In order to calculate the maximum number of solar panels that will fit on your roof, you need to come up with the square feet you have available.  To make this equation simple, lets assume that you have 1000 sq. feet of space that you would like to place solar panels often referred to as solar cells.

Next, you need to do some calculations to determine the size of the solar panels you will be using.  One of the most common solar panels is 15 sq. feet per panel.  They are roughly 5 ft by 3 ft.  So, for this example, we will use this size solar panel, which if you are wondering is usually about a 175 watt solar panel.

If the Dimensions of the roof are totally square, lets say 33ft by 33ft, which would equal 1000 sq. feet, we can figure this out.

First, take one side of the roof which is 33ft long.  And, lets subtract 3 feet from this side, because we need to have some roof for workers to walk on the roof.  So really, if we did this to all sides, the area we have to work with is now 26 ft by 26 feet.  That would mean that all edges of the original surface area are now taken in by 3 ft for safety.  Here is a diagram of a 33x33ft roof taken in 3 feet on each edge:

And, when the area is re-adjusted for the 26’x26′ usable solar panels space, it is going to look like the diagram below.  And if you want to maximize the space, you can end up fitting 40 panels on the roof like in the picture diagram below:

Please note that if you end up using solar panels for your roof which are lets say 200 watt panels, the dimensions could be considerably different, and would skew the diagram and ideas presented above dramatically, so of course it is best to consult with a solar company to get the exact numbers.