[kragen]

photosynthesis is about 3% efficient

the most popular solar panels are about 21% efficient

solar panels don't require maintenance, though efficiency drops if they get dusty

trees commonly require a lot of maintenance, i guess you don't know any gardeners; most afforestation and reforestation projects totally fail because they neglect this

but the biggest issue is that trees generally don't desalinate seawater

mangroves sort of do, but their output is water vapor, and generally growing mangroves in ocean water decreases evaporation from that ocean water rather than increasing it

in summary, how pv-powered desalination compares to just planting trees is that pv-powered desalination produces fresh water and planting trees doesn't