A temperature difference of 22°C between the cleaning water and the solar module surface carries a significant risk of thermal shock, which can cause micro-cracks and permanent damage to the panel's glass and cells.

 A temperature difference of 22°C between the cleaning water and the solar module surface carries a significant risk of thermal shock, which can cause micro-cracks and permanent damage to the panel's glass and cells.

Manufacturers and experts recommend the following guidelines to clean solar panels safely: 

Clean during low light conditions: The best time to clean is early morning or late evening, when the sun is low, the panels are cool, and the power generation is minimal.

Match water and module temperature: The water used for cleaning should be as close as possible to the module's temperature. Some manufacturers specify a maximum allowable difference of around 20°C between the water and module surface temperature to avoid thermal shock. A difference of 22°C exceeds or is at the very limit of safe operation.

Measure the temperature: Use a basic temperature gun to check the surface temperature of the panels before you begin cleaning.

Avoid using cold water on hot panels: The rapid change in temperature is what causes thermal stress. Panels can reach temperatures above 60°C (140°F) on a sunny day, even if the ambient temperature is lower.

Use appropriate water and tools:

Use deionized or low-mineral water to avoid mineral deposits (total hardness < 75 mg/L).

Use a soft cloth, sponge, or non-abrasive brush.

Avoid high-pressure washers (pressure should not exceed 35 bar or 500 psi). 

In summary, a 22°C temperature differential is likely unsafe. Wait until the panels have cooled down to a temperature much closer to the water temperature before proceeding.