Global warming is real and the burning of fossil fuels is causing it. It is time to stop debating whether warming is in fact occurring and how soon its dire consequence will materialize and start to take action. The carbon dioxide content of the atmosphere can be reduced by removing it once it has already entered the atmosphere (planting trees), removing it from the flue gases before they are emitted into the atmosphere[1] or by not by not generating carbon dioxide at all, by replacing the fossil fuels with clean and un-exhaustible energy sources[2].
The time for just holding conferences and just writing articles is over. It is time to build those demonstration plants that will determine the feasibility and costs of the various alternative energy systems. It is time to get serious about the transition to the post-oil, clean and un-exhaustible solar-hydrogen economy.
The goal of demonstrating this technology by building pilot plants is to obtain reliable data, so that the debate over the feasibility of converting to the solar-hydrogen economy can be closed and the transition can start. The other goal of building demonstration plants is to identify and eliminate the technical bottlenecks, optimize the processes and to generate globally standardized specifications that would allow the mass production of the equipment.
Described below are solar-hydrogen generator units, which by 2050 could meet about 50% and by 2100 nearly 100% of mankind's energy needs. These packaged units should eventually be mass produced to generate both fuel and electricity. The smallest of thestandardizedhydrogen generator units, the 1,000 kg/yr capacity one would be designed to serve individual households, the 10,000 kg/yr unit for schools, hospitals and other institutions, the 100,000 kg/yr package to serve small communities, while the 1,000,000 kg/yr plant would become the power plant of the future.
Once these demonstration plants been built, a concentrated effort should be made to minimize their first and operating costs, maximize their efficiencies and to take advantage of free market competition to optimize their manufacturing, distribution and installation practices. If the best scientific talent is mobilized, it is estimated that by 2020 the cost of solar electricity can be reduced to between 5˘ and 10˘/kWh and the cost of the hydrogen equivalent of a gallon of gasoline to about $2.
This document describes the present state of the alternative energy technology, the features and operation of the equipment blocks comprising the solar-hydrogen demonstration plants and provides a roadmap for completing these demonstration plants by 2010.
During the last 50 years, the global population doubled, energy consumption
quadrupled[3] and the
global GDP increased 6 fold. This caused both global warming[4] and a possibility of energy wars,
which can turn nuclear. According to the 2007 report of the Intergovernmental
Panel on Climate Change, the mass extinction of species can occur[5]. It is estimated that in the next
50 years the global demand for electricity will triple. For these reasons and
because solar energy is practically unlimited, the petroleum based
economy[6] of the
20th century should be gradually replaced by a solar-hydrogen economy in the 21st
century. This conversion from fossil to clean and un-exhaustible solar energy
will require the mobilization of such scientific talent as did the Manhattan
Project and must be followed by an international effort on the scale of the
Marshall Plan.
When discussing global energy consumption, the unit most often used is the quad[7] (Q= 1015 BTUs[8]). Today, the global energy consumption is between 400 and 450 Q and is rising at a yearly rate of 20 Q. It is expected to reach 600 Q by 2020.. The distribution of the presently used energy sources are: oil (35-37%), coal (25-26%), natural gas (20-25%), wood/biomass (10%), nuclear[9] (7.5%) and renewable sources[10] such as hydroelectric power (2.4%), solar (0.6%), geothermal (0.4%) and wind[11] (0.05%).
As was shown in the figure above, the total fossil fuel reserves of the globe are estimated to amount to 75,000 Q and the global consumption from 1950 to 2000 increased from 100 to 400 Q. The figure above also shows that the total energy consumption (red line) is rising at a higher rate[12] than the supply of fossil fuels (solid blue line). The difference between the curves is being provided from nuclear and renewable sources. The fossil envelope (dotted blue line) describes the likely future consumption of fossil energy (coal, oil, natural gas). The area under this curve is the total of the known fossil reserves on the planet. The curve projects a maximum yearly fossil production capability of about 700 Q, which could occur around 2050 and the exhaustion of this energy supply by the year 2200.
Naturally, the curve does not reflect the consequences of global warming or of energy wars. In fact, besides the exhaustible nature of fossil fuels, their continued use also results in some 27 billion tons of carbon dioxide being released into the atmosphere[13].
Sir Nicholas Stern[14] estimated that by 2020 the effects of the resulting global warming will cause a 20% reduction in the global GDP. The continued reliance on fossil fuels is not only likely to result in "energy wars" but could also cause the collapse of the global economy. Yet none of these need to occur. There is still plenty of time to gradually convert to an inexhaustible and clean "solar-hydrogen" energy based economy, while reducing greenhouse gas emissions[15] some of the major companies are already making those changes[16].
Below, I will discuss a) the amounts of solar energy needed to meet the present and future global energy needs, b) the types and efficiencies of today's solar collector designs, c) the methods to convert solar generated electricity into chemical energy (hydrogen), d) the methods to compress, liquefy , store and distribute hydrogen, e) the investments and operating costs required for building a solar-hydrogen demonstration plant and f) the infrastructure needed to fully convert to this technology by 2050.
The amount of solar energy reaching a unit area (m2) is called "insolation". Insolation varies with the geographic area, with the weather, with the orientation of the collectors, and with diurnal and seasonal variations. High insolation areas on our planet are shown on the right side of the figure below. Naturally, in addition to the continents, solar energy can also be collected on floating islands in the oceans.
An example of an insolation curve is shown on the left side of this figure, corresponding to a clear March day in Draggett, California[17]. Assuming that this is an average day for the year and assuming that the collectors are provided with tracking mechanisms which continuously points them toward the sun, the total solar energy received per square meter of collector area is slightly under 4,000 kilowatt-hours/year (kWh/yr).
Today, the per capita energy use on the planet ranges from1,000 kWh/yr in Africa to 16,000 kWh/yr in Canada. Therefore, if the efficiency of a solar energy collection and conversion system is assumed to be 10%[18] and if the solar energy is collected in a high insolation region (such as Daggett, California), the per capita collector area required would range from 2.5 m2 for people livingin Africa to 40 m2 for the residents of Canada.
Using conservative insolation values (less than in Daggett, California) as the basis of the calculation, the collector area required to meet today's global energy needs is 3% to 5% of the area of the Sahara[19] (a large dot on the global map above). Naturally the total area of high insolation on earth is much larger[20] than that of the Sahara and solar energy can also be collected in areas of lower insolation[21] or in the oceans.
