or the synthesis of methanol (CH3OH) orethanol(C2H5OH) from CO2 and water via solar energy. This is not yet a commerciallyavailable process but it would be desirable for its CO2 neutrality. In particular,thehigh concentration of CO2 from fossil fuel burning power stations (oil, gas,coal,biomass) could be recycled instead of being released into the atmosphere.

Thisprocess is still in a state of laboratory experiments and considered tooexpensiveas it needs high temperature (> 250C) and high pressure (> 50 bars) toenforceone of the endothermic chemical reaction:H CO CH OHH CO CH OH H O2 32 2 3 2

23+ + +Using carbon monoxide (CO) as raw material provides virtually water freemethanoland therefore requires no further refinery in contrast to the reaction based oncarbon dioxide (CO2). Both reactions require hydrogen (H2) and thus aproductionfacility with access to (solar) hydrogen would be favourable (see below).


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Another solar thermal cycle system has recently been tested at the Paul-ScherrerInstitute (Villigen, Switzerland) with a pilot production plant being built inIsrael. It isa high temperature cycle requiring the structure of a solar tower plant with

temperatures of 1200C. The thermochemical cycle involves only non-toxicelements and can yield either metallic Zink for electricity production of aZn/Airbattery or solar hydrogen (H2) from a Zn/H2O reaction. However, as desirableashydrogen might be as energy carrier for environmental reasons, it suffersfromserious disadvantages as outlined at the end of chapter 2. In case wheresolarhydrogen can be used directly for chemical reactions, such applications maysome

day become reality. The details of this process are outlined in Fig. 39.225. BiomassBiomass as a base for energy production can mean many different things: Organic waste from farming, gardening and households, sewage, liquidmanure, animal waste from slaughterhouses etc. Crops as corn, sugar beets, sugar cane, wheat, rapeseed, miscanthus,arundo donax, millet, cotton, soybean, castor, switch grass, grass Trees as kienaf, eucalyptus, oil palms, coconut, palms, birch tree, asp tree,ash tree, poplar, willow, elm tree, fir tree etc.The products of biomass can be biogas, wood or wood pellets, methanol,

ethanol,bio diesel, heat and electricity. In dealing with biomass we have to answerthreefundamental questions:1. Energy harvest in kWh per area (km) and year2. Net energy gainenergy inputNEG = energy output3. Cost per kWh of every form of bio energy (e.g. biogas, bio fuel)The general use of biomass and its conversion to other conventional forms ofenergy is given in Fig. 40. Organic waste containing predominantly a lot of

watercan only be converted effectively to biogas by a liquid fermentation processasdescribed under methods. Burning of organic waste with a concentration ofwaterhigher than 85 % is endothermic and should be avoided. Biogas obtainedfromliquid fermentation is a dirty fuel and must be refined for use as acommercial fuel.


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It contains too many toxic impurities (see bottom of Fig. 40). The conversionfromsolid fuels (wood, residues from biogas and bio fuel production) to liquid fuelsisstill a challenging problem needing more research and development. Unlike

coalliquefaction it is not yet a fully commercialized process.The question of whether we could produce enough energy just from thephotosynthesis process on this planet is answered in principle in Fig. 41. Thecalculation of this global calculation could also serve for individual countries(seealso Fig. 46, biomass potential in Germany). It is possible to produce enoughbiomass just from 13.5 % of our forest area. This is of course a theoreticalresult asnot all our forest area is easily accessible to harvesting biomass. Some of itcould

also be grown in desert like areas. In this case however, we would need a lotoffresh water and that also costs energy. As shown on the bottom, theefficiency ofbiomass growth and energy harvest is low due to the low efficiency of thephotosynthesis process, which is about an order of magnitude lower than asolarcell or a wind mill. Among biomass we have many different forms. Theabsoluteenergy value of different biomass species is listed in Fig. 42, in order tocompare

