Very little, apart from keeping your solar panels clean.

ET Solar recommends the following maintenance items to ensure optimum performance of the module: Clean the glass surface of the module as necessary. Use water and a soft sponge or cloth for cleaning.

Solar modules may become soiled to varying degrees depending upon surrounding conditions and this may reduce their performance. Periodic cleaning of the modules will ensure maximum output. However, if modules are installed at height (e.g. on a roof) then cleaning should only be performed by qualified personnel.

Over time, dirt and dust can accumulate on the glass surface of the module, reducing its power output. Yingli Solar recommends periodic cleaning of PV modules to ensure maximum power output, especially in regions with low precipitation.

Suntech recommends the following maintenance in order to ensure optimum performance of the module: Clean the glass surface of the module as necessary. Always use water and a soft sponge or cloth for cleaning. A mild, non-abrasive cleaning agent can be used to remove stubborn dirt.

"It is important to know and understand the warranty requirements of the specific products used in a PV system.  Not all warranties are created equal.  Warranty requirements not followed, including documenting regular conducted preventative maintenance, can result in a voided warranty.  Typical warranty requirements are strict regarding tasks that must be performed.  However, the tasks are simple and serve to protect the products and ensure greater long-term reliability."

To optimize electrical output it is recommended to clean the panels when dirt can be seen on the glass surface.  If dirt remains on the panel, it may cause cell shading which will reduce power output or even cause further damage.  To clean either the front or rear of the panels, use only de-ionized water at ambient temperature.