• Hideo Matsuoka
• Makoto Nagatomo
• Patrick Collins

The general public are strongly hoping for some inspiring initiatives to be announced in the year 2000, to give them confidence that their political leaders are abreast of the rapid changes occurring in the world today, and well prepared to face the major challenges expected in the following decades. Ensuring future supplies of clean energy on a scale many times larger than today is perhaps the greatest problem, and is deeply interconnected with the problems of environmental pollution, economic growth, population growth and unemployment.

It is increasingly recognised that, as the technologies for utilising solar energy in its various forms continue to improve, they will contribute increasingly to world energy use. One of the candidate ways of using solar power on a large scale is to transmit power generated continuously from sunlight in space by orbiting satellites to the Earth's surface using microwave beams. This system was proposed more than 30 years ago, and since then the various technologies required have been developed to a point of readiness.

The start of a first pilot plant project to demonstrate the delivery of solar-generated microwave power from satellites in Earth orbit to users living on Earth would be an exciting, publicly visible demonstration of a new way of tapping the limitless, clean solar energy available to us. Such a real demonstration will also be far more convincing proof to engineers and managers from the electricity generation industry that the technology of this system is now mature than theoretical explanations or experiments performed in space.

A 10MW solar power satellite (SPS) pilot plant is being designed in Japan to operate in orbit 1100 km above the equator and provide the first ever supply of electric power for thousands of homes in some of the poorest regions of the Earth. In doing so it will also generate a mass of data on the system's operation, and provide a test-bed that electricity supply companies will be able to use to perform a range of experiments that they need to be convinced of the system's feasibility.

To date the authors have made field research visits to ten developing countries along the equator, meeting government officials and researchers, and visiting candidate sites for microwave power receiving antennas (rectennas) up to 1 km or more in diameter. All the countries visited have expressed keen interest in participating in the project, and more detailed case studies of each candidate rectenna site are being planned. It is highly desirable that the technologically more advanced countries should collaborate with the less developed countries near the equator to bring this project to reality.