All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Some scholars from the generation who followed the companions disliked performing ablution or Ghusl (ritual bath) with water directly heated by the sun from a medical perspective and not as a religious ruling. It is reported in one Prophetic narration that it causes leprosy, but this narration is not authentic. Ash-Shaafi'ee said: 'Water directly heated by the sun is not disliked except from a medical perspective.' Therefore, one should refer to specialized doctors in order to find out whether or not this matter is confirmed to be medically harmful, be that with solar heated equipments or directly from the sun or any other means.
Allaah Knows best.