How does solar energy cause pollution?
Not very much. There is some pollution associated with the manufacturing of solar panels and there is an ecological footprint related to the land needed.
Once a solar panel is installed, it has no pollution associated with it - it just sits there and produces electricity. The manufacturing of panels does take energy and if the plant is in a fossil fuel powered country, there will then be some CO2 associated with this process. Sometimes there are other chemicals used in the production of panels, which can leak into water systems if companies are not careful.
Small solar on existing rooftops does not have a land footprint but some very large solar thermal plants can takes up large tracts of land and by so doing, possibly impact local ecosystems. However, many such plants are often ideally located in hot dry desert environments that is not known for a huge biodiversity to start with.