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Shadecloth is a woven material that blocks most (not all) sunlight. It is rated by the amount of light blocked, so 90% shadecloth blocks 90% of the light (durrrr….). It can help keep direct sun off folks who need to park in full sun to make power.
If you look carefully you can also see full shade in the photographer's shadow, and on the edges of the shadecloth where the material is solid. Bonus: there is a dog in the shadows under the van.