Sun storage maximum of 9999
If you are using tile turnip you can’t add anymore because the cost of the tile turnip after 8 or so is more than what your sun storage max is even if you have earned tons more sun than 10,000
Forum Discussion
I think this was done on purpose. It was designed to restrict the amount of tiles could be placed with the original level 1 plants, 7 is the maximum allowed. However, with the introduction of plant leveling, more tiles were allowed but the maximum number is depending on how high of a level that the Tile Turnip has been upgraded.
At level 10, the cost stays at 200 suns and you can cover the whole lawn (with 45x tiles) if you so wish.