The thermal collectors on the roofs of private homes[22] usually serve to provide the residence with heat and/or hot water. The larger size thermal power plant designs on the market[23] are either concentrating[24] or flat, their operation is either stationary or tracking[25] and they can convert the
solar energy (photons) to thermal energy (heat), to electricity (electrons), or directly to hydrogen[26].
In this discussion, first the thermal designs will be described. These designs are often referred to as the solar-thermal-electric generating systems (SEGS). An example of that design is a 354 MW plant that has been in operation at Kramer Junction and Harper Valley in California since 1985. The main components and operation of that design is described in the figure above. In this design, parabolic mirror reflectors (troughs) are used to track the trajectory of the sun and to concentrate the sunlight onto absorber tubes that are located at the focal line of the parabolic mirrors. Inside the absorber tubes, heat resistant oil is circulated and serves to transport the collected heat into steam boilers, which provide the steam to drive the turbine generators[27].
In some of the more recent SEGS designs, the circulating fluid temperature has been more than doubled, while in others direct generation of steam (DSG) has been achieved, which increases the power production by some 15%.
The chimney effect generates an updraft because the heavier cold air on the outside displaces and pushes the lighter the warm air upwards in the chimney. This upward flow is caused by the pressure difference between the heavier cold air on the outside and the lighter warm air on the inside. Static home cooling systems utilize this effect to pull the cold air from underground ducts into the homes. In the winter, this same effect increases the heating load of high rise buildings, because the cold air is pulled in by the chimney effect at the bottom of the building and has to be heated. (I have eliminated this effect on the new IBM Headquarter Building at 590 Madison Ave in New York by equalizing the inside pressure with that on the outside.)
The solar updraft tower is a solar energy converter, which converts solar-based thermal energy into concentrated aerodynamic energy (wind). In this system air is heated under a circular greenhouse-like canopy. The roof of this canopy slopes upwards from the perimeter toward the center, where the tower stands. Under this canopy, the sun heats the air, which rises up the tower and generates electricity by driving an array of turbine generators.
This "low-tech" solar energy collector concept is over a hundred years old[28], but its first 50 kW working model was only built in 1982[29]. Today, much larger installations (50 to 200 MW) are planned in Australia[30], China[31] and the American Southwest. Thermal storage can be provided by covering the ground with heat absorbing surfaces, so that power generation can also continue at night. The investment cost (about $30/m2) and the solar energy collection efficiency (about 5%) are both low, while the energy payback period is expected to be 3-5 years.
PV collectors convert photons to electrons. Sunlight is composed of photons containing various amounts of energy corresponding to the range of wavelengths within the solar spectrum. In the photovoltaic (PV) collectors[32], when photons strike the cell, they may be reflected, pass through, or be absorbed, but only the absorbed photons generate electricity. This is because the construction material (the silicon atom in the crystal) has to receive 1.1 electron volts in order to cause its valence electron (electron in the outermost shell) to move into the conduction zone.
A typical silicon PV cell is composed of a wafer consisting of an ultra-thin layer of phosphorus-doped silicon (N-layer with a negative character), which is placed on top of a thicker layer of boron-doped silicon (P-layer with positive character). These layers are connected by the P-N junction. When sunlight strikes the surface of the PV cell, an electrical field is generated, which provides momentum and direction to the light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load.
Flat-plate PV collectors contain an array of individual cells, connected in a series/parallel circuit and encapsulated within a sandwich structure, the front of which is glass or plastic. Unlike thermal collectors, the backside of the collectors is not insulated, because for best performance, they need to be cooled by the atmosphere. If this energy loss can be eliminated in new designs, the conversion efficiency could be much improved. Flat PV collectors can also track the sun by being tilted about their axis. Flexible thin film solar cell strips and collectors are also available[33].
Parabolic PV collectors combine the steam generation capability of the thermal collectors with direct electricity generation by PV cells. In the figure below the silicon solar cells, that are bonded to the coolant tube, serve to geverate electricity, while the high temperature coolant is used to generate steam.
Today the energy payback period[34] of PV collectors for thin-film PV systems is about 3 years and for multi-crystalline silicon PV systems about 4 years. As manufacturing techniques improve these payback periods are likely to drop to about 2 years. With a minimum life span of 25 years, the ratio of energy obtained to energy invested in the manufacturing of PV collectors is 10:1. This ration compares favorably for example with the energy payback of oil shale, which has a ratio of only 4:1.
The carbon dioxide emission payback period[35] of PV collectors is estimated to be 3 years.
The storage of solar energy is an important consideration, because storage is required to compensate for the diurnal, seasonal and weather-related variations in insolation. Therefore, in order to supply the continuous energy users without interruptions, the generated electricity must be stored. On small installations, such storage can be provided by hot water tanks or high density batteries. On mid-sized installations pumped hydro storage can be considered. For larger installations, the compressing of air into underground caverns has been suggested.
A better option is to eliminate the need for storage. This can be achieved if an electric grid is available in the area and it can take the excess solar electricity when not needed or can supplement the shortage of electricity when more is needed. For example, if the solar power plant is located close to a hydroelectric or fossil power plant, it is possible to increase or decrease the power plant's rate of generation as the availability of solar energy changes.
A favored method of storage is to convert solar energy into chemical energy (convert it into a fuel) and store/distribute it in that form as chemical energy. The carriers of this chemical energy can be gases, liquids or solids. In one process, high temperature solar chemistry is used, where mirrors concentrate the sun's rays on zinc oxide and vaporize it at a temperature of 1200 °C. The vaporized zinc is later condensed into a powder. This zinc can than be transported and when reacted with water vapor, will produce hydrogen fuel while recombining with oxygen back into zinc oxide[36]. This method of solar energy storage is not yet available commercially.
Chemical energy can also be stored in hydrogen. Hydrogen can be generated from ammonia, from the reforming of fossil fuels or by the electrolysis of water. Naturally, when made from fossil fuels, the carbon is exhausted into the atmosphere in the form of carbon dioxide, which contributes to global warming.
Hydrogen can be stored as high pressure gas, as cryogenic liquid or can be absorbed in solids such as in metal hydrides (sodium borohydride) and in metallic "sponges" (zirconium, platinum, lanthanum). Hydrogen is one of the means of storing solar energy in the chemical form, which allows it to be used as a fuel.
Before discussing the generation of solar-hydrogen (electrolysis), first the properties of hydrogen and its suitability as a transportation fuel will be discussed.
