太阳能（英语：Solar energy），是指来自太阳辐射出的光和热被不断发展的一系列技术所利用，如，太阳热能集热器，太阳能光伏发电，太阳热能发电，和人工光合作用。

自地球形成生物就主要以太阳提供的热和光生存，而自古人类也懂得以阳光晒干对象，并作为保存食物的方法，如制盐和晒咸鱼等。但在化石燃料减少下，才有意把太阳能进一步发展。

太阳能技术分为有源（主动式）及无源（被动式）两种。有源的例子有太阳能光伏及光热转换，使用电力或机械设备作太阳能收集，而这些设备是依靠外部能源运作的，因此称为有源。无源的例子有在建筑物引入太阳光作照明等，当中是利用建筑物的设计、选择所使用物料等达至利用太阳能的目的，由于当中的运作无需由外部提供能源，因此称为无源。

Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Irradiance may be measured in space or at the Earth's surface after atmospheric absorption and scattering. It is measured perpendicular to the incoming sunlight. Total solar irradiance (TSI), is a measure of the solar power over all wavelengths per unit area incident on the Earth's upper atmosphere. The solar constant is a conventional measure of mean TSI at a distance of one astronomical Unit (AU). Irradiance is a function of distance from the Sun, the solar cycle, and cross-cycle changes. Irradiance on Earth is also measured perpendicular to the incoming sunlight. Insolation is the power received on Earth per unit area on a horizontal surface. It depends on the height of the Sun above the horizon.