I don't think they are talking about the impact on the environment. I think they are talking about the procedures for operating the equipment.
The way I read it, they mean whoever operates this device does not have to periodically go empty some bin/tank of salt or brine.
An analogy would be to a frost-free refrigerator. When you say the freezer compartment of your fridge is frost-free, you don't mean that it never generates frost. You mean it does generate frost, but it also automatically removes it. It's "free" of frost in the sense that you are free of doing a chore that you have to do with a freezer that lacks this feature.
If you operate it directly on the open ocean, towing it behind your sailboat, you don't have to do anything special.
If you operate it in a commercial, protected context where you pump water through it, you will generate brine.
If you operate it en-masse in the ocean, the things that are insignificant at the scale of 1 and 10 square meters may become significant at the scale of 1 and 10 square kilometers.
All of these things are true for other desalinization systems, too. Claiming "you don't have to worry about brine" because it floats on the water surface is misleading at best. You can put any system you want on the water and make it float -- we have concrete and steel hulls, no problem -- but that doesn't solve the concentration problem.
It sounds like they're targeting small deployments in the developing world, at the scale of 1 to 10 square meters, not large commercial systems.
From the article:
> In production, they think a system built to serve the needs of a family might be built for around $100... The hope is that it could ultimately play a role in alleviating water scarcity in parts of the developing world where reliable electricity is scarce but seawater and sunlight are abundant.
The problem with brine from desalination plants is that it's released at high concentration in one spot. This would not suffer from that problem.
The way I read it, they mean whoever operates this device does not have to periodically go empty some bin/tank of salt or brine.
An analogy would be to a frost-free refrigerator. When you say the freezer compartment of your fridge is frost-free, you don't mean that it never generates frost. You mean it does generate frost, but it also automatically removes it. It's "free" of frost in the sense that you are free of doing a chore that you have to do with a freezer that lacks this feature.