Your panels are subject to be covered by pollen, dust, ash and other debris floating in the air. Not only does this look bad but these elements sit on top of the solar panel surface blocking the panels from absorbing the solar rays of the sun. This blockage reduces the production of energy for your home or building. Even the smallest amounts of dust can noticeably decrease the energy output. Something else to consider is that your warranty may require these panels to be routinely cleaned.