back on our present error by basing the activity of tomorrow’s world on only one energy source, even though it be twofold (uranium and seawater). The precise theme of this symposium is to explore the feasibility of a solar energy source capable of replacing the largest nuclear power plants presently projected for construction: 5 to 10 GW. During a recent symposium on innovation, I was led to define the term as follows: “Innovation normally consists of deliberate, daily technical progress, sought after and not undergone; in exceptional instances, it is the putting into practice of a new idea or invention. And I would add that to innovate is to desire to surpass routine, to progress, to refuse to remain passive when faced with the evolution of new techniques, but it is also to be conscious of the risks one runs in venturing off the beaten track.” A geostationary satellite system project that aims at collecting solar energy, transforming it, sending it to earth where it will be received, transformed a second time, and connected to energy distribution networks, constitutes a clear and precise example of innovation as defined above. Is it not the search for technical progress — deliberate, not undeigone, far from the beaten track? In spite of its ten year existence, the fundamental idea is so new that it will take another decade before the final problem of the project’s feasibility can actually be tackled. For the moment, all ideas relating to the overall system or the multitude of subsystems that will compose it must be greeted with humility, then analyzed without destructive apnorism. This symposium is the first to take place outside the United States and the first to be specifically dedicated to the solar power satellite project. More jostled than other continents by the energy crisis, less accustomed to innovative risks than the United States, aged Europe — perhaps wiser and more steadfast in its lifestyle — can make an important contribution to the project’s exploratory phase. This is one of the reasons for situating the symposium in a European city whose space and aeronautical vocation make her worthy of such a reception. The objectives of the symposium, consecrated to the feasibility of this gigantic innovation, are derived.from the analysis of the traditional and “new” sources of energy that our planet conceals. Even if one concedes that the present crisis is immediate rattier than long-term, there still remains a critical passage of two or three decades. What are the prospects? SHORT AND MIDDLE TERM PROSPECTS These essentially vary according to the country. Geothermal science is an interesting possibility, previously exploited yet still rich in promise, although the decrease in temperature of the presently exploited sinkings’ outflow (2 to 3 °C in ten years) is already somewhat disturbing. We can hope to reach a stabilized temperature — but at what level? For, at the scale on which we operate when an outflow exists, the temperatures are still difficult to estimate (“a transitory state” between the static temperature — at zero outflow — and the balanced temperature of the well’s nominal outflow can last more than a decade). In this case, human wisdom must dominate the search for immediate competitivity with other energy sources . . . still too inexpensive to avoid drying up the geothermal layers. As far as is absolutely possible, the sinkings should only be exploited at a stabilized temperature outflow. The reinjection process, mandatory in some countries, also
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