them and convert them correctly.23Bio ethanolA major advantage of biomass is its compatibility with the present energyinfrastructure. The composition of refined biogas is close to natural gas andthuscan be used as a substitute. Bio fuels as ethanol or bio diesel can be usedandstored in the same way as conventional gasoline and petroleum diesel. Theycanbe mixed with conventional fuels and cars can be easily tuned to biogas or

biofuels. In Fig. 43 some characteristics for plants, shrubs and trees useful fortheproduction of bio ethanol are summarized. Bio ethanol is produced fromstarch orsugar containing plants whereas bio diesel is produced from oil containingplants,shrubs and trees (see Fig. 44). There is a considerable controversy aboutsome


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plants to produce bio ethanol. Some experts have figured out a negative energy balance for severalspecies. In particular for corn and in particular if grown in dry areas. Toproduce 1 of bio ethanol (= 5.9 kWh) from corn, a minimum of 4.6 m ofwater is needed [7]. This groundwater can be regarded as about 20-25 % of

its energy. To these irrigation costs further energy costs for growthimproving products (like fertilizers, pesticides and herbicides), harvesting,fermentation and refining have to be added. In particular the use ofchemicals is expensive (energy wise). Using desalinated freshwater insteadof groundwater would need nearly three times more energy than gainedfrom 1 of bio ethanol. Therefore biomass can never be produced efficientlyin areas where desalinated water is needed. The production of bio fuel from plants that need a lot of water willacceleratethe growing freshwater crisis further (see chapter 9) and make it even worsethan the energy crisis.

The use of corn to produce ethanol has increased its price from 128 USDper ton to 335 USD per ton (i.e. a factor of 2.7!). Thus car drivers aresubsidized on cost of the poorest people of the world for whom corn is abasic daily food.Similar conclusions about a negative balance for bio ethanol made from cornhavebeen reached by Pimentel (see Fig. 44, bottom). The negative conclusionshavebeen countered by five independent study groups. However their conclusionsof anenergy gain of 34 % is meagre and possibly doubtful. In practice this means

thatcorn as a source of bio fuel generates more problems than it is expected tosolve.Among the plants used for producing bio ethanol, sugar cane is the onlyundisputed one. It has the highest energy harvest factor of 8.3 (ratio ofenergyoutput to input) close to the maximum of 10.2. The CO2 saving benefit is 85-90 %.The annual production is around 18 billion supplying a noticeable fraction ofabout50 % of Brazils need for fuelling its car fleet. Worldwide however bio fuel

production is only about 3.4 % of the worlds need for fuel for its 800 millioncarsrunning on our streets.24

BiodieselIn Fig. 44, the most common plants and trees used for the production of biodieselare listed. For bio diesel, similar to bio ethanol, the cultivation of thosespecies


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used for bio diesel is problematic: The destruction of tropical rainforests for the cultivation of oil palms,coconutpalms or soybeans is even counterproductive for the CO2 balance,destroying the habitat of the tropical fauna, flora and even primitive people.

It only helps non fossil fuel countries to secure fuel supply on cost of theenvironment. Though the use of bio diesel appears to have a beneficial effect on thelifetime of diesel engines, it was recently reported that exhaust products ofbio diesel generates a far higher health risk to people than petroleum diesel.E.g. the cancer risk is up to a factor of 30 higher than for petroleum diesel. The excessive production of bio diesel will lead to higher prices for productsmade from oil and will dramatically worsen the freshwater shortage. It willalso reduce the production of food, like cereals.In Fig. 45, the chemistry of bio diesel and the exponential growth of the useof bio

diesel in Germany mostly produced from rapeseed are described. The use ofbiodiesel in 2005 was 180000 tons (+71.4 % compared to 2004). The capacityin2006 for bio diesel production in Germany is 3.4 million tons. One of the basicreasons was the passed legislation of tax exemption for bio fuels. From thecultivated farming area in Germany of 110000 km in 2006, 12.4 % wereused forbiomass production (in 1996 it was a negligible 0.3 %). In Fig. 46, Germanysbiomass potential is evaluated to 21 % of its total energy consumption in2005.

