Location, location, location!
Kotrenin the problem with your argument is that you assume this is going to be built in the middle of a flat spot.
You could easily build these going up the side of a mountain, get advantage of stacking effect. Get the advantage of their being more acres on a slope. And not worry about blocking anything. Or it could be built on the north side of an Island where it shades only water.
If you build it up the side of a mountain you could probably build catch basins to catch snow/rain, filter it and setup a gravity flow system with no need for pumps.
Near the ocean you might need to use a seawater algae, in which case you just need enough solar cells to power the pumps, not a deal breaker.
There is a LOT of waste land out there that is not suitable for farming, or development.
Those are prime locations for alternative energy production, be it Wind, Solar, or Algae driven.