Hydrogen is stored as a liquid[37] (cryogenic) or as a gas compressed to some 350 to 800 atmospheres pressure (5,000 to 12,000 pounds per square inch). On a weight basis, the energy content of hydrogen is 3.4 times that of gasoline[38]. On a volume basis, hydrogen requires 3 times the volume of gasoline to store the same amount of energy. Hydrogen can also be stored in solids and these "reversible solid" storage processes are probably the safest, but their development is still in the experimental stage. Today they are capable only of storing small amounts of energy.
Because of its lower volumetric energy density, when hydrogen is used as fuel for transportation, the volume of the hydrogen fuel tanks need to be 3 times the size of today's gasoline[39] tanks to provide the same driving range. Actually, the volume of the hydrogen tanks can be somewhat smaller than 3 times, because hydrogen engines are more efficient[40] than the gasoline burning ones.
High pressure hydrogen tanks are made of carbon fiber. Cryogenic (liquid) hydrogen tanks are double walled with the space between the walls evacuated to provide good thermal insulation.
If, instead of hydrogen fuel, electric cars[41] with battery storage are used, the batteries can be recharged at electric filling stations. In the future, these electric filling stations are likely to also have the capability to provide both gasoline and hydrogen fuels[42], as the automobile fleet of the next couple of decades is likely to become a mixed one[43].
The energy consumption of compressing hydrogen is about 16% of the energy content of the gas, if a single stage compressor is used and 12% if multistage units with intercoolers are utilized. The
energy cost of liquefying hydrogen is about 30% of its energy content[44]. In addition, when storing liquid hydrogen, some of the liquid in the tank will vaporize due to heat infiltration (hydrogen boil-off), which will reduce the volume available for storing the liquid. The production capacity of liquefiers serving NASA's Space Shuttle (Air Products) is 35-40 tons/day.
Because of its lower density, the transportation of hydrogen through pipeline requires more energy than does the transportation of natural gas. Transportation of compressed hydrogen gas by trucks is inefficient, because an empty truck (capable of holding several hundred atmospheres of pressure) will weigh almost as much as a full one. Its tank can hold only about 400 kilograms of hydrogen. For this reason, a busy gas station could require 10-20 deliveries of hydrogen gas a day, while if liquid hydrogen is used, a single daily delivery would suffice. This is a consideration in favor of transporting and storing hydrogen in the liquid form, although the energy cost of liquefying is additional to the energy needed to pressurize the gas.
Safety is another important consideration. During the last decades, hydrogen has been extensively used in the petrochemical, food and space exploration industries[45]. This experience has made hydrogen storage, transportation and handling reasonably safe. The design of hydrogen tankers and trucks is similar to the design of their counterparts used to transport LNG. From the point of view of safety, hydrogen has an advantage over LNG, because in case of a leakage, the high molecular weight gases, such as propane, will accumulate on the ground, while hydrogen will quickly escape into the atmosphere. Crash tests of automobiles with hydrogen tanks were conducted to prove this.
Some 98% of the bulk hydrogen that is produced today is generated from steam reformation of natural gas (methane, CH4) where methane is reacted with water vapor over a catalyst to form carbon monoxide (CO) and hydrogen. Actually, one can also use ethanol (alcohol), biomass, fossil fuels or organic waste to produce hydrogen by the process of "reforming". Naturally, this process also releases large quantities of greenhouse gases into the atmosphere.
Vegetation, including algae, while absorbing sunshine, also produces hydrogen from water and combines the hydrogen with carbon dioxide to produce glucose. As shown in the figure below, multiple energy sources and a variety of chemicals can be used to generate hydrogen, but solar or wind[46] based electrolysis (or ultrasonic splitting) of water are the only processes that are completely nonpolluting.
In 1820, Faraday discovered electrolysis by passing electricity through water and thereby generating hydrogen at the negative electrode (cathode)[47] and oxygen at the positive electrode (anode). Thus, electrolysis can be used to produce hydrogen from water while consuming
electricity. Plants and vegetation use a similar process. They use chlorophyll as a catalyst and the energy of the sun to decompose water into diatomic oxygen gas and hydrogen that is reacted with carbon dioxide to form glucose. Until the industrial age, the atmospheric concentration of carbon dioxide was constant, because the CO2 exhaled by the animals was consumed by the plants.
Electrolysis is an endothermic reaction that requires energy for its operation (blue arrow in the figure below):
H2O + (286 kJ of ENERGY) ↔ H2 + 1/2O2
As it is illustrated above, it takes the same amount of energy to split water into hydrogen and oxygen as the amount of energy that is generated by oxidizing hydrogen into water. The only difference is that because electrolysis increases entropy, not all the energy need to be supplied in the form of electricity. Only 237.1 kJ of electrical energy is needed to make a mole of hydrogen, because the surrounding environment will contribute the additional 48.7 kJ of thermal energy.
Water can be converted into hydrogen and oxygen by using electricity from a battery or from any other electricity source, including solar electricity. In nuclear submarines, the electricity is provided from nuclear power and the main reason for the electrolysis equipment in submarine applications is to produce oxygen.
When the electricity from a battery is replaced by electricity from solar collectors, "solar-hydrogen" is produced. One mole of water produces one mole of hydrogen gas plus a half-mole of oxygen gas, both in their normal diatomic forms[48].
The target set by the US Department of Energy (DOE) is to increase the efficiency of electrolysis (presently around 66%) to 75%, while eliminating the need for platinum electrodes. Efficiency is defined as the ratio of the energy contained in the hydrogen that is produced, divided by the energy it takes to produce that hydrogen. The DOE efficiency target has already been reached by some designs using new porous electrode materials.
When hydrogen fuel is burned, it emits no carbon dioxide, no carbon monoxide, no sulfur dioxide, no volatile organic compounds, nor fine particles. The only by-product of the combustion of hydrogen is water vapor. This formation of a mole of water (18 grams) also produces, 286 kJ[49] of energy. If this combustion takes place in a fuel cell (illustrated below), only 237.3 kJ of this energy can be recovered as electric energy output, while 48.7 kJ will heat the environment. Viewing the electrolysis and the fuel cell reactions as a pair, the enthalpy change is 286 kJ in both reactions, but in case of electrolysis the environment contributes 48.7 kJ heat energy while in case of the fuel cell reaction 48.7 kJ has to be dumped into the environment in the form of heat.