In conclusion, we should consider bio waste as an energy source and use iteffectively instead of dumping it. Absolute priority must be given to foodproductionto keep its price at current levels. Biomass production should only be allowedinnon used agricultural areas or semi arid areas. Tropical forest areas must beprotected against greedy bio fuel companies. The production of bio fuelsmust becarefully analyzed for their energy balance and possible environmental andsocialdamage.25

6. Wind and hydroelectric power6.1 Wind powerWind power is (besides hydroelectric power) the biggest contributor toelectricityproduction among the renewable energies. Fig. 47 shows the exponentialgrowth,starting from zero in the early 90s to 130 GW expected in 2010. In Germanywhere


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the booming wind industry started to take off following the legislation infavour ofthe feed-in law (the so called EEG - Energie Einspeise Gesetz) in 1991,electricityproduction from wind energy has surpassed hydroelectric energy production

in2006. For Germany we have for 2006 the following statistical data (fromDEW,Deutsches Windenergie Institut).Totally installed power 20.62 GWNumber of wind generators 18685Annual energy production 30.5 billion kWh(=5.7 % of electricity consumption)(=0.74 % of total energy used)Annual CO2 saving 26.1 million tonsNumber of created jobs 73800

(of 130000 in renewable energies)Guaranteed price per kWh 5.5 ct (on land)6.19 ct (offshore) 2 % degressionStarting with wind energy, the EEG made Germany the worlds leader with11.8 %of renewable energy production in 2006.As shown previously (chapter 4), wind power is the cheapest amongrenewableenergies, with costs of 2-5 cts per kWh, short energy payback time and largeharvest factors of 2.5-4 kWh/Wp per year with a theoretical maximum of8.76 kWh/Wp per year. Under certain excellent wind conditions, up to 6

kWh/Wpper year can be expected (e.g. Tierra del Fuego, Patagonia) which wouldevenreduce the above costs by nearly a factor of two, if used where the energy isproduced.Though the intermittent energy production presents a problem, it can bereduced if wind mills are distributed over a wide area. With current DC highvoltagetransmitting power lines in the million volt range, losses over distances to1000-2000 km can be substantially reduced and make even remote wind parks

economic. The most ideal solution of wind parks is a hybrid power station incombination with biomass (biogas, bio fuels or solid biomass) or fossil fuels intheworst case.Wind mills are currently on the market between 1 kW to about 6 MW, just topower electrical applications in homes or mobile homes up to larger cities. Asaguideline a 1 MW wind mill can supply electrical power to 600 households(4 persons each) or 100 % power to 150 households (Western Europes 6 kW


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society).The specific energy harvest per km and year of wind mills and wind parks isgiven in Fig. 27. The reason for lower values of wind parks compared to windmillsis the rule of thumb to keep a distance between wind mills about five times

thediameter of the rotor blades. For a 5 MW wind mill, the rotor blades have adiameter of 126 m. Shorter distances could reduce the power output ofindividual26

wind mills of a wind park, under average wind conditions. In areas ofexcellent windconditions, encountered e.g. on the south tip of South America or Scotland,thesenumbers could be up to 60 MW/km or more and an annual energy harvest ofup to500 million kWh/km, i.e. an order of magnitude larger than photovoltaicpowerstations. In areas with excellent wind conditions, power is also produced atnight,which is impossible for photovoltaic systems. Wherever possible, wind energyisthe first choice. Fig. 48 shows the characteristic output versus wind speed. Ingeneral full power is achieved at wind speeds of 40-50 km/h levelling off athigherspeed. At low speeds (v), the power output varies as v. The currently usedwindpower is only a small fraction of 0.5 % of the immediately feasible possibilityof 53million GWh per year corresponding to nearly 40 % of the worlds energyconsumption and a theoretical maximum of about 120 % of it (see Fig. 49).Together with all other renewable energies, 240 % of the current energyneedcould be generated.Over the past three decades three generations of wind mills have beendeveloped as shown in Fig. 50. The conventional wind mills using gears havereached a maximum power of 5-6 MW (3rd generation) with increasing costs.A

new gearless type has been developed (4th

generation) with higher efficiency,lower cost, lower maintenance and longer lifetime. Two generators aremounted onthe top of the wind towers, which is built by extrusion technique of concreteorconcrete & epoxy. This technology offers a lot of savings as no high risecranes willbe needed. Fig. 51 and Fig. 52 display specific performance data forstarwind


