Introduction

It is now over two decades that a major effort is underway to utilize energy from renewable sources. Visionaries considered very early this idea as an important challenge to the human society. It was relatively easy to reach this conclusion if only three deductions were made:

• The demand for energy will increase both with the population increase and by the rising standard of living;
• The reserves of fossil fuel are finite; irrespective of how large they are, they must be finite;
• The products of fuel mining, transportation and burning must affect the environment in many ways. It is quite possible that long before we shall use up the fuel reserves, the globe will turn into an uninhabitable place or a place much less hospitable. The very transitional process may inflict great inconveniences and very high costs.
  

The oil crisis gave a great impetus and the justification to search for alternative energy sources. A mixture of uncontrolled financial glut, search for power and fundamentalism of one kind or another, caught the developed world by the throat and helped to awaken at least some. The alternative use of coal gas, and even oil shale, put the upper limit to the simple blackmail by the oil producers. Gradually, some of the oil magnates invested in the developed countries, and thus, put some self control on their price policy. However, the public establishment gave at best a lip service to the problem. Worse than that, the utilities and large fuel suppliers have fought against any attempt to bring some progress. It is difficult to believe how much money and manpower was invested into proving that things are not nearly as bad as they look, that there are many doubts in anything that points towards the need for alternative energy sources. Special institutes and scientific journals were supported for the sole purpose of preventing progress. The allocation of means to the relevant studies became a matter of political association. Conservatives voted against the financing of a search for green energy. [1]

In the last few years, huge oil suppliers like “British Petroleum” and “Shell”, seemingly became the massive promoters of clean energy. Their whole activity is nothing more than a public relations thrust.
In an industrial-commercial society which is encompassed in the sole question of what would be the income in the coming quarter, it is difficult to expect anything else. Any innovative process in the field of energy requires a relatively high investment over a relatively long period of time. It cannot compete with speculative gimmick in the world of communication, which is commonly called “hi-tech”.
At the present, the awareness of the environmental damage inflicted by fuel burning has reached already the decision makers’ circles. The following basic know-how is not in doubt
anymore.

1. The source of oil or gas is finite. At present use levels, the reserves will not suffice to more than several decades. The coal reserves can probably reach over 200 years. In any case, within a decade or two, the maximum use of oil and gas is expected. [1]
2. There is a significant change in the atmospheric gas composition which correlates with significant climatic changes and other environmental effects which inflict our planet. The chances are extremely high that at least a major part of the change is anthropogenic. Moreover, it seems that if we could reverse the extent of fuel burning, we would stand a good chance to correct some of the damages. [2]
3. There are numerous other works that leave no doubt as to the effects of climate change and the increase in natural disasters damages that from the ’50 to the ’90 went up from 40 billion dollars a year to 400 billion dollars a year. Over 90% of the events had a climatic change as their origin.
4. An uneven distribution of the fuel resources and the extreme disparity between developed and undeveloped countries fuel consumption, both are a major source of the world instability and conflicts. In the following lecture, I wish to explain the reason why a breakthrough in the electricity market did not take place, despite relatively large investments. I also wish to present at least one technology which may, in all probability, make a this breakthrough in the energy market.

Brief survey of alternative energy source

The methods, to produce electricity from renewable sources, are divided into two large groups:

Group A: Methods, which require a collector of solar radiation.

Group B: Methods, which do not require a solar collector, but use some transformed product of the solar radiation.

Group A

Among the methods:

Solar thermal - Solar 1, Solar 2 and the Solar Tower of the Weizmann Institute, Israel. This method includes the concentrating mirrors, like “Solel” and Frennel’s Lenses.

Solar ponds - Different kinds.

Updraft chimney - A method developed by Prof. Schlaich in Stuttgart, Germany.

Photovoltaic method - Produces electricity directly from radiation.

Hybrid methods.