In an ideal (theoretically perfect) fuel cell, the energy content of the fuel is converted into electrical energy at an efficiency of 237/286 = 83%. This efficiency is much greater than the efficiency of the regular hydrogen combustion process. Although real fuel cell efficiencies are lower than this ideal value (about 66%)[50], they are much greater than the efficiency of fossil electric power plants[51] or internal combustion engines (25%).
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The various fuel cell designs are categorized according to their operating temperatures, electrode designs, electrolytes used and the type of fuel. Electrolytes can be acidic or alkaline liquids, solids or solid-liquid composites. Low temperature alkaline fuel cells (AFCs) were one of the first designs used in the US space program to produce water and electricity on spacecraft. Their disadvantages include that they are subject to carbon monoxide poisoning, are expensive and have short operating times.
Phosphoric acid fuel cells (PAFC) are considered to be "first generation" mature designs that are used in larger vehicles and buses. These are medium temperature (400 °F) units, generally available in the 60 to 200 kW size range. They can be 85% efficient when used to generate both electricity and heat, but only about 50% when generating electricity only. They are large, heavy and cost around $4000/kW.
Polymer electrolyte membrane (PEM) fuel cells (also called proton exchange cells) are suited for passenger vehicles. They operate at low temperatures (190 °F), provide high power density and are low in weight. Their byproduct is hot water and their size range is from 60 to 200 kW. They use a solid polymer electrolyte, porous carbon electrodes and platinum catalyst. Developers are currently exploring other catalysts that are more resistant to carbon monoxide poisoning.
In the larger sizes (250 kw to 3 MW), high temperature fuel cells are used in carbonate or solid oxide materials. Their operating temperatures range from 1200 to 1800 °F and their byproduct is high pressure steam.
In addition, the development of many other new designs is in progress. Once lightweight and low cost[52] fuel cells are available, they can generate electricity in solar hydrogen homes[53] or power electrically driven automobiles without causing any pollution. In electric cars, it is likely that fuel cells will outperform today's heavy and large storage batteries. Yet we do not yet know the final outcome of the battery vs. fuel cell race, because batteries are less expensive, their energy density is rising, their size is dropping, while fuel cells are still expensive.
The solar collectors are the first links in the chain of equipment that is required for the functioning of the solar-hydrogen energy economy. The efficiency of photovoltaic (PV) cell's range from about 8% for the amorphous silicon versions to 12%-17% for crystalline silicon designs. The efficiency of concentrating and reflected PV designs can reach 25% to 30%.
The first cost of crystalline PV collectors is about $3/Wp, while their installed cost is about $5-$6/Wp. When used in residential installations, the costs for an average home range from $40,000 to $60,000. The average capacity of these residential solar collector installations is 5 to 8 kWp[54]. Such an installation pays for itself in about 12 years, if it is partially financed by state support[55] and if the state requires the power companies to allow these installations to be connected to the grid, so that the excess power need not be stored in batteries, but can be sold to the power company and will be credited by them.
The unit cost of electricity generated by larger PV installations is about 20˘/kWh[56]. When generated by higher efficiency thermal solar plants, the electricity cost drops to 8˘ to 17˘/ kWh[57] This cost is competitive with the price paid for fossil generated electricity in some areas, but it is 1.5 times that in other areas. In case of large solar power plants, the energy supply of the area is usually coordinated among the power companies and state authorities. Both Israel[58] and China[59] are building large solar power plants at investments of about $2,500/m2 of collector area.
Solar collector systems in the past were purchased at prices based on their capacity expressed in $/Wp. Recently, in some states, one can purchase collector systems without an "up front" payment, just by signing a Power Purchase Agreement (PPA). This agreement states that the electricity generated by the system will be purchased for a negotiated price (in the range between 6 to 30 cents/kWh[60]) for an agreed upon time period (5 to 25 years).
After the solar collectors, electrolysis is the next link in the chain of equipment used in the solar-hydrogen process. The electrolyser efficiency is around 66% and the target set by the United States Department of Energy (DOE) is to increase that to 75%. The installed cost of smaller electrolysis equipment is around $3,000/kW. This price drops substantially as the size increases.
The efficiency of compressing the generated hydrogen is from 84% to 88%. It takes about 16% of the energy content of the gas to compress it, if a single stage compressor is used and 12% if multistage units with intercoolers are utilized. The efficiency of the equipment used in liquefying the compressed gas is about 70%.
In addition to the costs of the solar collector, electrolyser and hydrogen handling equipment, there are also transportation, storage and infrastructure expenses. Today, the cost of liquid hydrogen, made from natural gas is about $8/kg while hydrogen in the high pressure gas form is $25/kg. As a kilogram of hydrogen has the same energy content as a gallon of gasoline, - which in Europe is around $7 to $8 and in the United States is between $2 and $3 -, this price is not yet competitive. Hydrogen made by electrolysis from water, using fossil fuel generated electricity costs about $4.50/kg. As of today, solar electricity is more expensive than the fossil fuel generated, but its prices are coming down and therefore solar-hydrogen is expected to become competitive with fossil based.
To meet today's global energy consumption by solar energy, 3% to 5% of the area of the Sahara would need to be covered with solar collectors. The cost of doing that, plus the cost of the equipment associated with the generation, transportation, storage and handling of hydrogen, at today's costs is prohibitive[61]. Yet, the cost of inaction by 2020 is estimated - by Sir Nicholas Stern, former chief economist at the World Bank - to be 20% of the global GDP[62] and that cost is rising. As a comparison, it is estimated[63] that just to update the old refineries and to modernize the global oil infrastructure would cost $3 trillion.
On the brighter side, it is known that as new technologies mature and as their equipment start to be mass produced, their prices drop. In past years, computer performance improved by orders of magnitude every decade. Similarly, over the last decades, the cost of wind power generated electricity been reduced to one quarter of that generated by the first installations. Therefore, it is not unrealistic to expect that the costs of mass produced solar-hydrogen energy will also drop as their markets expand. Therefore, the cost of transition to a solar-hydrogen economy over several decades should be manageable.
The implications of a shift to the solar-hydrogen economy are profound. The world would be freed from the dependence on fossil fuels, thereby ending not only global warming but also the geopolitical nightmare that has preoccupied national security planners for the last 50 years. This systematic transition can begin slowly, but later is likely to gain momentum. The pace and direction of energy use are determined not just by technological developments, but also by social, economic and environmental forces and by the response of industries, governments and of society as a whole. The support of the general public can best be gained by providing actual cost and performance data from operating demonstration plants.
