flat array                      tilted array

One of the most unfortunate mistakes made in PV system design is the flat mounted array.  You should ALWAYS mount modules in a tilted configuration. Lets explore the benefits of the tilted array…

1) More power production results from better sun angle - Modules tilted up toward the southern horizon in the northern hemisphere (or towards the north in the southern hemisphere) will produce considerably more power than modules that are flat.

2) Sheeting of rain water promotes module cleaning - Tilting your array promotes sheeting of rain to clean the modules.  Flat modules are a wonderful catch basin and turn into a a shallow puddle every time it rains.  An even bigger problem can result  if that shallow puddle or water freezes because the expansion of the water can literally tear the module apart causing premature failure that is not covered by module manufacturer warranty.  Even PV arrays near the equator are tilted 5-15 percent to allow the water to drain and clean the module.  This technique results in more power production.  Flat arrays allow the dirt to bake in and this can cause a reduction in power output of 30% or more when they get very dirty over time.

3) Improved airflow cooling allows more energy output – Flat arrrays do not allow convective airflow cooling.  Modules that are tilted allow cool air to be sucked in from the bottom of the array and exit the top of the array cooling the modules.  Cool modules produce more electricity than hotter modules.  Arrays that are hotter will not produce as much power as arrays that are air cooled.  Another benefit of better airflow is longer life.  Modules in a flat array experience more thermal cycling and this breaks down the laminated backsheet causing shorter module life.

I sometimes hear the arguement that you can fit more modules in a flat array (with no walkway between the modules) compared to a tilted array with space between the rows.  While you can fit more modules and DC watt rating in the same space, all that extra DC watt rating is squandered by poor sun angle, baked-on dirt shading, and higher temperature operation.  Higher temps sap electrical output and and cause premature module failure.  Also having walkways between the rows is imperative to safe and effective array maintenance.  Having no walkway between modules increases the possibility that somebody will walk on the modules and cause premature unwarranted failure.

You will get more power, better life, and better bang for the buck with a tilted array.  Dont make the mistake of mounting modules flat.  Your customers will thank you.