Utility Scale PV Systems

APS Flagstaff PV sAPS

APS recently issued two separate Requests for Proposals for solar and wind resources that will help expand their renewable energy portfolio to approximately 2,500 megawatts by 2021. The first RFP is seeking competitive proposals for up to 150 megawatts of APS-owned solar resources to be in service by Dec. 31, 2021. Projects must employ commercially proven technology and must be designed with the flexibility to add energy storage as a future option.
The second RFP is for up to 250 megawatts of wind resources to be in service as soon as possible, but no later than 2022.
According to the APS posting on www.arizonagoessolar.ord in November 2019 APS has 26 MWac APS owned and 840 MWac utility scale systems connected under power purchase agreements (PPA)owned by others.



SRP large batterySRP

As part of its commitment to reduce carbon emissions and invest in 1,000 megawatts of new utility-scale solar energy by 2025, Salt River Project has invested in two new solar energy + battery storage plants.

The Sonoran Energy Center will be the largest solar-charged battery project in the state and the addition of these two plants will make SRP one of the largest investors in energy storage in the nation.

Combined, these plants will generate enough solar energy to power approximately 100,000 homes and will store excess energy in state-of-the-art battery storage systems that will be available to customers during the peak energy usage period when demand is at its highest.

The solar plants will also contribute to the SRP goal of adding 1,000 megawatts of new utility-scale, solar energy to its system by the end of fiscal year 2025 as well as SRP’s 2035 goal to reduce the amount of carbon emissions per megawatt-hour by more than 60 percent and by 90 percent in 2050.

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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))))


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