Joe, of Balclutha Primary School, asks :-

How do solar panels work?

Bob Lloyd, a physicist at the University of Otago, responded.

There are two main types of solar panels. One type is the solar thermal panel of the variety used to generate hot water for households. These work by absorbing the solar energy from the sun directly as thermal energy or heat and using this energy to raise the temperature of water, which can be stored in a tank for later use.

The other type of panel is the photovoltaic (or PV) panel and this type can be used generate electricity directly from solar energy. The photovoltaic effect was discovered way back in 1839 by the French scientist Becquerel but not really commercialized until the 1950s by the Bell Telephone Laboratory for the US space program. PV cells work by using the energy in sunlight to directly alter the energy levels in certain individual atoms to cause an electric current to flow. The action is a little like photosynthesis where sunlight causes direct chemical changes in chlorophylls (in plants) to change carbon dioxide in the atmosphere directly into carbon.

In the case of the solar cell the active ingredient is often very pure silicon made into a semiconductor diode. When sunlight hits the solar cell an electron is given sufficient energy to allow it to become a conduction electron, producing a voltage across the cell of around 0.6 volts. By placing a number of the cells in series, a solar PV panel can be made to deliver 12 volts or more. The efficiency of the conversion of sunlight to electricity is currently around 15 per cent meaning that around 7 square meters of panel area is needed to produce 1000W of maximum electrical power i.e. when the panel is facing the sun and there are no clouds overhead.