As renewable energy is becoming integrated into our everyday lives, new terms such as solar panel, photovoltaic and solar cell are more common and new devices, such as outdoor LED lighting are using this technology. The sun emits many forms of radiation. The best way to describe this is that there are ‘waves’ of energy that radiate from the sun at different frequencies.
This is only partially the truth as there is both a wave and particle nature to light.
The light spectrum is divided into different sections. It begins with the highest, gamma rays and ends with the lowest, long wave radio. Only a small portion of this is visible, called the visible spectrum and this occurs towards the middle of the range which lies between Ultraviolet and Infrared frequencies. Ultraviolet radiation is what burns the skin and can cause skin cancer. It is blocked by most types of glass and is partially reduced by the atmosphere especially the ozone layer. Infrared radiation is what provides the earth with heat and it is that which is trapped by green house gasses, carbon dioxide mainly and is causing global warming.
Infrared radiation is targeted by solar panels. This basically uses the energy generated by the radiation to heat water in pipes that flows and generates electricity. This can be used to charge a battery which could then power said LED lighting. As mentioned previously there is a dual nature to light. It consists of both a particle and a wave. It might help to think of the particles moving in a wave like pattern but the reality is more complex than that. The important thing to remember is that the light particle, the photon, is what is targeted by a solar cell.
Generally speaking the solar cell works by providing energy to a semiconducting material, most commonly silicon, so that electrons within the material are released from the bonds to their atoms in the semiconductor.
The arrangement of the cell into strips of conductor and semiconductor allow these freed electrons to move. They move in a directed manner away from the incoming energy, the photons, creating a flow of electrons more commonly known as current.
A high incoming rate of photons is required to release the electrons. This creates problems as much of the higher energy (higher frequency) waves emitted by the sun are blocked; the glass protective covering reflects light requiring anti-reflection membranes, glass blocks ultraviolet and the lower range of frequencies like infrared do not have enough energy to have much of an effect on the panels. Thus these panels only really target the visible spectrum which is only a small proportion of the sun’s energy.
Yet, with the improvements to the semiconductors, the anti reflection layers and the methods of directing the released electrons the efficiency of solar cells has dramatically improved. Huge fields of cells are being created in deserts and mountainous regions that can now produce kilowatts of energy.
Combined with the improvements of energy efficient products, such as LED lighting, this is becoming a valuable resource. In fact, the low energy of LED lighting is one of the most important improvements as it helps to alleviate the greatest weakness of solar cells – night time.