The solar panel consists of solar cells covered with a protective glass. The outdoor location of the solar panels allows for dirt build up on the panels, causing a decrease in electricity production and reduced profits. In some systems, dirt accumulation on one panel will reduce the output of the group of panels connected to the same inverter. As more dirt accumulates on the panels, the power output is compromised. Other factors may affect the power output, but the presence of dirt is the most significant of them. Experts agree that the decline in output power can reach 25%. According to data from the National Renewable Energy Laboratory in the U.S., completely avoiding cleaning the panels will reduce output and profits by 30%.