Solar energy introduction 

And then there was light

Suns - our Sun

There are uncountable suns in the universe - at least 70 trillion visible ones by the last count and an unknown number beyond our visibility - and as such they are a common occurrence in the universe.

The use of the sun as an energy source is not new. Nature has been utilizing this for many millions of years. Sunlight is necessary for our biosphere to function in its current configuration, including our own bodies. Photosynthesis, the process of utilizing light as energy, is integral to plant life, which in turn is integral to the biosphere as a whole.

Our human civilization, from its earliest to its classical roots to our modern society, has had an equal fascination of the sun. Seeing it as (a) god, and the provider of life, for example. Many past rulers even  claimed to be direct descendants of the Sun such as the Incas in South America and the Egyptians in Northern Africa.

In our current scientific age we have grown beyond such simple beliefs but it is easy to imagine that an object which burns brightly in the sky for half the time and which brings darkness when it is not seen, is viewed in awe and accredited divine power and that rulers have used it to enforce their own hold on the masses. 

Today, we know the sun for what it is, a part of the living and evolving universe. Part of the star family and an energy powerhouse with a life cycle of its own.

Energy output of the sun

The sun's energy output is quite stable. Called the radioactive output or solar constant its radiance gives off 137 ergs per square meter per second (ergs/m²/sec).

This is equivalent to 1.98 calories per square centimeter per minute (cal/cm²/min).

This energy is beamed at the Earth and seldom varies by more than 0.1 percent.

An 11-year sunspot cycle, magnetic activity emanating from transient strong magnetic field regions provide a fascinating feature of this energy output.
 

Harnessing the power of the sun

As our planet gets more polluted by the use of fossil fuels, many companies, organizations and government institutions worldwide are looking for alternative, affordable and sustainable sources of energy.  

So far, out of many alternatives, like nuclear, fusion, wave, wind, friction and other possibilities, solar and wind energy seem to be the better choices in that they are clean, widely available and more cost effective in the long term. 

However, for the amounts of energy required by our civilization to work and progress, solar energy is thus far not efficient enough to be used on a very large scale as a main energy source.

On the other hand, if many of our smaller devices at home or on the road can be run off solar energy it would reduce the demand for more traditional energy sources. For example, a solar energy kit costing a few hundred dollars can easily run your pc, all its peripherals and a couple of lamps besides. And so there are many appliances in our daily lives that can be run on solar cells.

Solar energy is already used in many places around the world to power independent devices, such as road side emergency telephones (France), road lighting, measurement equipment and such (see Solar Energy News and Development).

The discovery and development of solar cells

Solar cell history

Solar cell development originated with the research and work of the French physicist Antoine-César Becquerel in 1839.

While experimenting with solid electrodes in electrolyte solutions he noticed what is now known as the photovoltaic effect, that voltage occurred when light fell on the electrode.

Some 50 years later Charles Fritts built the first real solar cells. By coating the semiconductor selenium junctions with an ultra thin layer of gold he was able to achieve a 1% conversion of light into electrical energy. Not very efficient by today's standard but he proved the viability of using light as an energy source.

It was enough, however, to earn praise from contemporaries, and visions of clean energy and clean air, not to mention unlimited energy, abounded.

Efficiency of conversion being the main bottleneck for early solar cells, other materials were experimented with. By the 1930's selenium and copper oxide cells had been developed and were used in photometers (light measurement) for photographic purposes. Efficiency, however, remained at less than 1%.

In 1941 the first silicon solar cell was developed by Russell Ohl. In the 1950's American researchers achieved a 6% efficiency using direct sunlight and by the late 1980's silicon solar cells, as well as solar cells made of gallium arsenide achieved efficiencies of more than 20%.

Concentrator solar cells, where light intensity is increased by using lenses, achieved efficiencies as high as 37%.

Solar cell basics

Solar cells are designed to convert light into electrical energy. They are generally arranged in lines, grids and arrays, depending on the energy need, up to thousands of cells and millions of cells.

The greatest aspect of solar cells is that they require neither fuel for combustion nor moving parts that need to be serviced. This makes them ideally suited for remote areas and long term use, including space.

Communications and weather satellites, road lighting, calculators, portable radios, navigational aids such as buoys, are all ideal applications for being powered by solar cells to provide the necessary electricity.

Many of the smaller solar energy appliances do not even need sunlight. Artificial light such as in offices or homes works perfectly well to power them.