Group B

These methods which do not require a solar collector, utilize a secondary process which occurs in nature due to solar radiation. Among the members of this group are: Wind turbines; Biomass; Hydropower; Wave energy. The utilization of temperature differences in the ocean (OTEC - Ocean Thermal Energy Conversion). (See reference, No. [3], in the bibliographical list).

In the present paper, I wish to present to you another method of the second group, which does not require a solar collector. The new technology is called “Energy Towers” and utilizes hot and dry air in arid zones. There are other methods which are not exactly of solar sources, or even renewable, but are usually included in discussions on alternative energies. Among those: the utilization of tide, geothermal sources and fuel cells. Fuel cells are neither cheap nor necessarily renewable. Their classification depends on the source of gas, which is oxidized to produce electricity in the fuel cell.

It is interesting to note that the cheapest solar component of electricity from solar thermal methods is not less than 12-15cents per kWh. Moreover, it works only 6-8 hours during the day, unless some expensive storage method is devised. All solar thermal methods are economically at the upper limit of economic feasibility, using the principles of sustainable development to their utmost. However, the industrial and economic society have not recognized as yet the full range of communal external costs, as in tables 4.1 and 4.2 to justify their use without some ideological preaching. Furthermore, the communal external cost of natural gas is grossly underestimated due to the disregard of gas leakage. The present glut of natural gas also disregards the predictions that gas costs may soon be doubled or even tripled, and all the world’s reserves do not exceed few decades.

The developers of solar thermal methods argue that once the technology will be applied on a large scale, it would become much cheaper. This remains to be seen. It is interesting to apply a simple check of the economical limits. Let us assume that the overall efficiency of turning the solar radiation to electricity is 17%. As an example, let us assume the following:

• An area with 2000 kWh radiation per square meter per year;
• A total output of the solar component to be 340 kWh per year;
• A competition with existing technologies, which provide kWh for 4 cents;
• An addition of 1 cent per kWh as bonus for clean energy. Its meaning is that the maximum production cost should not exceed 340X0.05=17 dollars per year per square meter, assuming nearly a 9% annual return under the market conditions, the initial investment in the solar system should not exceed 190 dollars per square meter.
  

The question is whether the overall investment can be below this figure? It is doubtful. The fact that the solar thermal method requires 3/4 of the electricity to produce from another source, burdens the whole system unless it is using regular fuel. However, if the bonus for clean energy is in the order of 6 cents, then the permissible cost is 10 cents per kWh and the permissible investment increases to twice the amount, i.e. nearly 380 dollars per square meter, producing 340 kWh per year. Remembering that there are 8760 hours a year, then one square meter is equivalent to 0.039 average kilowatt. The investment per average kilowatt is then $9794. In reality, the projected investment for the cheapest solar thermal is in the order of $12000 per average kilowatt. Comparing with table 4.2, the projected investment is within a reasonable limit.
In conclusion, despite the fact that solar thermal is probably justified from an overall sustainable point of view, it will have almost a hopeless struggle with the existing economic system to become fully commercialized.
Photovoltaic cells are very expensive and the electricity reaches costs of 40 cents per kWh. Some argue[1] that the photovoltaic technology will never become economically attractive. One can repeat the same reasoning as with the solar thermal source. Trainer’s argument is that even if the cells themselves will be produced free of charge, just the frame holding the cell, will turn the technology too expensive. He mentions high energy to produce the equipment, which will require almost half the life’s energy production by the cells. There may also be some use of rare elements that will limit the use of the system, batteries for storing the electricity over night etc.
The Solar Updraft Chimney uses a solar collector to warm air, which then rises in a tall and large diameter chimney. It is easy to show that the electricity cannot possibly be cheaper than 25-35 cents per kWh, only because there is a use of a collector. Solar ponds for electricity also proved themselves far too expensive. It is very interesting to note that the earliest energy used by man and still being used today is solar energy without a collector. Among these methods are included, as mentioned above: wind energy, water energy and burning of biomass. These still make some 20% of the energy used for electricity today. Even more interesting is that among the sources of renewable energy those are still, by far, the cheapest. Wind energy cost in suitable areas can be reduced to some 5 cents per kWh or less. Hydroelectricity in large projects can be as low as 2.5 cents per kWh, and in small projects up to 8 or 9 cents per kWh. Biomass can be used to produce electricity in utilizing municipal and agricultural waste at 5-9 cents per kWh.

