Solar cell basics

Converting solar energy to electricity via photovoltaic cells is one of the most exciting and practical scientific discoveries of the last several hundred years. The use of solar power is far less damaging to the environment than burning fossil fuels to generate power.

In comparison to other renewable energy resources such as hydro power, wind, and geothermal, solar has unmatched portability and thus flexibility. The sun shines everywhere.

These characteristics make solar power a key energy source as we move away from our fossil fuel dependency, and toward more sustainable and clean ways to meet our energy needs.

The sun is a powerful energy resource. Although very little of the billions of megawatts per second generated by the sun reaches our tiny Earth, there is more than enough to be unlimited in potential for terrestrial power production.

The sunlight that powers solar cells travels through space at 186,282 miles per hour to reach the earth 8.4 minutes after leaving the surface of the sun. About 1,368 W/M2 is released at the top of the earth’s atmosphere. Although the solar energy that reaches the Earth’s surface is reduced due to water vapor, ozone layer absorption and scattering by air molecules, there is still plenty of power for us to collect.

Harvesting photons for use in homes, factories, offices, vehicles and personal electronics has become practical, and economical, and will continue to increase in its importance in the energy supply equation.

In my opinion, the most exciting aspect of photovoltaic power generation is that it creates opportunities for the individual power consumer to be involved in the production of power. Even if it is only in a small way, you can have some control of where your energy comes from.

Almost anyone can set up a solar panel and use the power – independent of the grid and other "powers that be."

Batteries and super capacitors for the electronic devices that we use on a daily basis can be recharged by this natural and renewable energy resource. Doing so cuts down on pollution and makes life better for everyone. Practically every aspect of our lives will be touched in a positive way by the increasing use of solar electric power.

A solar cell is a solid state semiconductor device that produces DC (direct current) electricity when stimulated by photons. When the photons contact the atomic structure of the cell, they dislodge electrons from the atoms. This leaves a void which attracts other free available electrons. If a PN junction is fabricated in the cell, the dislodged photons flow towards the P side of the junction.

The result of this electron movement is a flow of electrical current which can be routed from the surface of the cell through electrical contacts to produce power. The conversion efficiency of a solar cell is measured as the ratio of input energy (radiant energy) to output energy (electrical energy).

The efficiency of solar cells has come a long way since Edmund Becqueral discovered the photovoltaic effect in 1839. Present research is proceeding at a fast clip to push the efficiencies up to 30% and beyond.

The efficiency of a solar cell largely depends on its spectral response. The wider the spectrum of light that the cell can respond to (the spectral response), the more power is generated. Research is ongoing to develop techniques and materials that can use more of the light spectrum and thus generate more power from each photovoltaic cell.

The reflectivity of the cell surface and the amount of light blocked by the surface electrodes on the front of the cell also affect the efficiency of solar cells.

Anti-reflective coatings on cells and the use of thin electrodes on the surface of cell faces help to reduce this loss of photonic stimulation. Another factor in cell efficiency is the operating temperature of the cell. The hotter a cell gets, the less current it produces.

Inherently, solar cells in use get hot, so it is important to have them mounted in such a way that they are cooled as much as possible to keep current production at its maximum.

Silicon is the most widely used material for solar cells today, though this is changing as thin film amorphous technologies are achieving greater efficiencies using materials such as gallium arsenide, cadmium telluride and copper indium diselenide.