Keeping the module perpendicular to the incoming sunlight means that the module intercepts the maximum amount of sunlight. If you have trouble visualizing this concept, take a paper and hold it up to the sun while observing its shadow. If the paper (or module) is edge on to the sunlight, then it casts a small shadow. If the paper cover (or module’s face) is perpendicular to the sunlight, then the shadow is as big as it will ever be. The size of the shadow shows us exactly how much sunlight is being intercepted. In the case of a PV module, maximum shadow means maximum power.

The problem is that the Sun constantly moves in relation to the stationary PV module. Actually, the apparent motion of the Sun is due to the Earth’s motion Even if we place a module so that is perpendicular to the Sun at solar noon, it is not even close to perpendicular in the morning and evening. This daily east to west solar motion is called solar azimuth. Also consider that the Sun’s apparent height in the sky changes from winter to summer. This yearly north to south solar motion is called solar declination.

Mant researches calculate the best tilt to optimize energy output from one panel. but what about the other panels in the array? Here I will try to show how shadow add difficulty in designing solar field.

We all know that a solar panel is a sequence of cell connecting in a series. Kyocera present it in its module characteristics the shade issue very well - partial shading, even one cell of a 36 cells module , will reduce it power output dramatically.



That is why shade is something to take into considerations while designing an panel array.
In order to understand the problem I build a model that analyzing the shadow profile of every hour during the year (Lat-31', Long.-34') and this is the result for January and February.





This is the exact amount of hours the area behind a module suffers from shadow (the diagram above presented a 3X6 meter behind the panel, green area represent no shadow, yellow few hours of shadow, and red is more then 40 hours of shadow in 2 months only).
It is very clear that an area of 3-5sqM from the panel suffers from shadow. If we add the aspect of the panel (i.e. if shadow shade only 10% of the adjacent panels then the impact is close to 100% reduction) it makes the area even larger.

As refers to trackers, a research I read about trackers show that this problem is 3-5 times more with trackers then without them. That is why trackers are not so much in use in places where land is limited.

The study I made based on geometric calculations of combined movement of the sun azimuth during the day and the altitude of the sun along the year.

For a  full year diagram please contact me at yanir@bizbee.co.uk