The time for holding conferences and for writing articles is over. It is time for action. It is time to build complete solar-hydrogen demonstration plants. Once built, they will provide reliable cost and efficiency data and later the components of the equipment chain can be optimized until they are both reliable and cost-effective.
The figure below identifies the main equipment blocks of a solar-hydrogen demonstration plant. These packaged units should eventually be mass producedto generate both fuel and electricity in various sizes[64] . The smallest of the standardized hydrogen generator units, the 1,000 kg/yr capacity one would be designed to serve individual households, the 10,000 kg/yr unit for schools, hospitals and other institutions, the 100,000 kg/yr package to serve small communities, while the 1,000,000 kg/yr plant would become the power plant of the future.
The figure below lists the approximate present efficiencies of the equipment blocks and gives their hydrogen and electricity production costs today. The cost of solar electricity is between 10˘/kWh and 20˘/kWh. The hydrogen equivalent of a gallon of gasoline costs from $4.50 to $8.0. One of the goals of building the demonstration plants is to drastically reduce these numbers.
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20˘ per kWh |
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Low press. H2 gas |
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Liquid H2 @ $5/kg |
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SOLAR ENERGY is converted to electric energy (photons are converted to electrons) |
Eff.= 15% |
ELECTROLYSIS Converts electric energy to chemical energy, which is stored in hydrogen |
Eff.= 66% |
HYDROGEN is compressed and liquefied so that its chemical energy can be stored and transported |
Eff.= 35% to 62% |
Combustion of H2 in fuel cells & power plants converts chemical energy into heat, work & electricity |
The main equipment blocks of the solar-hydrogen energy economy
(The total global energy consumption can be collected on 3% of the Sahara)
With today's technology, only a very small portion of the solar energy falling on a unit area can converted to useful energy for our homes and industry. This is because of the low efficiencies of the equipment blocks in the chain (see tabulation below) and because of the losses in the many conversions as the solar energy is converted to thermal, electric and chemical forms before it is finally applied to useful purposes.
The goal of building these demonstration plants is to obtain hard numbers, so that the debate over the costs of the solar-hydrogen economy can be closed. The other goal is to identify and eliminate the bottlenecks, optimize the processes and generate standardized packages. Once these standard packages are available, an international effort should be initiated to minimize the generator costs through mass production and free market competition.
Once the generator units are on the market and can be distributed around the world, not only the transition from oil to solar energy will start, but mankind's confidence in the future will also return, just as did Europe's confidence in its future by the Marshall Plan. To do this, the best scientific talent of the world should be mobilized. Past efforts like the Manhattan project and the trip to the Moon prove that this is doable and the consequences of inaction should convince all that this must be done.
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Solar Hot Water Systems, Roof Collectors |
50% to 70% efficiency, about $25,000/home, state support 0% to 75% Suppliers: Many |
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Concentrating & Reflected Photovoltaic (PV) |
25% to 40% efficiency, Installed cost: ($5.0 -$7.0)/Wp or about $4,000/m2 , Generated electricity cost: 20˘/kWh Suppliers : Spectrolab, Amonix, Suntech, Solarex, SunPower, H2GO/Solfocus, Energy Innovations |
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Thermal: Direct Steam Generator (DSG) |
20% to 30% efficiency, Installed cost: ($3.0-$4.0)/Wp or about $3,000/m2, Generated electricity cost: (12˘-20˘)/kWh Suppliers: Schott, Luz, Solel Co. |
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Solar-Thermal Electric Generating Systems (SEGS) |
10% to 27% efficiency, Installed cost: ($2.50-$3.0)/Wp or about $2,500/m2, Generated electricity cost: (8˘-17˘)/kWh Suppliers: Kramer Junction Op. Co., Suntech, Schott, Luz , Solel Co. |
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Crystalline Silicon Photovoltaic (PV) |
10% to 17% efficiency, Collerctor cost: $3.20-$3.50, Installed cost: ($5.0-$7.0)/Wp or about $3,500/m2, Generated electricity cost: 20˘/kWh Suppliers: Sanyo, SkyPower, SunEdison,Suntech, BP Solar, Isofoton, Photowatt Int., Schott Solar, TATA BP Solar, Webel-SL Energy, SunPower |
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Thin Film Amorphous Silicon PV for roofs, tents, etc. |
6% to 8% efficiency, Installed cost about $60,000/home minus state support, Generated electricity: 10˘/kWh , Suppliers: For homes: PlugPowerGenCore, Others: UniSolar, Konarka. |
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Solar Upward Tower |
About 5% efficiency, Installed cost: ($2.0 - $4.0)/W. Power generation per square meter of area: 5-6W. Supplier: EnviroMission |
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Electrolysers: Solar-Hydrogen Generation from Water |
Present efficiency 66%, DOE target: 75%, Installed cost for small units: $3/W, for large ones ($1.0-$1.5)/W, Energy consumption: 32.9kWh/kg, Suppliers: Proton Energy Systems, H2Gen Innovations, Teledyne |
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Hydrogen Compression and Condensation Equipment |
Compression efficiency is 84-88%, liquefying: 60%-70%, combined total: 45%-60%. Energy cost of 1 kg of liquid hydrogen: 6 to 12 kWh Suppliers: Linde, Air Products and Chemicals, Praxair, |
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Fuel Cells Burning Hydrogen Fuel at the Users (AFC, PAFC, PEM) |
Efficiency in generating electricity: 45% to 60%, efficiency if both heat and electricity is used: 83%, Installed Cost is ($3.0 to $4.0)/W Suppliers: PlugPowerGenCore, FuelCellEnergy, G.E., Nuvera, UTC |
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Internal Combustion Engines on Various Fuels |
Gasoline: 25%, Diesel: 35%, Hydrogen: 38% |
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Fossil Power Plants of Various Designs |
Sub-Critical: 36%-38%, Super-Critical: 42%-48%, Combined Cycle: 55%-60% |
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Solar-Hydrogen Generators of Various Sizes |
Efficiency = (Energy in liquid hydrogen)/(Energy from solar collectors) Generator sizes in kg/yr of hydrogen. 1,000 to 1,000,000: 22% to 33% Today's cost of hydrogen is $5/kg in the USA and $8/kg in Europe |
Prepared by: Béla Lipták, former adjunct professor of Yale University, editor of the Environmental Engineer's Handbook, recipient of ISA's Life Achievement and Control's Hall of Fame awards.