My idea was to use hot and dry air, which is provided day and night mainly by Hadley Cell circulation (1735). Credit must be given also to Dr. Philip Carlson a physicist of Pasadena, California. We have soon learned that he suggested the same principle and even patented it in 1975. Since, we have improved the effect to cost ratio by a factor of 7.

The principles of the Energy Towers

The energetic principle is very simple. It imitates the phenomenon of “wind sheer”. A tall and large diameter chimney will be erected. Water will be sprayed at the top. Part of the water will evaporate and cool the air. The cooled air is denser than the air outside the chimney. It will descend and come out through openings at the bottom (see figure 1). On the way out, it will move turbines and generators that produce electricity. Naturally, the downdraft of air keeps on sucking more hot and dry air. It is exactly the opposite of a regular chimney updraft with hot air. The basic thermodynamics has been worked out. The efficiency of turning the heat in the air into potential mechanical work was found to be proportional to the following:

Where:

T_max [K] - the outside air temperature near the chimney bottom;

T_min [K] - the outside air temperature near the top of the chimney;

C - nearly a constant, between 0.7 and 0.8.

Under the conditions of descending air, the relation in the right hand side of equation 1 is dry-adiabatic and nearly equals to H_C / 30000, where H_C is the effective height of the chimney [m]. This is a very small efficiency. For a 1200 m height - H_C, the efficiency H_C is (0.7X12/300)=2.8%, however, there is a great abundance of hot air.

Figure 1. The principle of the Energy Tower

A very fundamental question is whether the useful electricity exceeds the energy needed to pump up the water and spray it. There is no general answer to this question. However, it is easy to show that there will be a sizeable net deliverable electricity over very large areas around the globe. Let us note first that the net deliverable output N [Watt] can be expressed by the following:

Where:

E_C [Pascals] - the extra pressure of the air column under static conditions; As an example, due to cooling of 12 centigrade over 1200 m, E_C=527 Pascals;

E_P [Pascals] - the pumping energy including the product of water spray per cubic meter of air times the head of water, including elevation differences, height of the chimney, spraying head and head losses. For the above example, assume 8 grams water per cubic meter of air and an overall head of 1350 m. It leads to E_P=108 Pascals;

E_R[Pascals] - the recoverable mechanical energy due to water spray momentum, unevaporated water weight in the air column and end brine disposal. E_R was very material in obtaining optimal outputs. In the above example, a characteristic figure of E_P was 50 Pa. Summing up the above example E_net= 469 Pa.

As long as E_net is positive, a net electricity output can be obtained. An interesting general proof showed that the optimal net deliverable output is when exactly 1/3 E_net is spent as energy losses. Following is a typical division of the mechanical energy, under the climatic conditions and topography in the Arava Valley north of Eilat in Israel, and Aqaba in Jordan.

Typical performance of the Energy Towers

Figure 2 shows a typical performance of an Energy Tower as a function of the rate of spray of sea water. The lower curve of the net deliverable power has an optimum at around 8 grams of water per kg of air. The upper curve of the gross power is of great importance because it can be used to deliver more electricity at hours of high electricity demand, by simply storing some water at high elevation during hours of low electricity demand. In the energy field, this process is called “pumped storage”. It should be noted that a very sizeable part of the investment and fuel use are commonly required in order to meet these peak demands. The built-in capacity of the Energy Towers to perform of what is called “pumped storage” is of extremely high economical value.

