Ex Conservatory DG panel - Solar hot water panel

I have made some solar hot water panels but am having problems with mist forming on the glass when the inside becomes hot. I am seeing a mostly dry deposit (a little greasy in areas) causing a misting. This only occurs when the temperature inside is >100 Deg C (max I have measured is 130 Deg C).

I was wondering if the problem may be agrevated by coatings on the glass, does anyone have any thoughts?

Would it be possible to remove any coatings by polishing with jewlers rouge (if it would help)?

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