[1]The fossil power industry is developing a variety of carbon dioxide recapturing and storage processes. An example is the chilled ammonia process that takes the carbon dioxide from the flue gases, compresses and condenses it before injecting it as a liquid into the ground at some 9,000 feet below the surface. The capital cost of this system is $800 million while the operating cost includes the energy cost equaling one third of the power plant's energy output.
[2]Emissions can be reduced by a) subsidising alternative energy sources, b) by imposing efficiency and carbon emission standards on products and processes or 3) by applying carbon taxes by placing a price on emitting greenhouse gases. In the European Union the carbon price for 2010 is 16 Euros per ton of carbon dioxide released. While these are steps in the right direction, they only slow, but do not stop global warming.
[3]The global yearly consumption of fossil fuels is: coal 5.5 billion tons, oil 33 billion barrels, natural gas 100 trillion cubic foot. The yearly electricity consumption is 15 trillion kWh. The cost of electricity is much more than what we pay for it, because the environmental costs of its generation are not included. This environmental cost is paid by all mankind and Sir Nicholas Stern estimated that if no changes occur, it will amount to 20% of the global GDP by 2020. (The Cato Institute estimates that 5% to 10% of the GDP is being lost now. http://www.cato-at-liberty.org/2006/11/03/global-warming-costs-benefits/ ) The global GDP is today 37 trillion dollars and is estimated to reach 50 trillion by 2020. 20% of that amounts to 100 trillion dollars every decade and rising.
[4]In February 2007,
the Intergovernmental Panel on Climate Change reported with 90% confidence that
human activity is the main cause of global warming. Later in the same month the
UN Foundation predicted a rise of 11°F in global temperature by 2100 and
recommended to ban building on land less than 39 inches above sea level and ban
the construction of conventional coal fired power plants. Global temperature is
already the highest since the Middle Ages and it is estimated that by the end
of the century, sea levels will rise by some 23 inches.
The Kyoto treaty calls for greenhouse gas emissions to be reduced by 5% under
the 1990 level, the EU aims for an 8% reduction by 2012 and 20% by 2020, yet
today they are still rising. California will reduce greenhouse gas emissions
by 25% and England by 26% to 32% by 2020.
The yearly release of carbon dioxide is 27 billion tons, it has already caused
0.6 °C (1.1°F) rise in the global temperature as the atmospheric concentration
of carbon dioxide increased from 280 to 380 parts per million (ppm). If this
release continues, it will reach 550 ppm by 2100 and the global temperature
will rise by 2°C to 6°C (3.5°F to 11°F). The last time such temperatures were
reached occurred over 100,000 years ago and would cause the sea level to rise
by 7" to 23". This estimate does not include the effect of the melting of ice
at the poles. The rising carbon dioxide concentration of the atmosphere also
reduces the pH of the oceans. The release of methane is also rising. About 10
teratons of carbon (tera = 1012) are stored in the frozen methane hydrates of
the arctic regions, which will also be released, if the ice melts.
[5]This report by 2000 scientists organized by the UN predicts cultural and social disruptions, loss of wetlands, bleaching of coral reefs, acidification of oceans, widespread water shortage and starvation.
[6]The ultimately recoverable global oil supplies are estimated to range from 3.3 to 4.8 trillion barrels. Of this, 1.08 trillion has already been produced, 1.66 trillion is in conventional reserves and the rest can be obtained from oil shale or through the use of enhanced recovery methods.
[7]Q (Quad) equals one quadrillion (1015) BTUs of energy. One Q of energy is equal to the yearly energy produced by 33 nuclear power plants or the energy content of 10,000 supertankers of oil, 400,000 rail cars of coal or 28 billion cubic meters of natural gas. One Q approximately equals one exajoule (eJ) or 0.293 terawatt-hours (tWh). FYI: kilo = 103, mega = 106, giga = 109, tera = 1012, peta = 1015, exa = 1018.
[8]A British Thermal Unit (BTU) is the energy required to increase the temperature of one pound of water by one degree Fahrenheit at room temperature.
[9]Presently over 400 nuclear power plants are in operation. In the Unites States no new plant was built since the 1970s, but in 2006-2007 some twenty(20) permit applications been submitted. All existing nuclear plants are provided with analog controls. Mankind has no experience with digital automation of nuclear plants.
[10]These sources include hydroelectric dams, wind turbines, solar cells, geothermal, wave or tidal power, biomass, methane from rotting trash, manure or landfills. The European Union requires that its members increase the proportion of renewable energy use from 5.3% to 12% by 2010 and to generate 22% of their electric energy from renewable sources by that date. The EU also requires that the bio-diesel content of their diesel fuels reach 5.75% by 2010.
[11]The cost of wind turbine generated electricity is 4 to 6 cents/kWh and dropping. If fully exploited, Europe could meet 30% of its electricity needs by wind power.
[12]Reference: 2007 Solar Energy - Complete Guide to Solar Power and Photovoltaics, Practical Information on Heating, Lighting, and Concentrating, Energy Department Research (Two CD-ROM Set) (CD-ROM) by U.S. Government
[13]In addition to other pollutants such as NOx, SO2 and particulates, the generation of each kWh releases from 270 to 1050 grams of carbon dioxide into the atmosphere.
[14]Sir Nicholas Stern, was a distinguished development economist and former chief economist at the World Bank.
[15]The average American household releases about 20,000 pounds of greenhouse gases a year. Since 1990 American emissions rose by 18% and Chinese by 77%. The profit incentive can help reducing these emission if a carbon tax is applied. Because Chnese economy is three times as "carbon intensive", dollar for dollar, more reduction could be achieved, if the investments were made to improve Chinese power plant performance.
[16]British Petroleum (solar energy), Shell Oil (PV, hydrogen, wind power, biomass), Toyota (hybrid cars), General Electric (fuel cells, micro-turbines), BMW (hydrogen fueled internal combustion engine) and others.
[17]Landolt-Börnstein - Group VIII, Volume 3C "Renewable Energy" published by Springler Berlin, Heidelberg, DOI 10.1007/b83039, 2006
[18]The efficiency of solar hot water systems is 50% to 70%, the efficiency of solar-thermal-electric generating systems (SEGS) is around 20% (DSG - direct steam generation is superior, over 30%), and future installations, such as dish concentrators driving Stirling heat engines, which are being installed in Southern California, are expected to be more efficient. The efficiencies of conventional photovoltaic (PV) collectors range from 8% to 17% (Sanyo), while Fresnel lens type PV concentrator systems have reached 26.5% (Amonix, Inc).
