France Pioneers Industrial Use of Solar Energy
By “Awake!” correspondent in France
UP TO the middle of the last century man burned wood to satisfy most of his needs for fuel and power. But with the advent of the industrial era, more and more energy was required to drive the increasing number of machines. So coal began to be utilized on a wide scale. In fact, by 1910 three quarters of mankind’s power needs were met by coal.
Around 1859 another type of fossil fuel, mineral oil (petroleum), began to be used. It was to have far more industrial uses than coal ever had. The invention of the internal-combustion engine gave rise to the increased development of motor vehicles of all kinds, such as cars, trucks and aircraft.
Increasing industrial use of coal and oil has played a decisive part in the pollution of the earth. The reason is that these fuels do not burn up completely. They release into the atmosphere great concentrations of gases—carbon monoxide and nitrogen oxides and sulphur oxides—as well as solid particles.
As in other industrial countries, pollution is on the increase in France. During restoration work on the Louvre in Paris, the stonework was found to have suffered considerably from the corrosive effects of atmospheric pollution. Some blocks of stone had lost seven centimeters (2 3/4 inches) of their original thickness. Today corrosion is eating away the masonry at the rate of three millimeters (over 1/10 inch) a year, 100 times as fast as at the beginning of the century!
In recent years nuclear energy has been introduced as a potential replacement for oil. However, its industrial use results in many difficulties. For one thing, there is a risk of radioactive contamination that could follow an accident. Additionally, there is potential danger to the ecology. It is feared that, as nuclear power stations become more numerous, the rivers and lakes will be ruined by thermal pollution. This is because, in order to cool its apparatus, a nuclear power station draws huge quantities of cold water out of a nearby river or lake. The heated water is then returned to its source. When the temperature of a lake or river is raised, the amount of oxygen in the water is lowered. This not only kills fish but fosters the growth of algae, which also consume oxygen when decaying.
These disturbing facts emphasize the need to find pollution-free sources of energy. The sun itself meets this requirement exactly. Solar energy, although intermittent and diluted, is so generously distributed over the surface of the earth that every square mile of land and sea receives several million kilowatt-hours daily. This type of energy is naturally abundant, which explains why a number of countries, including France, have undertaken to pioneer the industrial use of solar energy.
Exploiting Solar Energy
During a visit to Paris in October 1774, the English chemist Joseph Priestley told French chemist Antoine Lavoisier of an experiment during which he had heated mercuric oxide by means of solar radiation concentrated by a powerful lens. Lavoisier did the experiment again and concluded that atmospheric air is a blend mainly of two distinct gases, which he called “vital air” (oxygen) and “non-vital air” (nitrogen). Thus, as far back as the 18th century it was possible to produce high temperatures by utilizing solar radiation.
For decades researchers at the C.N.R.S. or Centre national de la recherche scientifique (French National Center for Scientific Research) have been following in Lavoisier’s footsteps. In 1946 at Meudon, in the suburbs of Paris, a first solar furnace was set in operation and different experiments were made at high temperatures (3,000 degrees Celsius, or over 5,400 degrees Fahrenheit).
However, as a result of research on simple furnace prototypes from 1949 on at Mont Louis, in the French Pyrenees, the Odeillo solar furnace was eventually developed. After a long period of perfecting and adjusting, it eventually became operational in 1970. Today France has a large solar furnace at Font-Romeu-Odeillo-Via, near Mont Louis, at an altitude of 1,600 meters (5,250 feet). This beautiful mountainous region enjoys exceptional sunshine, which enables the 1,000-kilowatt furnace to reach a temperature of 3,800 degrees Celsius (over 6,800 degrees Fahrenheit).
Various methods can be used to capture solar radiation, such as using panes of glass, which, working on the principle of a greenhouse, can easily generate temperatures approaching 100 degrees Celsius (212 degrees Fahrenheit)—the boiling point of water. This method is used mostly for domestic purposes, such as heating houses and heating and distilling water. If higher temperatures are required, the rays coming directly from the sun have to be concentrated by an appropriate optical device.
The higher the temperature desired on the spot where all the rays converge (the focal point), the stronger the concentration must be. Concentrating tens of thousands of reflections of the same light source onto a small area is no easy task because of the movement of the earth around the sun. The difficulty, however, has been overcome at the Odeillo solar furnace, which superimposes over 20,000 images on the focal point. This remarkable result is the fruit of long research.
The Solar Furnace
Basically the Odeillo solar furnace consists of three different elements: (1) flat mirrors, (2) a large parabolic reflector and (3) a tower housing the focal point. As indicated on the accompanying diagram, the sun’s rays hit dozens of flat mirrors and are thrown back toward the parabolic reflector, which, in turn, focuses the rays onto the focal point facing it in the tower.
