Harvesting of this energy is free and non-polluting, but to build the components for energy harvesting requires materials, which have to be mined or obtained by industrial processes. Also the way we deal with old and broken parts (e.g. old solar panels) determines how clean this energy really is. Because if we just throw old solar panels on a pile in landfill, we will just recklessly let valuable materials rot and pollute our land and water. (Source where I got this information: https://greentumble.com/solar-energy-pros-and-cons/)