Early morning or late afternoon is usually the best time to clean solar panels when they're cool and not directly exposed to sunlight, which can cause water to evaporate quickly and leave streaks.

Soap or detergent diluted in water can be used to clean solar panels effectively. Avoid using abrasive cleaners or harsh chemicals that can damage the panels' surface or coating.

It's not recommended to use a pressure washer to clean solar panels as the high pressure can damage the panels' surface or coating. Stick to gentle cleaning methods to avoid any potential damage.