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type wind mills, confirming the low costs of wind electric power.6.2 Updraft wind powerIn desert areas, a new and different type of thermal wind generators forelectricityproduction has been invented and is under construction in Manzanares

(SouthSpain): Updraft wind towers. A large area around a tall tower, about 1000 mhigh iscovered with slightly tilted concentric collectors. Underneath the collectors,the airis heated and streaming up the wind tower. The area under the collector canstillbe used for agricultural purposes. Some characteristics are given in Fig. 53,alongwith the picture. The expected costs of its generated electrical power areestimated

between 13-15 cts/kWh, considerably higher than conventional electricalwindpower. The first prototype has been designed by W. Schleich and partners inStuttgart (Germany). Another disadvantage is shared with photovoltaic powerstations, that it does not generate power at night, in contrast to conventionalwindmills.6.3 New hydroelectric power sources Besides conventional hydroelectric plants, which we will not discuss here,new ideas of hydroelectric power generation are discussed. The worlds firsttidal electrical power plant was built on the northeast coast of France at the

mouth of the Rance river. In contrast to conventional hydroelectric powerstations, a tidal power plant generates power only during the flow of low andhigh tides, i.e. 50 % of the time. This is reflected in a much lower annualenergy harvest of about 2.5 kWh/Wp comparable to the harvest of a goodphotovoltaic power station. The prerequisite of large differences betweenlow and high tide is met in many other places. The total contribution isevaluated to 170 GW and an annual energy harvest of 360 billion kWh, i.e. acontribution of 0.27 % to the present worlds energy consumption.27

In certain areas of the sea we have strong ocean currents (e.g. SanFrancisco Bay area, Strait of Gibraltar). They could serve to generate a

considerable amount of electricity by submarine turbines (see Fig. 55). Theirpower generating capacity could be increased by combining them with windgenerators mounted on the pedestals. Recently, it was argued [9] that hydroelectric power could be expanded byexploiting also smaller rivers without the construction of dams. Turbinescould be suspended from bridges or from rafts tied to the banks of the rivers.Power stations between 10 kW to 1 MW size could double the presentlygenerated hydroelectric power worldwide.


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Vast thermal energy resources are stored in the ocean. Pilot plants of 50kWsize have been built in the warm South Pacific Ocean exploiting thetemperature difference of 25C on the surface and 4C in deep water. Thistemperature difference leads to a maximum Carnot efficiency of 7.0 %, too

low for large scale energy production. Furthermore the energy must betransported from the open sea to the land.6.4 Geothermal energyGeothermal energy has two components: Surface heat stored from the sun Deep geothermal energy flowing from the hot centre of the earth to itssurface with a steady heat current of 0.063 W/m, leading to an increase oftemperature of about 3C every 100 m. In hot spot (volcanic) areas this canbe much larger. Geothermal heat is used in general by electrically drivenheat pumps from a depth between 2 and 100 m to heat buildings. Involcanic areas geothermal heat generates high pressure steam driving

turbines to produce electricity. Iceland e.g. is covering 75 % of its energyneed by geothermal electric power. Recently some projects have beenstarted to produce energy from deep drilling (5000 m) and injecting waterinto several hundred C hot, deep rocky area. Unexpectedly this processprovoked several earthquakes of magnitude 4-4.5 on the Richter-scale.These events led to a discontinuation of this project in Basel (Switzerland).Hot spots are often located in areas of geological instabilities. Therefore it isadvisable to pursue such projects in lesser populated areas than Basel.28

