Solar and wind energy are two primary sources of renewable energy utilized today in green building practices to promote a greener environment.  Solar energy is derived from sunlight, while sources of wind energy are developed as airflow runs wind turbines.  These sources of renewable energy produce no greenhouse gases during operation, such as carbon dioxide or methane.  Solar energy can be classified in two categories:  heat (thermal) energy and light energy.  Solar thermal technologies (solar thermal collectors) use the sun’s heat energy to heat water and air for uses such as space heating, water heating and pool heating.  Solar light energy uses photovoltaics (PV) technology, which is a semiconductor-based technology that converts light energy directly into an electric current.  Photovoltaics are sold as panels and are also being integrated into building materials, such as PV roofing shingles.  In wind energy technology, a wind turbine collects kinetic energy from the wind and converts it to electricity that is compatible with a building or home's electrical system.  A wind turbine can lower electricity bills by as much as 50 – 90% and produces no pollution.  Providers in this category provide environmentally friendly products and services related to solar and wind energy technologies and systems, such as solar thermal collectors, photovoltaics, solar panels, wind turbines and more.