[19]Assuming that the collector efficiency is 15%, the yearly solar energy reaching each square meter of collector area is 3,000 kWh, knowing that a square kilometer (km2) is a million square meters and that each kWh of energy equals 3413 BTUs, the collector area needed to generate each Q of electric energy is about 666 km2. Therefore, to collect the 400 Q which is presently used by mankind, 266,000 km2 needs to be covered by solar collectors. Because the area of the Sahara's is 9 million km2, about 3% of it's area would need to be covered to supply the Global energy need, if the energy was not converted to hydrogen and about 5% if it was stored in the form of chemical energy (hydrogen).
[20]The Sahara covers 1.6% of the total surface area of the globe (land on the planet occupies 150 million km2, the oceans occupy 361million km2 ). Therefore, including the oceans, the total high insolation area on the planet is more than 25 times that of the Sahara and more than 500 times the total available area of high insolation.
[21]In the north central USA, the yearly insolation is between 1000 and 1500 kW/h-m2. The efficiency at which this energy can be collected is as follows: Flat water heaters convert that energy at an efficiency of 60%-70%, while photovoltaic (PV) convert it with an efficiency of 10% to 17%. Using concentrated sunlight, Spectrolab demonstrated the ability of a photovoltaic cell to convert 40.7% of the sun's energy into electricity. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, Colo., verified this milestone achievement.
[22]A well insulated house in the north east United States uses about 1000 gallons of oil (150 million BTUs = 44,000 kWh) a year for the purposes of heating and hot water.
[23]The nations with the largest installed capacity of solar collectors are: China (36 gW - gigawatt), Japan (9 gW), Turkey (7 gW), Germany (3.5 gW), Greece (3.5 gW),….USA (1.5 gW). On a per capita basis, the leading users of solar energy are Cyprus, Israel and Greece.
[24]The concentrator designs include parabolic troughs, parabolic dishes, central receivers and Fresnel lenses. This last design uses refraction instead of reflection,
[25]Tracking the Sun increases the amount of energy collected by 30% to 40%.
[26] At the University of Nevada, such a new process is beingdeveloped, utilizing a new material made up of billions of nano-tubes. As water is passed through them, ultrasonic waves, which are generated by sun light cause the water to be broken down into hydrogen and oxygen. A small-scale reactor is currently in operation. According to the inventors, if successful, this process could yield hydrogen at the gasoline energy equivalent cost of about $1 gallon.
[27] This is one of nine solar electric energy generating plants at Kramer Junction, California. The individual plant sizes vary from 30 MWs and up, having a total capacity of 354 MWe. (photo courtesy Kramer Junction Operating Company). In this particular installation, the hot oil circulates at 400 °C (752 °F), but there are higher temperature installations also. One advantage of the SEGS design is that the solar energy can be conveniently stored in thermal storage and used as needed to compensate for diurnal, seasonal and weather related changes as insolation varies. Several computerized control systems serve to optimize the positioning of thousands of mirrors to accurately track the trajectory of the sun and thereby maximize the collected energy. One such early installation was controlled by a Beckman model MV-8000 DCS system (Beckman today is Fisher-Rosemount).
[28]The Spanish Colonel, Isidoro Cabanyes first proposed it in 1903, while the first patent for this design was applied for by Robert E. Lucier in 1975.
[29]In 1982 a working model was built in Ciudad Real, south of Madrid, Spain. This project was funded by the German government. The chimney of this model had a 10 meters (33') diameter and was 195 meters (640') tall, while the diameter of the canopy was 244 meters (800') diameter (about 11 acres or 46,000 m2. This prototype operated for 9 years and reached a maximum production of 50 kW.
[30]This year, construction will start on the world's first commercial plant in Australia. The two mile diameter canopy of this 50 MW power station at Tapio, will be 2.4 meters (8') tall at the perimeter and will rise to 15 meters (50') at the center, near the tower. The tower will be 79 meters (260') in diameter and 488 meters (1,600') in height. It is anticipated that this power plant will meet the needs of 100,000 homes for electricity. The plant is expected to be government financed at a cost of $75 million.
[31]The plant in China will also be designed by EnviroMission, but will be larger, consisting of a 38 km2 canopy and a 1 km (0.62 mile) tall tower to serve 200,000 homes with electricity. The 200 MW plant will abate about a million tons of greenhouse gases and will cost some $800 million.
[32]According to the International Energy Agency (IEA) 40% of all the PV installations today are in Germany and 13% in the United States. In Germany, the power companies buy back the generated electric power at a rate secured for 20 years. This is called a Feed in Tariff (FiT) program. The magazine Solar Generation reports (Sept. 2006 pp.24), that the total solar energy generation commitment in the USA by 2020 is 7.3 GW. Of this total, California is committed to 3 GW and New Jersey to 1.5 GW.
[33]UNI-SOLAR® roofing made from a thin film of amorphous silicon on plastic generates clean solar electricity to power homes or commercial buildings. Konarka produces plastic solar cell strips, which are like photographic film and can be embedded in cell phones, laptops or can be used as tents, which provide a kW of energy to power fans, lights, radios or laptops.
[34]The energy required for manufacturing, expressed as the time period required to collect the equivalent amount of solar energy to that which was needed to produce and assemble the particular PV collector and its support structure.
[35]This is the time required to compensate for the carbon dioxide emission that occurs during the manufacturing of the collectors, - if the PV collector is manufactured by the use of fossil fuel generated energy (400 kg CO2 per square meter of collector) - by the emission avoidance, which the energy generation by PV collectors will result in.
[36]A pilot plant jointly funded by the EU, the Paul Scherrer Institute (PSI) and the Swiss Federal Institute of Technology of Zurich (ETHZ) has successfully demonstrated this process in a 300 kW pilot plant at the Weizmann Institute of Science (WIS) in Rehovot near Tel Aviv. The plant produced 45 kilograms of zinc per hour.
[37] At atmospheric pressures hydrogen condenses at -423 °F (-217°C).
[38]Liquid hydrogen weighs 0.59 pounds/gallon and the energy content of one gallon of gasoline equals the heating value of 3.58 gallons of liquid hydrogen. The heating value of a kilogram of gasoline is 39,600 BTU (41.8 mJ), while the heating value of a kilogram of hydrogen is 134,616 BTU (142 mJ).
