What is Solar panel?
[[File:Symbol for Solar Panel.jpg|thumb|Schematic symbol for Solar Panel]] '''Solar panels''' get [[energy]] from the [[sun]] for people to use. There are two types of solar panels, those that collect heat (thermal), and those that produce electricity ([[photovoltaic]]). Heat from solar panels is often used for space heating and for hot water. Solar panels collect [[renewable energy]]. In the 20th century, some used the [[heat]] of the sun to make steam for a [[steam engine]] to turn a [[generator]]. Nowadays producing [[electricity]] from the sun's [[light]] is cheaper. This is a [[solid state]] way of producing electricity, meaning that it has no moving parts. Home solar panels are often mounted on rooftops. Commercial or industrial installations are often on trackers mounted on the ground. The trackers point the panel towards the sun as the sun moves across the sky. Photovoltaic panels are also commonly used in [[outer space]], where they are one of the few power sources available. == Heat == Solar panels for heat are usually made from a box with a clear window on top. Pipes run through the box. The pipes and the box are usually painted black because black absorbs more heat than other colors. The pipes are filled with a [[heat transfer]] fluid such as water or oil. A pump circulates the fluid, which heats up as it is exposed to the sun. When the hot fluid leaves the panel, it goes into a [[heat exchanger]], which transfers the heat into water or air. After the now cool fluid leaves the heat exchanger, it is pumped back up into the panel to collect heat again. == Recycling == Photovoltaic solar panels are built to last about thirty years. So far, most of the solar panels, originally created in the 1980's have not yet reached the end of their estimated lifespans. Many of the solar panels which have expired, however, have been classified as [[hazardous waste]]. The used solar panels that have not been considered dangerous can be recycled to create new solar panels.<ref>{{Cite web|title=Solar Panel Recy