A solar panel is a device that collects and converts solar energy into electricity or heat which can be used by (for example) nearby buildings. Solar photovoltaic panels can be made so that the sun's energy excites the atoms in a silicon layer between two protector panels. Electrons from these excited atoms form an electric current, which can be used by external devices. Solar panels were in use over one hundred years ago for hot water heating in homes. Solar panels can also be made with a specially shaped mirror that concentrates light onto a tube of oil. The oil then heats up, and travels through a vat of water, instantly boiling it. The steam created turns a turbine for power