[basjoos]

I've never had mildew problems when drying clothes in my greenhouse dispite living in a very humid climate. I hang the clothes out in the morning and when the sun heats it up inside, the humidity drops very low.

I use a greenhouse to dry my clothes because I already have an existing greenhouse, but you don't need a greenhouse to do solar clothes drying. Something like a solar or Trombe wall with south-facing glazing, vents on the top and bottom to allow convective air flow, and enough height and depth to walk inside and hang your clothes is all that is needed.

You could even make it dual purpose with upper and lower vents opening to the living spaces of the house, as well as a separate set of vents opening to the outside. When using it as a clothes dryer, close the vents to the house and open the vents to the outside (unless you want to humidify the house in the winter). When using it as a house heater in the winter, open the vents to the house and close the vents to the outside.