7. Energy conservationThe possibility to alleviate our energy crisis by energy conservation is

frequentlyneglected. Its advantages are: It is the cheapest energy source It saves money It conserves non renewable energy sources like oil and reduces its marketvalue and price It enhances the percentage of renewable energies It improves the environment It improves the quality of lifeEnergy can be conserved in many ways: Recycling: Paper, bottles, cans,

(Fig. 56) clothes, used goods Households: Use high efficiency appliances(Fig. 57) Lower thermostats in winter and raise it in summerUse organic wastes as energy sourceProper food selectionReduce throw away mentality (example: 1 computer isequivalent to 80000 kWh (same as a car) and replacing itevery year is a big waste of energy!) Traffic: Use public transportation (if possible)


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(Fig. 57 + 58) Car poolingAvoid short distance flightsUse bikes for short distancesUse energy conserving cars Industry: Use solar collectors on large buildings for heating or air

conditioningCar pools for employeesDevelop energy saving industrial processes and equipmentIn Fig. 56, the benefits of recycling are listed quantitatively. The spectralenergyconsumption in a household is analyzed in detail to suggest possibilities ofenergyconservation. Households are responsible for 28 % of Germanys energybudget.The reduction of energy consumption by a factor of 2, which is possiblewithout

reducing quality of life, would reduce Germanys energy consumption by 574billionkWh annually, i.e. by more than the presently generated renewable energy(about500 billion kWh annually). Saving 50 % of household energy would increasetherelative percentage of renewable energies from 11.8 % to 13.7 %.Fig. 57 lists the possibilities of energy (and money!) savings in households. Inparticular heating presents a big potential which amounts to about 30 % ourenergybudget. A remark about our eating habits is also in order. Red meat takes ten

timesthe energy to produce the same number calories. Importing red meat viaairplane29

increases this ratio another 1-2 orders of magnitude. We list below a fewproductsto give consumers an idea:Product Energy ratio (importedversus domestic products)Producing country andtransportation

Meat, Apples 400-600South Africa, Argentina,New Zealand, Chile:(air cargo)Tomatoes 11 Spain (via truck)Strawberries 25 Israel (air cargo)More than 1/3 of the western population is suffering seriously from obesity(=overeating, mostly energy intensive food), generating additional healthcosts and


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e.g. leads to buy a fitness bike (which in turn also costs a lot of money andenergy)to reduce weight. .Consuming local seasonal food, stop overeating andavoidingimported products from far away countries would improve health, save

money andhelp our local farmers for a better income. These few facts should be addedtoFig. 57 to demonstrate the irrationalities of our energy wasting, globalization-crazysociety and how each individual shares responsibility to the serious globalwarming, pollution and all its adverse effects.Traffic is another very sensitive area, where a lot of energy could be saved. Itaccounts for about another 1/3 of our total energy budget. 18.5 % account forourcar fleet (Germany). 73 % of the 760 billion annually driven kilometres are

drivenby the driver alone. 25 % of these 760 billion kilometres are rides shorterthan 1 kmfor which a brisk walk or bike ride would not only be more economic but alsomorebeneficial to health. Fig. 58 presents a diagram of the costs of our mobility-crazysociety. It shows how energy efficient a bike is and how energy wasting shortdistance flights (of 200-1000 km) and cars are. The discussion about thecontribution of these energy inefficient means of transportation and itscontribution

to our environmental problems is widely a taboo, but must be brought to theattention of responsible politicians by scientists.Fortunately, some new hope is visible on the horizon, arising from progress innew electricity storage by light weight batteries suitable for electric cars (seeFig. 59). For a range of 50-100 km the change from combustion engines toelectrical vehicles (cars, motos and solar bikes) would cut fuel consumption,pollution and noise considerably and improve our quality of life. The basicmodelfor future suburban traffic would be to park electric vehicles of workers at theworking place and to recharge them during the working hours by solarelectricity or

wind energy. The development of light weight batteries (super caps) withweightabout 3-4 kg/kWh (compared to 30 kg/kWh for a lead acid battery) wouldhave atremendous synergetic effect on the use of solar electricity (mainlyphotovoltaicenergy). Therefore research and development should be strongly encouragedalsoin the area of electrical energy storage.


