There's only so much sunlight that reaches any point on the Earth throughout the day. You could build something really tall to collect more light from the sun a

There's only so much sunlight that reaches any point on the Earth throughout the day. You could build something really tall to collect more light from the sun at more angles, but that will cast a shadow and reduce what's available for other collectors. So you end up with a lot of collectors receiving little sunlight or fewer collectors spread far apart.