From Space to Earth: The Story of Solar Electricity

  • John Perlin
Aatec: 1999. 224 pp. $32, £22.50

Ever since the French scientist Henri Becquerel discovered the photoelectric effect in 1839, researchers and engineers have been infatuated with the idea of converting light into electric power. There is a magical aspect to solar cells that attracts a wide spectrum of people ranging from illiterate amateurs to highly trained professionals, from penniless entrepreneurs to wealthy sponsors. Their common dream is to collect the energy that is freely available from sunlight and turn it into the valuable and strategically important asset that is electric power.

Light work: solar cells are becoming efficient enough to rival conventional solid-state cells. Credit: PHILLIPE PLAILLY/SPL

The development of solar cells is also promoted by the increasing public awareness that the Earth's oil reserves will run out this century. As the planet's energy needs will at least double within the next 50 years, the stage is set for a major energy shortage unless renewable energy can cover the large deficit that fossil fuels can no longer furnish. Public concern has heightened recently as a result of the disastrous environmental pollution from oil spills and the frightening climatic consequences of global warming from the combustion of fossil fuels.

Fortunately, the supply of energy from the Sun to the Earth is gigantic — 3×1024 joules per year, or about 10,000 times more than mankind's current consumption. In other words, covering only 0.1 per cent of the Earth's surface with solar cells possessing an efficiency of 10 per cent would satisfy our present needs.

To tap into the Sun's huge energy reservoir remains, nevertheless, a major challenge for mankind. John Perlin's book gives a taste of the tremendous difficulties that early pioneers had to overcome in order to turn Charles Fritt's 1885 invention of a selenium-based solar module into today's booming photovoltaic business. Solar cells functioned very poorly for long after their discovery, with conversion yields of below one per cent. They remained a curiosity until 1954, when Calvin Fuller and Gerald Pearson from Bell Laboratories realized the first silicon-based p–n junction device, which achieved an efficiency of close to six per cent.

Despite such an impressive advance, this would probably not have been exploited commercially without the advent of the space age. It was the need to power satellites that gave the breakthrough to solar cells. Only space applications were able to afford their very high price, that is, several hundred dollars per watt of electric power produced by the solar panels. When the price of solar cells dropped to $20 per watt they became competitive with primary batteries for remote-site terrestrial applications, mainly in the telecommunications field. Today the cost has come down to $5 per watt, opening up commercial opportunities for building integrated solar installations connected to the grid.

Starting with the space application, Perlin gives a vivid and fascinating historical account of the advances of photovoltaics on Earth. His book tells us the success story of the pioneers of solar cells, crediting them for their imagination and perseverance. One of the remarkable individuals described is Father Bernard Verspieren, who saved many lives by installing solar-driven water pumps in Mali. Presenting the history of the development of photovoltaic cells in such a personalized manner makes it a much more lively and interesting read than a mere technical account would have done.

The book focuses strongly on silicon; gallium arsenide cells, currently the most efficient solar-light-energy converters and widely used in space applications, are not mentioned. Nor are thin-film molecular photovoltaic systems such as the nanocrystalline-injection solar cell, which has an efficiency of more than 10 per cent, becoming a credible rival to conventional solid-state cells.

I would have liked a more extensive assessment of the future potential of photovoltaics, going beyond its use as a power source for the telecommunications industry. The crucial question is whether solar cells can supply energy for the planet on a major scale. The world currently needs 10,000 gigawatts of power, a staggering figure compared with the present yearly installations of 100 megawatts' worth of photovoltaic panels.

Novel concepts that do not rely on conventional p–n junctions may well be necessary to achieve the significant cost reduction required for large-scale applications of solar cells. The newly emerging field of molecular photovoltaics holds great promise in this respect. These systems operate like a plant's photosynthesis, mimicking a process that has worked well for the past 3.5 billion years, providing all the world's fossil energy reserves. The use of artificial photosynthesis for converting and storing solar energy provides exciting prospects for the new millennium.