There are two types of direct solar energy technology: solar thermal, also known as solar hot water and solar photovoltaic (PV).  Both of these technologies collect the suns rays that reach the atmosphere and convert them to energy.  While they both rely on the sun for energy how they do it differs dramatically.

Solar Photovoltaic Technology

Photovoltaic energy is based on the photovoltaic effect, by which a photon (elementary particle of light) impacts a panel composed of semiconductors.  Silicon is the main element in Semi-conductors.  When the photon impacts semi-conductors it releases electrons. This reaction generates electricity through exposure to light.  In photovoltaic energy solar panels, the semiconductors are shaped into thin layers that produce an electric current.  These semiconductors comprise the core element of solar cells  Semiconductors capture the electric current converting it into electricity for the house or business.

Solar Thermal Technology

Solar thermal operates on the principle that a fluid (water or other fluid) circulates in tubes in the solar panel while the sun’s rays heat it.  Flat plate panels or evacuated tubes hold water and circulate it through the water heating or home heating system with the use of pumps, These are “active systems”.  Water that circulates using the thermosyphon method is a method of passive heat exchange.  Thermosyphon is a natural method based on convection; as the water heats up it will push the cooler water. Residential solar thermal heating is usually combined with backup boilers to provide year-round heat and hot water.  Solar thermal energy is used to heat water and is also used for home heating by means of radiant floor, wall, ceiling, and roof piping in radiant panels.

Solar photovoltaic panels produce electricity, while solar thermal systems produce heat.  While both of these processes are energy efficient, solar photovoltaic only works during the day when the sun is out.  It can work on cloudy days, but the energy producing capacity will reduce to 10-30%.  Water heated by solar thermal will store for later use making it more energy efficient.  Most solar thermal systems have hot water storage tanks that will store the heated water until needed.

Savings Potential

Most people are only familiar with the PV solar systems for generating electricity for their homes. They have no idea of the tremendous savings potential of water heating by the sun. Solar thermal systems were the first use of solar energy and are energy efficient and cost-effective.  They are an effective energy efficient alternative to using fossil fuels to heat water and home or business  And like PV systems solar hot water systems are also eligible for the federal tax credit and most local rebates offered for energy efficiency.