[39]A typical passenger car has a range of 575 miles and is provided with an 18 gallon tank while an 18 wheeled semi-truck has a 750 mile range and requires two 90 gallon tanks.
[40]At cruising speed, the efficiency of gasoline engines is 25%, of diesel engines 35%, while the internal combustion type hydrogen engine's efficiency is 35% and the fuel cell type is 45% to 50%.
[41] Ford Motor leased some 300, 150 mile range electric cars in California, where electric refilling stations are available, but later, -without a clear reason -, recalled these cars and sold them in Norway.
[44]At atmospheric pressures hydrogen condenses at -423 °F (-217°C). In order to increase this condensing temperature, the pressure of the gas is increased. After it has been compressed, the high pressure gas is cooled by a heat pump, which condenses it. The efficiency of this compression-condensation process ranges from 35% to 60% as a function of the refrigerant used in the heat pump. One of most efficient refrigerants is a mixture of helium and neon (Quack). The energy consumption of liquefiers range from 5 to 12 kWh/kg H2.
[45]Today, the United States is safely using 9 billion cubic feet of hydrogen a day in the petrochemical, food and rocket propulsion industries.
[46] Such systems are in operation in Minnesota, in Canada at Prince Edward Island, in Norway at Utsira island and at Hovik. The "Wind2H2 Project" in Boulder, Colorado links wind turbines to 5 kW PEM Proton Energy and 50 kW alkaline Teledyne water splitters, generating 20 kg/day of hydrogen, which is stored at 3,500 PSIG.
[47]96,484 coulombs (Faraday's constant) are required to deposit one mole of any material at the cathode of an electrolytic cell. Therefore it takes 237.13 kJ of electricity to synthesize one mole of hydrogen (kJ = 0.948 BTU). To this process, at typical ambient temperatures, the environment contributes 48.7 kJ of thermal energy per mole of hydrogen for a total of 286 kJ. The weight of one mole of hydrogen is 2 grams and the energy content of one gallon of gasoline equals the energy content of about 500 moles of hydrogen. The electricity needed to obtain the hydrogen equivalent of the energy of one gallon of gasoline is: [(237.13 x 500 x 0.948)/3,413)] = 32.9 kWh
[48]IMAGE SOURCE: "Chemistry in Context" Wm C Brown Publishers, Dubuque Iowa, 2nd edition, A project of the American Chemical Society, ed: A. Truman Schwartz et al., 1997, Chapter 5 "The Wonder of Water"
[49]One kJ (kilojoule) equals 0.948 BTU or 0.239 kilo Calories or 0.278 Wh.
[50]The efficiencies of single cycle units range are from 47% to 50%, the efficiency of combined cycle units is about 60% and if the generated heat is also recovered (directly or in the form of hot water or steam), the total efficiency can reach 90%.
[51] Sub-critical fossil fuel power plants can achieve 36-38% efficiency. Super critical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 30 MPa and dual stage reheat, the efficiency can reach about 48%. Fossil power plants can also use gas turbines, sometimes in conjunction with a steam boiler "bottoming" cycle. The efficiency of a combined cycle plant can approach 60% in large (500+ MWe) units. Nuclear power plants generally cannot reheat process steam due to safety requirements for isolation from the reactor core. This limits their thermodynamic efficiency to the order of 34-36%.
[52]Todays fuel cell costs in the 2 to 4 MW size range are from $3000 to $3500/kW.
[53]At Kingston Point, NY, an 800 ft2 solar-hydrogen home, built by the New York Institute of Technology (NYIT) is powered by a 5 kW PlugPowerGenCore fuel cell.
[54]These numbers increase if swimming pool or waterfall pumps and similar equipment also require power. The amount of solar electricity generated in most of Europe and most of the USA is about 90% of the amount generated in the southern regions. Therefore the capacity needed is 10% less in the South. The installations are usually sized to cover the total yearly electricity use of the home, so that the electricity bill will "zero out" at the end of the year. The yearly energy bill of an "average" household in the north central United States is about $4,500 ($2,500 for heat and hot water, $2,000 for electricity.)
[55]The highest amount of support in Europe is paid in Germany and in the United States in California, about $25,000/household installation. In New York the state pays 49% to 70% of the cost, in New Jersey the support is $3,800/kWp and in Connecticut $25,000 per installation.
[56]The cost of 20 cents per kWh is based on collector costs of $2000/kWh and on 100 kWp or larger size units with life expectancies of 20 years and 5% interest on investment.
[57]At Kramer Junction, California, some 9 solar power plants, 30 mW and larger, are in operation today. Their combined capacity is 354 mW. The yearly insolation in the area is 2940 kWh/m2. Plant efficiencies range from 10% to 17% and their capital costs range from $2500 to $3500 per kWp. The cost of generated electricity drops as the size of the plants increase from 17 cents to 7.7 cents per kWh.
[58]The initial capacity of the thermal solar power plant in the Negev is planned to be 150 mW and it is estimated to cost $350 million. The plant is planned to expand to 500 mW at a cost of $1 billion.
[59]In Dunhuang City (Gansu Province in China) the construction of a 100 MW, $765 million solar power plant has been approved. The plant will have 31,200 square meters of solar collectors at an installed cost of $2451/m2. Because in the area, the sun is shining for 3,362 hours a year, assuming that the plant will run fully loaded when the sun is out and assuming that the electricity will be sold at 10˘/kWh, the value of the produced electricitywill be $33.6 million/year.
[60]This way, solar power is able to directly compete with grid based power. SunEdison in California, SkyPower in Ontario and New Mexico are selling their systems on this basis. Their clients include Staples, Whole Food Markets, California State University and the city of San Diego.
[61]The total cost of conversion to a solar-hydrogen economy could amount to several years of the today's global GDP. Naturally, this cost would be spread out over a transition period of about 50 years. It is expected that during that time period, the equipment efficiencies would improve and the unit costs of production would drop substantially.
[62]The global GDP today is 37 trillion dollars and is expected to reach 50 trillion by 2020. 20% of the 2020 GDP corresponds to $100 trillion every decade and that expense is rising.
[63]Estimated by Prof. Wolfgang Reitzle, president and CEO of Linde.
[64]From 10 kW units for private homes to 1 gW sized power plants.
© 2007 Béla Lipták :: Magyar Baráti Közösség
Utolsó módosítás: 2007/04/15 15:29:56.248 GMT-7