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30

8. The potential of renewable energies in ChileChile is one of the more favourable countries for the development ofrenewableenergies. The only major part is currently hydroelectric power which amounts

toabout 14 % for the total energy consumption and 52 % for the electricityproduction(see Fig. 4). In Fig. 60, some realistic but conservative estimates arepresented forthe development of all possible renewable energy sources. It can easily beconcluded that Chile has a most realistic possibility to be energy self-sufficient andcover all its energy needs by a combination of all its existing renewablesources,without increasing the energy costs.

8.1 Solar electricitySolar electricity in the northern desert area, where large amounts ofelectricity areused by the mining industry, losses and cost of transportation would beminimal.The main problem is to generate power continuously. This can be achievedbyhybrid systems together with huge thermal energy storage tanks (moltensalt)bridging power production for up to 6-7 hours and biomass from southernareas or

wind energy from the near coastal area.8.2 Wind energyThe southern tip of Chile (Tierra del Fuego) exhibits one of the mostfavourablewind conditions of the world with harvest values 2-3 times higher thanelsewhere. Ithas a low population density (0.8-1.2 capita per km) and there would berarelyopposition to build large wind parks. There are many unpopulated islands,whichwould be more economic than offshore parks (costing about twice as much

as onland wind parks). The wind parks could be distributed over large areasreducingthe fluctuations of power generation. The southern part is particularly suitedforrenewable energies as the problem of intermittent and fluctuating energyproduction of solar- and wind power could be smoothed out by abundantbiomass


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(e.g. fast growing pines and fir trees). Furthermore the southern areas havemanyunpopulated valleys that could produce additional hydroelectric power andevengeothermal power in hot spot areas. The excess power from the south would

haveto be transported to the north via high voltage DC power lines over distancesaslong as 2000 km in order to alleviate the power problem in the metropolitanSantiago area or some of the larger cities in the area. Assuming an oil priceof70 USD per barrel (=159 =1590 kWh) means a price of electricity from oil ofatleast 10 cts/kWh whereas a 4th generation wind mill would produce electricityfor 2cts/kWh, i.e. 5 times cheaper and avoiding dependence on the fluctuating

fossilfuel market, which is expected to go up beyond 100 USD per barrel over thenextyear, besides the independence and security of energy supply.8.3 BiomassOrganic waste from farms, households and wineries could produce about 8 %ofthe countrys energy need. Organic waste should be considered as valuableenergy source for biogas or bio fuels instead of being dumped into pits wheretoxicand climate detrimental methane is released into the atmosphere by open

fermentation. The southern part benefits from the existence of fast growingpines31

and firs and some other trees that could be considered as a valuable sourceforbiomass: wood pellets or bio fuels made from wood which could serve ashybridsystems for solar and wind power plants. Wood could contribute as much as20 %of Chiles energy need. From Chiles 136000 km forest area (18 % of totalarea)

only about 30 % of the photosynthetic biomass production is currently used,mostlyin the south.8.4 Geothermal energyChile has also a considerable geothermal power potential and due to activevolcanoes and hot spot areas near the surface, 8-10 % of the energy needcouldbe covered by relatively easy to build surface power stations down to a few


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hundred meters. There exist many experienced companies e.g. in Iceland ortheUSA. However, in an area where earthquakes are to be expected, there is noexperience how to build earthquake-proof large power stations exceeding the50-

