Bird droppings, dust, and pollution can all reduce solar panel efficiency. Solar panels that are cleaned twice a year produce a much higher % of electricity respectively than those that are left uncleaned.

You will see a big boost in your system performance, and big cash savings on your electric bills.
Neglecting to clean your solar panels is like throwing money out of the window.
Solar panel cleaning services are available for those in the South Orange County area (see our service areas) at the bottom of the page.

We know that dust, dirt, pollen, bird droppings, and other debris can negatively affect solar panel efficiency. ... They found that cleaning the solar panels was “the number one way to maximize the energy they produce.” Cleaning solar panels that had been in operation for 15 months doubled their output of electricity.

This literally means that they will generate up to 25% less electricity, which you now will have to source from the utility company at their price rates. This easily adds a lot extra to the payback time.