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PV Row to Row Spacing

 

If your system consists of two or more rows of PV panels, you must make sure that each row of panels does not shade the row behind it. To determine the correct row-to-row spacing, refer to the figure above.

There is no single correct answer since the solar elevation starts at zero in the morning and ends at zero in the evening. The sunshine (irradiation) on an array has three components, direct beam, diffuse (blue sky and overcast), and reflected from the ground in front of the array. Here we will consider only the direct beam that is subject to shadowing by the row in front (or even a wall).

The elevation of the sun at noon on December 21st in the Northern Hemisphere is basically 90-23.45-latitude (in degrees). In most cases 90% of the unobstructed irradiation on the array occurs when the solar elevation is above 50% of the maximum winter elevation. The elevation correction is therefore 50%. This may be excessive for rows that are less than about 4 times the height of the panel.

To solve for X (the minimum distance between the rows), use the equation below:

X = L (cos(tilt)+ (sin (tilt) * tan (lat + 23.5+(50% of elevation))))

Where

L = panel length
tilt= panel tilt angle
lat= geographic latitude of your system.


Calculated values are:

Winter minimum noon solar elevation = 90-23.45-latitude
90% of unobstructed elevation = 50% of Winter minimum solar elevation

The Excel spreadsheet version of this is:

Spacing Excel

The Excel formula can be copied >>> =B1*(COS(B2*PI()/180)+(SIN(B2*PI()/180)*TAN((B3+23.5+B5)*PI()/180)))

Effect of PV Array Orientation - Phoenix AZ

The following chart shows the calculated PV system output for a system in the Phoenix, Arizona area for a variety of array orientations. The calculations assume an open array in free air such as a pole mount or parking canopy without anything under the modules. Mounting PV modules on a roof reduces the output due to the higher temperatures. PV modules mounted flush with a roof, but with at least 3” of space below the modules and mounting structures that allow some air flow, will have an annual energy reduction of about 6%. Of course, these calculationa assume no shadows on the PV array.  The calculations include normal inverter efficiency, wire loss, and an allowance for dirt.
 
In the chart the upper line shows the roof pitch (4/12 represents 4" of slope per 12" of roof), the angle the pitch represents, and the direction the PV module face (NW=North-West, etc.).The larger number is the annual output in kilo-Watt-hours (kWhr) per year for a PV array with a nominal rating of 1000 Watts.  For instance, if the PV array has 20 PV modules with a rating of 310 watts (STC) per module, the array is rated 6.2 kilo-Watts DC (kWdc). To estimate the annual output using this chart, simply select the closest orientation, such as South facing at 3/12 pitch, and multiply the 1668 by 6.2 to get the annual output of 103,416 kWhr.
kWhr vs orientation Phx

After APS explosion injures 4 firefighters, Arizona cities enact battery storage laws for utilities, homeowners

There is an interesting, but non-technical, article in the Arizona Republic about batteries in PV systems.

Most of the major Phoenix area cities have documents that detail the requirements for new solar systems and it is likely that the cities will be updating their documents soon with battery requirements.

After APS explosion injures 4 firefighters, Arizona cities enact battery storage laws for utilities, homeowners