Condensation is caused when warm air collides with cold surfaces. So if the sheets are cold and the air inside is warm (i.e. you have it installed in a sun-room or similar) you will get condensation on the inside. Even if the sides are open, but the sun heats the air underneath the polycarbonate, more than the air above it, you will still get condensation.
The only way to stop this is to ensure that the temperature under the sheets is the same as the temperature outside, by using adequate ventilation.
Because Twinwall is insulated (like double glazing), it reduces the chances of getting condensation. So it’s more suitable for enclosed areas.