The 63 mobile flat mirrors, each of which is made up of 180 flat panes of glass, are arranged in tiers along eight levels. Measuring 45 square meters (484 square feet) each, they are in alternate rows so as to avoid any shadow in the beam of rays directed toward the parabolic reflector. Owing to the rotation of the earth, the position of the sun in our sky is constantly changing. However, each flat mirror can follow the sun in its never-ending journey by means of optical and electronic tracking devices. The movements involved on the part of the mirrors are brought about by hydraulic jacks.
Supported by a 40-meter- (130-foot-) high and 54-meter- (177-foot-) wide concrete structure, the large, immobile parabolic reflector consists of 9,500 mirrors, each measuring 45 centimeters (about 18 inches). Each facet in this giant mirror had to be mechanically curved, oriented and adjusted, so that maximum concentration was obtained on the focal point. As already stated, the parabolic reflector receives solar radiation by means of 63 mobile flat mirrors.
All the rays from the parabolic reflector converge on the focal point. It is housed in a tower 18 meters (59 feet) away from the reflector. The resulting focal spot is approximately 40 centimeters (almost 16 inches) in diameter. The energy concentrated on this elliptical spot amounts to 1,000 kilowatts. The high concentration makes it possible to reach a temperature of 3,800 degrees Celsius (6,872 degrees Fahrenheit). This spot of high heat intensity is where various experimental devices are set up.
Advantages of the Solar Furnace
The solar furnace offers significant advantages over other types of furnaces. The following extract from a C.N.R.S. publication emphasizes one of its essential characteristics: “In basic research solar furnaces constitute an exceptional means for carrying out experiments requiring between 1,000 and 3,800 degrees Celsius [approximately 1,800 to 6,800 degrees Fahrenheit] in conditions of extreme purity.” This is because the solar furnace allows processing at high temperatures by concentrating the heat rays on the materials to be processed, rather than by melting them down in a crucible, which is often the case with high-frequency electric furnaces.
The Odeillo solar furnace makes it very easy to melt refractory oxides, that is, oxides that melt only at very high temperatures (over 2,000 degrees Celsius or 3,600 degrees Fahrenheit), as well as special metallic alloys, which, too, are refractory.
Solar furnaces are also very convenient to use. They can be put into operation quickly and simply. Furthermore, they do not have such drawbacks as the bombardment of electrons that occurs in certain heating systems requiring that the materials be vacuum processed. Finally—and this is far from being negligible—the thermal energy available at Odeillo is obtained with practically no operating costs.
The Solar Power Station
A milestone in the field of solar energy was reached on November 19, 1976, when, for the first time ever, a solar-thermodynamic power station supplied electricity to the French national electric power system.
Simply put, this experimental solar power plant works in the following way: The temperature of a thermal fluid called “gilotherm” is raised to 335 degrees Celsius (635 degrees Fahrenheit) in a boiler placed on the focal point of the Odeillo complex. By means of a storage unit and three exchangers, this fluid supplies steam at 270 degrees Celsius (518 degrees Fahrenheit). The steam then propels a turbo-alternator, which produces electricity.
Near Marseilles, in the south of France, tests are being made on different types of mirrors. After pioneering in this field, France is considering the setting up of a one-megawatt prototype and aims at a range of 10 megawatts for the year 1980.
Future Applications of Solar Energy
The French newspaper Le Monde emphasized the immense field of application of solar energy for industrial use in these terms: “Diffuse and cheap, solar energy seems to be quite adapted to the needs of the lesser-developed countries. . . . It appears to be particularly appropriate for pumping water in isolated areas. In Latin America and Africa, the water needs for several villages are now covered by pumping stations using simple and reliable [solar] appliances which can for the most part be made locally, and which progressively become competitive, compared with those that rely, as most do, on Diesel engines.”
France has signed solar cooperation agreements with Brazil, Iran, Egypt and Algeria. As noted in the magazine L’Express, “For once, the southern countries are at an advantage, for it is there that solar energy can first be applied and improve its competitiveness before conquering the foggy industrialized north.”
Arab nations, such as Saudi Arabia, would like to cooperate in research on solar energy. French technology is in a position to respond to Saudi Arabian proposals, for, according to M. Jean-Claude Colli, French delegate to the Department of New Sources of Energy, “[France is] now practically the only nation offering solar electrical power plants for immediate operation.”
The 1978 French budget for new sources of energy rose sharply. Solar energy expenditures doubled. These efforts show that energy problems can be progressively solved by wise use of clean energy sources, such as the sun, wind, flowing water and ocean tides. Man really does not have to ‘ruin the earth’ to satisfy his growing energy needs.—Rev. 11:18.
[Diagram on page 17]
(For fully formatted text, see publication)
Sun’s rays
Parabolic reflector
Flat mirrors
Focal point