The working principle of solar panels is to use photoelectric effect, also called photovoltaic effect. Photovoltaic effect refers to the phenomenon that an object generates electromotive force due to absorbing photons. When the object is exposed to light, an effect of electromotive force and current caused by the change of charge distribution state in the object. When sunlight or other light irradiates PN junction of semiconductor, photovoltaic effect will be generated. Photovoltaic effect causes voltage on both sides of PN junction, which is called photovoltaic voltage. If the PN junction is short-circuited, current will be generated.