The trick is thermohaline circulation, basically salty water moves differently then fresh water in cold and warm environments. So to promote that effect the stage is tilted to allow warmer fresh water above cooler salty water below. Then a membrane moves the salt out of the circulation so as not to accumulate and clog the system.

The thing is that scaling this upward would present some challenges structurally to do large volumes OR the complexity would increase if they kept the same size and just made thousands of these little stages. Not to mention that, depending on what they're using for a membrane for salt removal, having a larger surface area could make it easier or more difficult to maintain. Easier in that you only need to clean it every so often (the membrane helps spread the load) or more difficult in that such a large membrane requires delicate processes to change out.

Also commercial production requires a fixed output, so with sunlight being variable any commercial installation would require storage.

But reading the brine discharge always makes me wish that grid based sodium ion batteries would be researched more. But can't have that because oil companies already put large deposits into lithium mines.