Doesn't grass need photosynthesis?

Grass doesn't need direct sunlight to grow. Since the sun moves, only a very small percentage of the area is in shadow all day anyways.

I am passing by a solar farm as I am writing this. And The grass below and beside the panels looks the same.

Here is a pic I found on the internet:

https://cals.ncsu.edu/wp-content/uploads/2016/09/Sheep-Solar...

But there is no such thing as a free lunch, although the grass will transpire less water in a solar farm, it also doesn't grow as fast.

There's a lot of things that go into plant yield, and it's not just as simple as "less sunlight, less grass".

Most plants can use only a few hours of direct sunlight before they run out of stuff to photosynthesize out of. They endure the rest of the day trying not to get dehydrated, and spend the night stockpiling raw materials to process next day.

Cereal crops are bred to be able to use more sun than most plants; most chase other goals than the big seeds we select for.

Maybe. Maybe!

But you get a ton of electricity

There is sufficient indirect light underneath ground mount solar that many plants can grow happily. Lots of plants prefer shade over direct sun.

This is also why bifacial solar panels are so much more efficient.