100 MW size.8.5 Hydroelectric powerThe potential for hydroelectric power is not fully exploited. There exist manyvalleysin the south, where dams could be built, or smaller hydroelectric plants asmentioned previously in smaller rivers could be exploited without damage tothecountryside. The fraction of 52 % of electricity production could easily beincreasedto 70-80 %, oil and gas imports be curbed and energy supply secured.However

the planning and construction of hydroelectric power plants takes manyyears,whereas several 100 MW solar energy power plants could be built over aperiod ofa year allowing for a fast improvement of the energy situation.8.6 RecyclingRecycling can save energy as outlined in chapter 7. Recycling in Chile couldbeconsiderably intensified and lead to substantial energy savings. In particular,energy contributes to about 50 % of the costs of aluminum cans. In Germanyrecycling adds 4 % of the energy savings. In Chile with only 1/3 of the energy

consumption per capita, the savings from recycling would be much higher,probably around 10 %.8.7 Conclusions Chile has a very large unexploited potential of a variety of renewableenergies: solar thermal, solar electricity, wind, biomass, geothermal,hydroelectricity and energy saving from recycling. Chile could not only be self-sufficient, but could even export cleanrenewable energy. The evaluation given in Fig. 60 is to be considered veryconservative and amounts to 150 % of the present annual energyconsumption. In Fig. 60, only large power plants bigger than 1 MW wereconsidered. Taking power generation by individual homes, public buildingsand industrial companies into account, at least another 10 % would bepossible. Self-sufficiency is peace politics and helps to avoid conflicts.32

The use of renewable energies (sun power, wind and biomass) couldalleviate Chiles energy shortage on a very short term basis, within 1-2 years, whereas hydroelectric or geothermal power would take 5-10 years. Chile does not need nuclear power. It would not help solving Chiles energyproblem before 2020, far too late. It would generate serious risks and aradioactive waste problem, in addition to a foreseeable uranium shortage


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By installing large scale CO2 neutral, renewable energy plants, Chile couldgenerate millions of income by selling CO2 certificates. It could reinvest thismoney in generating a sustainable regenerative energy industry, whichcould create between 10000 to 100000 jobs (about 5-8 jobs per MW ofrenewable energy like wind, biomass and solar power).

The security and stability of energy supply by using renewable energiescould be considerably increased and the disadvantage from high oil and gasprice strongly reduced. Brazil with its 50 % bio ethanol production is aconvincing example. Cutting back fossil fuel imports would strongly improve the foreign tradebalance, the environment and quality of life. Though the gradual change to renewable energies and self-sufficiency iscoupled to large investment costs, they will pay off soon. The costs mustalso be seen on the scale of the overall state budget. Creating new jobs willreduce the expenses for social aid and generate new tax income, besidesmaking life more human by reducing the unemployment percentage.

There is no doubt that the future for a healthy economy liespredominantly in large investments in renewable energies.33

9. The freshwater problemThe freshwater problem is best characterized by the following facts: 1.7 billion people (about 25 % of world population) suffer from inadequatedrinking water supply 2.7 billion people (about 40 % of world population) do not have sanitaryequipment 8 million people die every year from contaminated water, 35 million dieevery year from hunger

The situation is getting worse year after year By 2025, 3.5 billion people (about 50 % of the world population) will nothave adequate water supply All these people live in the tropical or subtropical areaA solution is available: Solar or wind power seawater desalinationThe worsening situation has a number of reasons: Depleted ground water reserves Dumping of toxic wastes, mostly by industrial nations and contaminatinggroundwater resources Climate change with global warming, less rainfall and drought periods Overuse of water resources by industrial companies

Irrigation for agricultural purposes Population growth Biomass production will sharply increase freshwater consumption. 1 of biofuel needs approximately 1000-5000 times more waterThe following table lists some (extreme) examples for freshwaterconsumption percapita and day:Dubai (UAE): 1000 per day (overall Dubai: 700000 m per day)Switzerland 480 per day (total)


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270 per day (households only)Africa 3-5 per day (desert areas)In Dubai and the Gulf States in general, freshwater is produced bydesalinationusing cheap oil. This is impossible in poor nations. The only way is using th

renewable energies in 2007

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