Why does coal power leave far more toxic waste per unit of electricity than solar panels do?

Answer: Burning coal leaves a steady stream of ash that concentrates toxic metals

Burning coal leaves a steady stream of ash that concentrates toxic metals ✓ — Burning coal leaves ash, tens of kilograms of it for every megawatt-hour, and that ash concentrates the arsenic, mercury and uranium that were spread thinly through the coal. A solar panel's hazardous content is made once and then spread over 25 to 30 years of output, so per unit of electricity coal leaves roughly 50 times as much waste as solar.

Solar panels contain no hazardous materials, so only coal makes toxic waste — Solar panels do contain small amounts of hazardous material, such as lead in solder and cadmium in some thin-film types, so coal does not come out worse by default. The gap comes from scale: a panel's few kilograms of waste are set against a coal plant's continuous stream of toxic ash.

Solar panels are fully recycled at the end of their life, so they leave no waste — Most end-of-life panels are not fully recycled today: the glass and aluminium frame are easy to recover, but separating the rest is costly, so panel waste is real. It is still tiny beside coal ash, which is why coal leads by such a wide margin per unit of electricity.