Figure 2. Gross and net power vs. spray rate in grams of water per kg air

In table 1 we compare the electricity production costs from coal and natural gas as predicted for the years 2005 and 2010, using actual information from a dozen and a half OECD developed countries, and another half a dozen from other countries such as India and China.[4]

It is very significant to note that the cost of electricity production from the Energy Towers is lower than the characteristic average values of the two “work horses of the industry”.
The cost of electricity from the Energy Towers is even lower than the lower limit of costs from coal and gas at 5% interest rate. At 10% interest rate, only the lowest limit of costs from gas beats those from the Energy Towers.

The additional benefits

The additional benefits can be divided into three groups:

GROUP I Replacing other spending and avoiding penalties

1. Built-in capacity for pumped storage which under the Israeli grid conditions added up to at least 1.5 cents per kWh income.
2. Eliminating fuel taxes, CO₂ penalty or clean energy bonus, (probably 1-2 cents). It has been estimated that in most of the countries, items 1 and 2 will add up to 2-3 cents per kWh to the net revenue. After adding this income to the figures in table 7.1, there is no case in which the cost of the conventional technologies is below the cost of electricity production by the Energy Towers.

GROUP II Other products associated with the Energy Towers

3. Half cost desalination of sea water due to reduced investment and energy outlay - The saving in the seawater desalination was estimated to be up to 45% and the contribution to Energy Towers is up to 0.6 cents per kWh.

4. Elimination of salinity from major irrigation projects - The application can be in large irrigation projects like the Colorado River, Murray Darling River in Australia, the Orange River in South Africa or the Indira Gandhi Canal in India. The gain for the Energy Towers is 1-2 cents per kWh.

5. Large scale sea fish farming, with gains to Energy Towers of 0.25-1.25 cents per kWh.
6. Cooling of thermal power stations, with gains to Energy Towers of up to 4 cents per kWh.

7. Pre-cooling of air for gas turbines with up to 10% saving in the investment for the gas turbine (about 1% added output for one centigrade air pre-cooling).

GROUP III Benefits due to macro-economic factors with gains to the Energy Towers of up to 1/3 in the investment or 0.8-2 cents per kWh

8. Improved balance of payment.
9. Avoidance of increased fuel prices.
10. Avoidance of fluctuation in prices.
11. Avoidance of strategic dependence and spending.
12. Avoidance of local environmental damages.
13. Meeting the requirements of Kyoto Protocol to reduce the greenhouse gas emission to the level of 1990.

Groups II and III can add several cents per kWh additional income to the towers, however, they are not all realistic in every case.

Review and validation

The project development was done under a close follow up by the Israeli Ministry of National Infrastructures and the Israeli Electric Corporation. The exact comparison between the economy of coal and gas and the Energy Towers is somewhat more complicated and lengthy. However, the basic picture is clear enough and the basic conclusion does not change. So far, there have been no such competitive source of renewable energy and such a list of additional benefits.
An Israeli expert committee was nominated to review the project in depth. The development team was asked to write 18 different brochures detailing different aspects. Seven experts from the committee have mobilized other teams of experts to check the project specifics. The conclusions were:

a) All physical principles were proven and re-proven beyond any doubt;
b) The whole project can be realized by known and proven technologies;
c) There is a wide positive economic margin that justifies the advance of the project towards commercial realization.

A 13 volumes documentation of the project development up to the end of 1999 was prepared at the request of the Israeli Ministry of National Infrastructures, a result of some 100 man-year effort.
The Indian Ministry of Science and Technology showed interest in the project. After receiving material on the Energy Towers project, they have prepared nearly 100 top technical people and scientists to review it, covering all possible subsystems and processes.
An Israeli delegation was invited in India along with the author of this article. The delegation had to face nearly 70 of these top professionals. Questions were asked, a survey was given and discussions took place.
Few months later, the Indian Ministry addressed the Israeli Government requesting that India would cooperate with Israel in the commercialization of the project. A positive answer was given. A mutual steering committee is being formed to undertake the future steps.

