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SOLAR ENERGY

Introduction

Some issues are daily fare in the newspapers, but solar energy, in its various forms, is not among them. From time to time in the past fifty years it has made the news, but usually in conjunction with an energy or environmental crisis. That was the case during the first oil shock, in 1973, and it is so today too, now that the public has become concerned about global warming and climate change.

But even when the papers do talk about solar energy, they find it hard to treat it in a reasonably complete way. Like so many other topical subjects, solar energy is a complex matter, but usually the amount of space it receives in the media is only enough for a summary description. Nonetheless, some statistical projections remain in people's minds. One that is often cited e.g., in a report by Shell Renewables, a division of one of the world's largest oil companies is that by the year 2050, one half of the energy used worldwide will come from solar and other renewable sources.

Back in 1952, a report prepared by the Paley Commission for U.S. president Harry Truman predicted a bright future for solar energy. Among other things, the Paley report estimated that 13 million solar homes would have been built by the early 1970'S just when the world was hit by the first energy crisis of modern times. But the prospects outlined in the report quickly dimmed. Many people think this was due partly to the Atoms for Peace initiative, announced in 1953, which led countries all over the world to start programmes for peaceful uses of atomic energy.

In the past few years, however, modern solar technologies have been penetrating the market at faster and faster rates, and an optimistic view of the sector's future seems fully justified.

Nonetheless, past experience should make us aware of the fact that the most optimistic view of the future of solar energy could be set at naught by the appearance of an important invention or by unforeseeable events. Predicting the future is especially hard when the world is changing as quickly as it is in our day.

Can technological developments and the transition to a culture that is more aware of the need to safeguard the environment help create a world powered by the sun's energy?

A technologically advanced world

The fast pace of technological development is one of the most significant characteristics of our time. Today it takes only a few months to achieve the same number of important inventions and discoveries that took decades, if not centuries, in the past. This trend is accelerated by globalisation, which in turn is accelerated by the ever-growing use of the Internet. Technological development helps raise standards of living around the world. Diseases that afflicted humanity for centuries have been nearly eradicated, and life expectancy has lengthened in most countries. But many problems have not been solved yet, and others are in the offing.

The two common factors that underlie many of the problems threatening our future are the fast growing population and the ever increasing consumption of resources driven by the diffusion of life-styles that have developed in industrialised societies and are emulated in much of the world.

Until the discovery of fossil fuels and the beginning of the industrial revolution, the sun's energy in its different forms, direct and indirect (such as wind and biomass) ?was the sole energy source that inspired and enabled the development of human societies.

Since then, and especially in the past one hundred years - a relatively short span of time - a powerful energy infrastructure that now covers practically the entire planet and is based on fossil fuels and nuclear energy has been built. Today the world consumes 9 billion toe per year, compared with around 500 million toe in 1860. While these energy uses and infrastructure do not yet benefit billions of poor people who still try to make do with firewood, they give humanity a power over nature that earlier generations never knew; they had to survive with the renewable energy of the sun.

This power helps us live more comfortably than past generations, but while it meets new needs, it also carries the risk of irreversibly altering natural balances, both local and global.

The world's population has been growing rapidly over the last century and continues to grow. We were 1.6 billion in 1900; we have now passed the 6 billion mark. If this trend continues, the human population will rise to about 9 billion by 2050. The increasingly crowded world has also become a world of cities. Fifty percent of the population already live in cities and the figure is expected to rise to 75% by the year 2050. Dozens of cities already number more than 10 million people.

Dramatic contrast between wealth and poverty has become part of any urban landscape, with excessive consumption among the richer segments and the inability of the poorer segments, especially in the developing countries, to meet their most basic needs: decent homes, clean water, health care, education. If these legitimate and ever-growing needs are to be met, energy consumption must increase. What part can solar energy play in this process?

Solar energy, past and future

With the exception of nuclear, geothermal and tidal energy, all forms of energy used on earth originate from the sun's energy.

Some are renewable, some are not. Renewable is the term used for forms of energy that can be regenerated, or renewed, in a relatively short amount of time. The regeneration process may be continuous and immediate, as in the case of direct solar radiation, or it may take some hours, months or years. This is the case of wind energy (generated by the uneven heating of air masses), hydro energy (related to the sun-powered cycle of water evaporation and rain), biomass energy (stored in plants through photosynthesis), and the energy contained in marine currents.

The energy contained in fossil fuels coal, oil and natural gas likewise comes from the sun's energy, but it was stored in plants millions of years ago, and once used, it cannot be regenerated on a human time scale. The earth's remaining fossil fuel reserves can probably provide us with energy for another 100 to 500 years, but this is an insignificant amount of time in terms of the whole past history of human civilisation and (one hopes) of its future.

The flow of renewable solar energies on earth is essentially equal to the flow of energy due to solar radiation. Every year, the sun irradiates the earth's land masses with the equivalent of 19 trillion toe. A fraction of this energy could satisfy the world's energy requirements, around 9 billion toe per year.