This can be a major problem. As I used to be a Salt Water Chlorinator Technician, this was the first thing we learned about. 

There are two things to do when fitting a solar system to a pool with salt water chlorination.
1/ plumb the solar feed and return before the salt cell (the customer will have to turn up the output of the chlorinator to counteract the effects of warm water flowing across the cell reducing the effectiveness of the chlorine manufactured)
2/ Make sure the salt cell has a gas trap. i.e that the pipework goes up above the filter to the cell the back down. That way if the flow switch/sensor fails, the hydrogen will get caught in the gas trap and stay there and not affect anything.

If you would like more information, please feel free to contact me