The project potential

The source of energy is mainly the Hadlley Cell circulation which elevates heated air at equatorial belts, often shedding rain. The air cools at a rate which is less than one Kelvin per 100 m and close to 0.5 Kelvin per 100 m. The air is later transmitted north and south, and lowers back to the globe’s surface, between 150 and 350 north and south in two belts of arid land and high pressure. On lowering, the air warms up nearly one Kelvin per 100 m. From there, the air goes back to the equator at low pressure, gaining, on-route, humidity.
A very rough evaluation, assuming about 1% overall transformation efficiency to electricity, was made in order to estimate the potential amount of net deliverable electricity over land. It was found to be sufficient for 40-80 billions people if all will consume electricity at west European level. There are some 40 different countries where the Energy Towers could be erected. With some modern transmission lines, the electricity can be sent at a relatively low cost to 3000 km north and south, east and west. Thus, some 80% of the global surface could be provided from this source.

To illustrate: north Africa has the potential to provide the whole of Europe with clean renewable electricity. Furthermore, it is estimated that seawater desalination could be obtained with some 45% cost reduction or 38 cents per cubic meter. The overall volume of desalinated water could reach 10-20 times the Nile River. Thus, north Africa could become the food and energy store for Europe.

Another recent estimate of the global theoretical potential was recently carried out. The method was to compute the output of “Energy Towers” at 1200 m height and 400 m diameter, using satellite data on humidity, temperature and wind at 1200m above ground elevation; each Tower was given 400 square kilometers open sky for sufficient hot air imported by the Hadley Cycle. The result between 200 MW and 600 MW average net output from each Tower was theoretically 88600 Towers, providing 230000 X 109 kWh per year. Dividing by 5000 kWh per person for the whole global population, it shows the theoretical possibility to provide electricity at west European level to 46 billion people. At 5% discount rate, the electricity production cost varies between 1.7 cents per kWh (600 MW Tower) to 3.9 cents per kWh (200 MW Tower). At 10% discount rate, the cost varies between 2.5 cents per kWh and 6.4 cents per kWh.

Few points which relate to the climatic regime

First of all, it is the climatic phenomenon that produces arid areas with descending air that makes the whole project possible. The Energy Towers have an interesting positive feed-back. When the air is warmer and dryer, and when the need for water pumping and the air conditioning increases, the production capacity by the Tower also increases. We have identified 10 environmental problems involved with the erection of the Energy Towers. One of these problems is the emission of cold and humid air. It seems that at worse, this emission enhances the Hadley Cell circulation, and has also some positive effects on the local climatic conditions.
Another environmental problem created is the emission of a salt spray in the form of fine brine droplets. If we can produce 5-6 kWh per one cubic meter water spray of sea water, the salt spray amounts to 0.67-0.8 kg salts per kWh. The team has found a way to cope with this problem by early precipitation of the brine spray. This is obtained by enhancing successful collision between droplets to cause them to coalesce and eliminate droplet sizes smaller than 300 or 400 microns.

The largest part of the project development is within the realm of climate physics and climatic effects. The environmental effects created by the Towers including noise, vision, air traffic, salt water spills and birds, seem trivial compared with those environmental problems which are eliminated. In addition to the avoidance of fuel burning, the Towers help solving the water shortage problem and salinization problems. By helping sea fish farming, the Towers also help another major environmental problem. It is interesting to note that growing fish requires some 40% of the food required for cattle. This is another way to save a lot of water.

Conclusions

The Energy Towers is the first technology to produce electricity from renewable sources to beat economically the work horses - coal and gas. The only other technology competing with the “Energy Towers” is hydroelectric projects. Next are wind energy and biomass. All of them are within the economic range justified by the sustainable development principle.
Solar thermal projects are already approaching these limits, but not quite there. They are still more expensive by a factor of 3-5. The Energy Towers will be able to provide all the anticipated increase in electricity demand from now on.

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